Add second year
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- #[[CT255 - Next Generation Technologies II]]
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- **Previous Topic:** [[GDPR]]
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- **Next Topic:** null
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- **Relevant Slides:** 
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id:: 63265db7-1d41-44f7-b4cf-0bab377a7c1c
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-
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- ## SQL Injections
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- What is an **SQL Injection**? #card
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card-last-interval:: 4
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card-repeats:: 1
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||||
card-ease-factor:: 2.36
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||||
card-next-schedule:: 2022-09-22T14:46:36.580Z
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||||
card-last-reviewed:: 2022-09-18T14:46:36.581Z
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card-last-score:: 3
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- An **SQL Injection** is a ^^code injection technique^^ used to attack data-driven applications, in which malicious SQL statements are inserted for execution.
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- It is a way of exploiting user input & SQL statements to compromise the database & retrieve sensitive data.
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-
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- ## Basic Terminology
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- What is **Cryptography**? #card
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card-last-interval:: 4
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card-repeats:: 1
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||||
card-ease-factor:: 2.6
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||||
card-next-schedule:: 2022-09-22T14:46:04.518Z
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||||
card-last-reviewed:: 2022-09-18T14:46:04.518Z
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card-last-score:: 5
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- **Cryptography** is the art of encompassing the principles & methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back into its original form.
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- What is **Plaintext**? #card
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card-last-interval:: 4
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card-repeats:: 1
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card-ease-factor:: 2.6
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||||
card-next-schedule:: 2022-09-22T14:39:41.558Z
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||||
card-last-reviewed:: 2022-09-18T14:39:41.558Z
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card-last-score:: 5
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- **Plaintext** is the ^^original, intelligible message.^^
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- What is **Ciphertext**? #card
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card-last-interval:: 4
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card-repeats:: 1
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||||
card-ease-factor:: 2.6
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||||
card-next-schedule:: 2022-09-22T14:39:52.620Z
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||||
card-last-reviewed:: 2022-09-18T14:39:52.621Z
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card-last-score:: 5
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- **Ciphertext** is the encrypted messsage.
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- What is a **Cipher**? #card
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card-last-interval:: 4
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||||
card-repeats:: 1
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||||
card-ease-factor:: 2.6
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||||
card-next-schedule:: 2022-09-22T14:44:53.575Z
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||||
card-last-reviewed:: 2022-09-18T14:44:53.575Z
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card-last-score:: 5
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- A **Cipher** is an algorithm for transforming an intelligible message into one that is unintelligible.
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- What is a **Key**? #card
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card-last-interval:: 4
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card-repeats:: 1
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||||
card-ease-factor:: 2.36
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||||
card-next-schedule:: 2022-09-22T14:43:53.075Z
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||||
card-last-reviewed:: 2022-09-18T14:43:53.075Z
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||||
card-last-score:: 3
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- A **Key** is some critical information used by the cipher, known only to the sender & receiver, selected from a **keyspace** (the set of all possible keys).
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- What does **Encipher** mean? #card
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card-last-interval:: 4
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||||
card-repeats:: 1
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||||
card-ease-factor:: 2.6
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||||
card-next-schedule:: 2022-09-22T14:46:57.114Z
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card-last-reviewed:: 2022-09-18T14:46:57.114Z
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card-last-score:: 5
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- **Enciphering** is the process of converting plaintext into ciphertext using a cipher & a key.
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- What does **Decipher** mean? #card
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card-last-interval:: 4
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card-repeats:: 1
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||||
card-ease-factor:: 2.6
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||||
card-next-schedule:: 2022-09-22T14:43:30.989Z
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card-last-reviewed:: 2022-09-18T14:43:30.989Z
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card-last-score:: 5
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- **Deciphering** is the process of converting ciphertext back into plaintext using a cipher & a key.
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- What is **Encryption**? #card
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card-last-interval:: 4
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card-repeats:: 1
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card-ease-factor:: 2.36
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||||
card-next-schedule:: 2022-09-22T14:44:36.754Z
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card-last-reviewed:: 2022-09-18T14:44:36.755Z
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card-last-score:: 3
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- **Encryption** is some mathematical function $E_K()$ mapping plaintext $P$ to ciphertext $C$ using the specified key $K$.
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- $$C=E_K(P)$$
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- What is **Decryption**? #card
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card-last-interval:: 4
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card-repeats:: 1
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card-ease-factor:: 2.36
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||||
card-next-schedule:: 2022-09-22T14:45:19.915Z
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card-last-reviewed:: 2022-09-18T14:45:19.915Z
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card-last-score:: 3
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- **Decryption** is some mathematical function ${E_K}^{-1}()$ mapping the ciphertext $C$ to plaintext $P$ using the specified key $K$.
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- $$P={E_K}^{-1}(C)$$
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- What is **Cryptanalysis**? #card
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card-last-interval:: 4
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card-repeats:: 1
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card-ease-factor:: 2.6
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card-next-schedule:: 2022-09-22T14:41:43.525Z
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card-last-reviewed:: 2022-09-18T14:41:43.525Z
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card-last-score:: 5
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- **Cryptanalysis** is the study of principles & methods of transforming an unintelligible message into an intelligible message without knowledge of the key.
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- What is **Cryptology**? #card
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card-last-interval:: 4
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card-repeats:: 1
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card-ease-factor:: 2.36
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card-next-schedule:: 2022-09-22T14:39:33.475Z
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card-last-reviewed:: 2022-09-18T14:39:33.475Z
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card-last-score:: 3
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- **Cryptology** is the field encompassing both cryptography & cryptanalysis.
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-
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-
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- ## Model of Conventional Cryptosystem
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- {:height 304, :width 610}
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- ## Cryptanalysis via Letter Frequency Distribution
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- Human languages are **redundant** - letters are not equally commonly used.
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- In the **English** language:
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- **E** is by far the most common letter followed by T, R, N, I, O, A, and S.
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- Other letters like Z, J, K, Q, and X are fairly rare.
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- Certain letter combinations like **TH** are quite common.
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- 
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-
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- ### C Program for Frequency Analysis of single Characters
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- ```c
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#include <stdio.h>
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#include <string.h>
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#include <ctype.h>
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int main(int argc, char* argv[]) {
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FILE* fp;
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int data[26];
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char c;
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memset(data, 0, siezof(data));
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if (argc != 2) {
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return(-1);
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}
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if (fp = fopen(argv[1], "r" == NULL)) {
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return(-2);
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}
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while(!feof(fp)) {
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c = toupper(fgetc(fp));
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if ((c >= 'A') && (c <= 'Z')) {
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data[c-65]++;
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}
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}
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for (int i = 0; i < 26; i++) {
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printf("%c:%i\n", i+65, data[i]);
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}
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fclose(fp);
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return(0);
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}
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```
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- ## Known Plaintext Attacks (KPA)
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- What is a **Known Plaintext Attack (KPA)**? #card
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card-last-interval:: 4
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||||
card-repeats:: 1
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||||
card-ease-factor:: 2.36
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||||
card-next-schedule:: 2022-09-22T14:46:48.201Z
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||||
card-last-reviewed:: 2022-09-18T14:46:48.202Z
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||||
card-last-score:: 3
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- The **Known Plaintext Attack (KPA)** is an attack model for cryptanalysis where the attacker has access to both:
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- some of, or all of, the plaintext (called a **crib**)
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- the ciphertext
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-
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-
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- ## Caesar Cipher
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- What is a **Caesar Cipher**? #card
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card-last-interval:: 4
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||||
card-repeats:: 1
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||||
card-ease-factor:: 2.6
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||||
card-next-schedule:: 2022-09-22T14:44:47.075Z
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||||
card-last-reviewed:: 2022-09-18T14:44:47.075Z
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card-last-score:: 5
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- A **Caesar Cipher** involves using an offset alphabet to encrypt a message.
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- We can use any shift from 1 to 25 to replace each plaintext letter with a letter a fixed distance away.
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- The **key letter** represents the start of this offset alphabet.
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- For example, a key letter of F means that A -> F, B -> G, and so on.
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- ## Playfair Cipher
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- Not even the large number of keys in a monoalphabetic cipher provides security.
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- What is a **monoalphabetic cipher**? #card
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card-last-interval:: 4
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||||
card-repeats:: 1
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||||
card-ease-factor:: 2.6
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||||
card-next-schedule:: 2022-09-22T14:40:09.236Z
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||||
card-last-reviewed:: 2022-09-18T14:40:09.237Z
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card-last-score:: 5
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- A **monoalphabetic cipher** is any cipher in which the letters of the plaintext are mapped to ciphertext letters based on a single alphabetic key.
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- One approach to improving security over monoalphabetic ciphers is to to encrypt ^^multiple letters.^^
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- The **Playfair Cipher** is one example of such an approach.
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- The algorithm was invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair.
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- ### How does the Playfair Cipher work? #card
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card-last-interval:: -1
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||||
card-repeats:: 1
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||||
card-ease-factor:: 2.5
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||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
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||||
card-last-reviewed:: 2022-09-18T14:43:16.213Z
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card-last-score:: 1
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- 
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- 1. Create a 5x5 grid of letters; insert the keyword as shown, with each letter only considered once; fill the grid with the remaining letters in alphabetic order.
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- 2. The letters are then encrypted in pairs.
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- 3. Repeats have an "X" inserted.
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- BALLOON -> BA LX LO ON
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- 4. Letters that fall in the same row are replaced with the letter on the right.
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- OK -> GM
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- 5. Letters in the same column are replaced with the letter below.
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- FO -> OU
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- 6. Otherwise, each letter gets replaced by the letter in its row but in the other letters column.
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- QM -> TH
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- ### Security of the Playfair Cipher
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- The security is much improved over simple monoalphabetic ciphers, as the Playfair Cipher has $26^2 = 676$ combinations.
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- This requires a 676 entry frequency table to analyse (as compared to a 26 entry frequency table for a monoalphabetic cipher) and correspondingly, more ciphertext.
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- However, the Playfair Cipher *can* be cracked through frequency analysis of letter pairs, given a few hundred letters.
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-
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- ## Vigenère Cipher
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- [Blaise de Vigenère](https://en.wikipedia.org/wiki/Blaise_de_Vigen%C3%A8re) is generally credited as the inventor of the **Polyalphabetic Substitution Cipher**.
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- What is a **Polyalphabetic Substitution Cipher**? #card
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card-last-interval:: 4
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||||
card-repeats:: 1
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||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:39:24.910Z
|
||||
card-last-reviewed:: 2022-09-18T14:39:24.912Z
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||||
card-last-score:: 5
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||||
- A **Polyalphabetic Substitution Cipher** uses multiple substitution alphabets, as opposed to a monoalphabetic cipher which uses a single alphabetic key.
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- The Vigenère Cipher improves security by using many monoalphabetic substitution alphabets, so each letter can be replaced by many others.
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- You use a **key** to select which alphabet is used for each letter of the message.
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- The $i^{th}$ letter of the key specifies the $i^{th}$ alphabet to use.
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- Use each alphabet in turn.
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- Repeat from the start after the end of the key is reached.
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-
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- ### Vigenère Steps
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- 
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- 1. Write the plaintext out, and write the keyword underneath it, repeated, for the length of the plaintext.
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- 2. Use each key letter in turn as a Caesar cipher key.
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- 3. Encrypt the corresponding plaintext letter.
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- In this example, we use the keyword "CIPHER". Hence, we have the following translation alphabets:
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- 
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- ### How to crack the Vigenère Cipher
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- 1. Search the ciphertext for repeated strings of letters - the longer the string, the better.
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- 2. For each occurrence of a repeated string, count how many letters are between the first letters in the string, and add one.
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- 3. Factorise that number.
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- 4. Repeat this process with each repeated string you find and make a table of common factors. The most common factor, $n$ is most likely the length of the keyword used to encipher the ciphertext.
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- 5. Do a frequency count on the ciphertext, on every $n^{th}$ letter. You should end up with $n$ different frequency counts.
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- 6. Compare these counts to standard frequency tables to figure out how much each letter was shifted by.
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- 7. Undo the shifts and read the message.
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- ## Enigma (Rotor Ciphers)
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- ### Rotor Ciphers
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- The mechanisation / automation of encryption.
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- An $\text{N}$-stage polyalphabetic algorithm modulo 26.
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- $26^N$ steps before a repetition, where $N$ is the number of cylinders.
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- The Enigma machine had 5 cylinders, so:
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- $$26^{N=5}=11,881,376 \text{ steps}$$
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-
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- ### Breaking Enigma using **Cribs**
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- The starting point for breaking Enigma was based on the following:
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- Plaintext messages were likely to contain certain phrases.
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- Weather reports contained the term "WETTER VORHERSAGE".
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- Military units often sent messages containing "KEINE BESONDEREN EREIGNISSE" ("nothing to report").
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- A plaintext letter was never mapped onto the same ciphertext letter.
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- While the cryptanalysts in Bletchely Park did not know exactly where these cribs were placed in an intercepted message, they could exclude certain positions.
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- 
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- From here, possible rotor start positions & rotor wiring would be systematically examined using the "bombe" - an electromechanical device designed by Turing that replicated the action of several Enigma machines wired together.
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-
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- ## Transposition Ciphers
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- What are **Transposition Ciphers**? #card
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||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:46:25.289Z
|
||||
card-last-score:: 1
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- **Transposition** or **Permutation Ciphers** hide the message by rearranging the letter order ^^without altering the actual letters used.^^
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- This can be recognised since the ciphertext has the same frequency distribution as the original text.
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- ### Rail Fence Cipher
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- Write plaintext letters out diagonally over a number of rows, then read off the cipher row by row.
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- 
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- ### Row Transposition Cipher
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||||
- What are **Row Transposition Ciphers**? #card
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||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:41:09.367Z
|
||||
card-last-score:: 1
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- **Row Transposition Ciphers** are a more complex kind of transposition cipher than Rail Fence Ciphers.
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- Plaintext letters are written out in rows over a specified number of columns.
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- The columns are then re-ordered according to some key before reading off the columns
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- 
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-
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- ## Product Ciphers
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- Ciphers using just substitutions or transpositions are not secure because of language characteristics.
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- Consider using several ciphers in succession to make it harder to crack:
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- Two substitutions make a more complex substitution.
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- Two transpositions make a more complex transposition.
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- However, a substitution followed by a transposition makes a much harder cipher.
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-
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-
|
||||
- # Steganography
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||||
- What is **Steganography**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:45:30.141Z
|
||||
card-last-reviewed:: 2022-09-18T14:45:30.142Z
|
||||
card-last-score:: 5
|
||||
- **Steganography** is an alternative to encryption that hides the existence of the message.
|
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- For example:
|
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- Using only a subset of letters / words in a message marked in some way.
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- Using invisible ink.
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- Hiding in LSB in graphic image or sound file.
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- The drawback of steganography is that it's not very economical in terms of overheads to hide a message.
|
||||
-
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||||
@ -0,0 +1,315 @@
|
||||
- #[[CT255 - Next Generation Technologies II]]
|
||||
- **Previous Topic:** [[GDPR]]
|
||||
- **Next Topic:** null
|
||||
- **Relevant Slides:** 
|
||||
id:: 63265db7-1d41-44f7-b4cf-0bab377a7c1c
|
||||
-
|
||||
- ## SQL Injections
|
||||
- What is an **SQL Injection**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-22T14:46:36.580Z
|
||||
card-last-reviewed:: 2022-09-18T14:46:36.581Z
|
||||
card-last-score:: 3
|
||||
- An **SQL Injection** is a ^^code injection technique^^ used to attack data-driven applications, in which malicious SQL statements are inserted for execution.
|
||||
- It is a way of exploiting user input & SQL statements to compromise the database & retrieve sensitive data.
|
||||
-
|
||||
- ## Basic Terminology
|
||||
- What is **Cryptography**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:46:04.518Z
|
||||
card-last-reviewed:: 2022-09-18T14:46:04.518Z
|
||||
card-last-score:: 5
|
||||
- **Cryptography** is the art of encompassing the principles & methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back into its original form.
|
||||
- What is **Plaintext**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:39:41.558Z
|
||||
card-last-reviewed:: 2022-09-18T14:39:41.558Z
|
||||
card-last-score:: 5
|
||||
- **Plaintext** is the ^^original, intelligible message.^^
|
||||
- What is **Ciphertext**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:39:52.620Z
|
||||
card-last-reviewed:: 2022-09-18T14:39:52.621Z
|
||||
card-last-score:: 5
|
||||
- **Ciphertext** is the encrypted messsage.
|
||||
- What is a **Cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:44:53.575Z
|
||||
card-last-reviewed:: 2022-09-18T14:44:53.575Z
|
||||
card-last-score:: 5
|
||||
- A **Cipher** is an algorithm for transforming an intelligible message into one that is unintelligible.
|
||||
- What is a **Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-22T14:43:53.075Z
|
||||
card-last-reviewed:: 2022-09-18T14:43:53.075Z
|
||||
card-last-score:: 3
|
||||
- A **Key** is some critical information used by the cipher, known only to the sender & receiver, selected from a **keyspace** (the set of all possible keys).
|
||||
- What does **Encipher** mean? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:46:57.114Z
|
||||
card-last-reviewed:: 2022-09-18T14:46:57.114Z
|
||||
card-last-score:: 5
|
||||
- **Enciphering** is the process of converting plaintext into ciphertext using a cipher & a key.
|
||||
- What does **Decipher** mean? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:43:30.989Z
|
||||
card-last-reviewed:: 2022-09-18T14:43:30.989Z
|
||||
card-last-score:: 5
|
||||
- **Deciphering** is the process of converting ciphertext back into plaintext using a cipher & a key.
|
||||
- What is **Encryption**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-22T14:44:36.754Z
|
||||
card-last-reviewed:: 2022-09-18T14:44:36.755Z
|
||||
card-last-score:: 3
|
||||
- **Encryption** is some mathematical function $E_K()$ mapping plaintext $P$ to ciphertext $C$ using the specified key $K$.
|
||||
- $$C=E_K(P)$$
|
||||
- What is **Decryption**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-22T14:45:19.915Z
|
||||
card-last-reviewed:: 2022-09-18T14:45:19.915Z
|
||||
card-last-score:: 3
|
||||
- **Decryption** is some mathematical function ${E_K}^{-1}()$ mapping the ciphertext $C$ to plaintext $P$ using the specified key $K$.
|
||||
- $$P={E_K}^{-1}(C)$$
|
||||
- What is **Cryptanalysis**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:41:43.525Z
|
||||
card-last-reviewed:: 2022-09-18T14:41:43.525Z
|
||||
card-last-score:: 5
|
||||
- **Cryptanalysis** is the study of principles & methods of transforming an unintelligible message into an intelligible message without knowledge of the key.
|
||||
- What is **Cryptology**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-22T14:39:33.475Z
|
||||
card-last-reviewed:: 2022-09-18T14:39:33.475Z
|
||||
card-last-score:: 3
|
||||
- **Cryptology** is the field encompassing both cryptography & cryptanalysis.
|
||||
-
|
||||
-
|
||||
- ## Model of Conventional Cryptosystem
|
||||
- {:height 304, :width 610}
|
||||
- ## Cryptanalysis via Letter Frequency Distribution
|
||||
- Human languages are **redundant** - letters are not equally commonly used.
|
||||
- In the **English** language:
|
||||
- **E** is by far the most common letter followed by T, R, N, I, O, A, and S.
|
||||
- Other letters like Z, J, K, Q, and X are fairly rare.
|
||||
- Certain letter combinations like **TH** are quite common.
|
||||
- 
|
||||
-
|
||||
- ### C Program for Frequency Analysis of single Characters
|
||||
- ```c
|
||||
#include <stdio.h>
|
||||
#include <string.h>
|
||||
#include <ctype.h>
|
||||
|
||||
int main(int argc, char* argv[]) {
|
||||
FILE* fp;
|
||||
int data[26];
|
||||
char c;
|
||||
|
||||
memset(data, 0, siezof(data));
|
||||
|
||||
if (argc != 2) {
|
||||
return(-1);
|
||||
}
|
||||
if (fp = fopen(argv[1], "r" == NULL)) {
|
||||
return(-2);
|
||||
}
|
||||
|
||||
while(!feof(fp)) {
|
||||
c = toupper(fgetc(fp));
|
||||
|
||||
if ((c >= 'A') && (c <= 'Z')) {
|
||||
data[c-65]++;
|
||||
}
|
||||
}
|
||||
|
||||
for (int i = 0; i < 26; i++) {
|
||||
printf("%c:%i\n", i+65, data[i]);
|
||||
}
|
||||
|
||||
fclose(fp);
|
||||
return(0);
|
||||
}
|
||||
```
|
||||
- ## Known Plaintext Attacks (KPA)
|
||||
- What is a **Known Plaintext Attack (KPA)**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-22T14:46:48.201Z
|
||||
card-last-reviewed:: 2022-09-18T14:46:48.202Z
|
||||
card-last-score:: 3
|
||||
- The **Known Plaintext Attack (KPA)** is an attack model for cryptanalysis where the attacker has access to both:
|
||||
- some of, or all of, the plaintext (called a **crib**)
|
||||
- the ciphertext
|
||||
-
|
||||
-
|
||||
- ## Caesar Cipher
|
||||
- What is a **Caesar Cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:44:47.075Z
|
||||
card-last-reviewed:: 2022-09-18T14:44:47.075Z
|
||||
card-last-score:: 5
|
||||
- A **Caesar Cipher** involves using an offset alphabet to encrypt a message.
|
||||
- We can use any shift from 1 to 25 to replace each plaintext letter with a letter a fixed distance away.
|
||||
- The **key letter** represents the start of this offset alphabet.
|
||||
- For example, a key letter of F means that A -> F, B -> G, and so on.
|
||||
- ## Playfair Cipher
|
||||
- Not even the large number of keys in a monoalphabetic cipher provides security.
|
||||
- What is a **monoalphabetic cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:40:09.236Z
|
||||
card-last-reviewed:: 2022-09-18T14:40:09.237Z
|
||||
card-last-score:: 5
|
||||
- A **monoalphabetic cipher** is any cipher in which the letters of the plaintext are mapped to ciphertext letters based on a single alphabetic key.
|
||||
- One approach to improving security over monoalphabetic ciphers is to to encrypt ^^multiple letters.^^
|
||||
- The **Playfair Cipher** is one example of such an approach.
|
||||
- The algorithm was invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair.
|
||||
- ### How does the Playfair Cipher work? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:43:16.213Z
|
||||
card-last-score:: 1
|
||||
- 
|
||||
- 1. Create a 5x5 grid of letters; insert the keyword as shown, with each letter only considered once; fill the grid with the remaining letters in alphabetic order.
|
||||
- 2. The letters are then encrypted in pairs.
|
||||
- 3. Repeats have an "X" inserted.
|
||||
- BALLOON -> BA LX LO ON
|
||||
- 4. Letters that fall in the same row are replaced with the letter on the right.
|
||||
- OK -> GM
|
||||
- 5. Letters in the same column are replaced with the letter below.
|
||||
- FO -> OU
|
||||
- 6. Otherwise, each letter gets replaced by the letter in its row but in the other letters column.
|
||||
- QM -> TH
|
||||
- ### Security of the Playfair Cipher
|
||||
- The security is much improved over simple monoalphabetic ciphers, as the Playfair Cipher has $26^2 = 676$ combinations.
|
||||
- This requires a 676 entry frequency table to analyse (as compared to a 26 entry frequency table for a monoalphabetic cipher) and correspondingly, more ciphertext.
|
||||
- However, the Playfair Cipher *can* be cracked through frequency analysis of letter pairs, given a few hundred letters.
|
||||
-
|
||||
- ## Vigenère Cipher
|
||||
- [Blaise de Vigenère](https://en.wikipedia.org/wiki/Blaise_de_Vigen%C3%A8re) is generally credited as the inventor of the **Polyalphabetic Substitution Cipher**.
|
||||
- What is a **Polyalphabetic Substitution Cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:39:24.910Z
|
||||
card-last-reviewed:: 2022-09-18T14:39:24.912Z
|
||||
card-last-score:: 5
|
||||
- A **Polyalphabetic Substitution Cipher** uses multiple substitution alphabets, as opposed to a monoalphabetic cipher which uses a single alphabetic key.
|
||||
- The Vigenère Cipher improves security by using many monoalphabetic substitution alphabets, so each letter can be replaced by many others.
|
||||
- You use a **key** to select which alphabet is used for each letter of the message.
|
||||
- The $i^{th}$ letter of the key specifies the $i^{th}$ alphabet to use.
|
||||
- Use each alphabet in turn.
|
||||
- Repeat from the start after the end of the key is reached.
|
||||
-
|
||||
- ### Vigenère Steps
|
||||
- 
|
||||
- 1. Write the plaintext out, and write the keyword underneath it, repeated, for the length of the plaintext.
|
||||
- 2. Use each key letter in turn as a Caesar cipher key.
|
||||
- 3. Encrypt the corresponding plaintext letter.
|
||||
- In this example, we use the keyword "CIPHER". Hence, we have the following translation alphabets:
|
||||
- 
|
||||
- ### How to crack the Vigenère Cipher
|
||||
- 1. Search the ciphertext for repeated strings of letters - the longer the string, the better.
|
||||
- 2. For each occurrence of a repeated string, count how many letters are between the first letters in the string, and add one.
|
||||
- 3. Factorise that number.
|
||||
- 4. Repeat this process with each repeated string you find and make a table of common factors. The most common factor, $n$ is most likely the length of the keyword used to encipher the ciphertext.
|
||||
- 5. Do a frequency count on the ciphertext, on every $n^{th}$ letter. You should end up with $n$ different frequency counts.
|
||||
- 6. Compare these counts to standard frequency tables to figure out how much each letter was shifted by.
|
||||
- 7. Undo the shifts and read the message.
|
||||
- ## Enigma (Rotor Ciphers)
|
||||
- ### Rotor Ciphers
|
||||
- The mechanisation / automation of encryption.
|
||||
- An $\text{N}$-stage polyalphabetic algorithm modulo 26.
|
||||
- $26^N$ steps before a repetition, where $N$ is the number of cylinders.
|
||||
- The Enigma machine had 5 cylinders, so:
|
||||
- $$26^{N=5}=11,881,376 \text{ steps}$$
|
||||
-
|
||||
- ### Breaking Enigma using **Cribs**
|
||||
- The starting point for breaking Enigma was based on the following:
|
||||
- Plaintext messages were likely to contain certain phrases.
|
||||
- Weather reports contained the term "WETTER VORHERSAGE".
|
||||
- Military units often sent messages containing "KEINE BESONDEREN EREIGNISSE" ("nothing to report").
|
||||
- A plaintext letter was never mapped onto the same ciphertext letter.
|
||||
- While the cryptanalysts in Bletchely Park did not know exactly where these cribs were placed in an intercepted message, they could exclude certain positions.
|
||||
- 
|
||||
- From here, possible rotor start positions & rotor wiring would be systematically examined using the "bombe" - an electromechanical device designed by Turing that replicated the action of several Enigma machines wired together.
|
||||
-
|
||||
- ## Transposition Ciphers
|
||||
- What are **Transposition Ciphers**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:46:25.289Z
|
||||
card-last-score:: 1
|
||||
- **Transposition** or **Permutation Ciphers** hide the message by rearranging the letter order ^^without altering the actual letters used.^^
|
||||
- This can be recognised since the ciphertext has the same frequency distribution as the original text.
|
||||
- ### Rail Fence Cipher
|
||||
- Write plaintext letters out diagonally over a number of rows, then read off the cipher row by row.
|
||||
- 
|
||||
- ### Row Transposition Cipher
|
||||
- What are **Row Transposition Ciphers**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:41:09.367Z
|
||||
card-last-score:: 1
|
||||
- **Row Transposition Ciphers** are a more complex kind of transposition cipher than Rail Fence Ciphers.
|
||||
- Plaintext letters are written out in rows over a specified number of columns.
|
||||
- The columns are then re-ordered according to some key before reading off the columns
|
||||
- 
|
||||
-
|
||||
- ## Product Ciphers
|
||||
- Ciphers using just substitutions or transpositions are not secure because of language characteristics.
|
||||
- Consider using several ciphers in succession to make it harder to crack:
|
||||
- Two substitutions make a more complex substitution.
|
||||
- Two transpositions make a more complex transposition.
|
||||
- However, a substitution followed by a transposition makes a much harder cipher.
|
||||
-
|
||||
-
|
||||
- # Steganography
|
||||
- What is **Steganography**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-22T14:45:30.141Z
|
||||
card-last-reviewed:: 2022-09-18T14:45:30.142Z
|
||||
card-last-score:: 5
|
||||
- **Steganography** is an alternative to encryption that hides the existence of the message.
|
||||
- For example:
|
||||
- Using only a subset of letters / words in a message marked in some way.
|
||||
- Using invisible ink.
|
||||
- Hiding in LSB in graphic image or sound file.
|
||||
- The drawback of steganography is that it's not very economical in terms of overheads to hide a message.
|
||||
-
|
||||
@ -0,0 +1,316 @@
|
||||
- #[[CT255 - Next Generation Technologies II]]
|
||||
- **Previous Topic:** [[GDPR]]
|
||||
- **Next Topic:** [[Human Security & Passwords]]
|
||||
- **Relevant Slides:** 
|
||||
id:: 63265db7-1d41-44f7-b4cf-0bab377a7c1c
|
||||
-
|
||||
- ## SQL Injections
|
||||
- What is an **SQL Injection**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-10-08T12:29:41.822Z
|
||||
card-last-reviewed:: 2022-10-04T12:29:41.822Z
|
||||
card-last-score:: 5
|
||||
-
|
||||
- An **SQL Injection** is a ^^code injection technique^^ used to attack data-driven applications, in which malicious SQL statements are inserted for execution.
|
||||
- It is a way of exploiting user input & SQL statements to compromise the database & retrieve sensitive data.
|
||||
-
|
||||
- ## Basic Terminology
|
||||
- What is **Cryptography**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:13:18.768Z
|
||||
card-last-reviewed:: 2022-09-30T12:13:18.768Z
|
||||
card-last-score:: 5
|
||||
- **Cryptography** is the art of encompassing the principles & methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back into its original form.
|
||||
- What is **Plaintext**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:07:59.453Z
|
||||
card-last-reviewed:: 2022-09-30T12:07:59.456Z
|
||||
card-last-score:: 5
|
||||
- **Plaintext** is the ^^original, intelligible message.^^
|
||||
- What is **Ciphertext**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T08:29:48.663Z
|
||||
card-last-reviewed:: 2022-09-30T08:29:48.663Z
|
||||
card-last-score:: 5
|
||||
- **Ciphertext** is the encrypted messsage.
|
||||
- What is a **Cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-10-04T12:11:06.873Z
|
||||
card-last-reviewed:: 2022-09-30T12:11:06.874Z
|
||||
card-last-score:: 3
|
||||
- A **Cipher** is an algorithm for transforming an intelligible message into one that is unintelligible.
|
||||
- What is a **Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-10-04T12:09:48.972Z
|
||||
card-last-reviewed:: 2022-09-30T12:09:48.972Z
|
||||
card-last-score:: 5
|
||||
- A **Key** is some critical information used by the cipher, known only to the sender & receiver, selected from a **keyspace** (the set of all possible keys).
|
||||
- What does **Encipher** mean? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:13:23.717Z
|
||||
card-last-reviewed:: 2022-09-30T12:13:23.717Z
|
||||
card-last-score:: 5
|
||||
- **Enciphering** is the process of converting plaintext into ciphertext using a cipher & a key.
|
||||
- What does **Decipher** mean?
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:09:14.829Z
|
||||
card-last-reviewed:: 2022-09-30T12:09:14.829Z
|
||||
card-last-score:: 5
|
||||
- **Deciphering** is the process of converting ciphertext back into plaintext using a cipher & a key.
|
||||
- What is **Encryption**? #card
|
||||
card-last-score:: 5
|
||||
card-repeats:: 2
|
||||
card-next-schedule:: 2022-10-04T12:09:55.038Z
|
||||
card-last-interval:: 4
|
||||
card-ease-factor:: 2.46
|
||||
card-last-reviewed:: 2022-09-30T12:09:55.039Z
|
||||
- **Encryption** is some mathematical function $E_K()$ mapping plaintext $P$ to ciphertext $C$ using the specified key $K$.
|
||||
- $$C=E_K(P)$$
|
||||
- What is **Decryption**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.22
|
||||
card-next-schedule:: 2022-10-04T12:13:15.777Z
|
||||
card-last-reviewed:: 2022-09-30T12:13:15.777Z
|
||||
card-last-score:: 3
|
||||
- **Decryption** is some mathematical function ${E_K}^{-1}()$ mapping the ciphertext $C$ to plaintext $P$ using the specified key $K$.
|
||||
- $$P={E_K}^{-1}(C)$$
|
||||
- What is **Cryptanalysis**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:08:29.141Z
|
||||
card-last-reviewed:: 2022-09-30T12:08:29.141Z
|
||||
card-last-score:: 5
|
||||
- **Cryptanalysis** is the study of principles & methods of transforming an unintelligible message into an intelligible message without knowledge of the key.
|
||||
- What is **Cryptology**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.22
|
||||
card-next-schedule:: 2022-10-04T09:29:41.789Z
|
||||
card-last-reviewed:: 2022-09-30T09:29:41.789Z
|
||||
card-last-score:: 3
|
||||
- **Cryptology** is the field encompassing both cryptography & cryptanalysis.
|
||||
-
|
||||
-
|
||||
- ## Model of Conventional Cryptosystem
|
||||
- {:height 304, :width 610}
|
||||
- ## Cryptanalysis via Letter Frequency Distribution
|
||||
- Human languages are **redundant** - letters are not equally commonly used.
|
||||
- In the **English** language:
|
||||
- **E** is by far the most common letter followed by T, R, N, I, O, A, and S.
|
||||
- Other letters like Z, J, K, Q, and X are fairly rare.
|
||||
- Certain letter combinations like **TH** are quite common.
|
||||
- 
|
||||
-
|
||||
- ### C Program for Frequency Analysis of single Characters
|
||||
- ```c
|
||||
#include <stdio.h>
|
||||
#include <string.h>
|
||||
#include <ctype.h>
|
||||
|
||||
int main(int argc, char* argv[]) {
|
||||
FILE* fp;
|
||||
int data[26];
|
||||
char c;
|
||||
|
||||
memset(data, 0, siezof(data));
|
||||
|
||||
if (argc != 2) {
|
||||
return(-1);
|
||||
}
|
||||
if (fp = fopen(argv[1], "r" == NULL)) {
|
||||
return(-2);
|
||||
}
|
||||
|
||||
while(!feof(fp)) {
|
||||
c = toupper(fgetc(fp));
|
||||
|
||||
if ((c >= 'A') && (c <= 'Z')) {
|
||||
data[c-65]++;
|
||||
}
|
||||
}
|
||||
|
||||
for (int i = 0; i < 26; i++) {
|
||||
printf("%c:%i\n", i+65, data[i]);
|
||||
}
|
||||
|
||||
fclose(fp);
|
||||
return(0);
|
||||
}
|
||||
```
|
||||
- ## Known Plaintext Attacks (KPA)
|
||||
- What is a **Known Plaintext Attack (KPA)**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-16T14:39:41.014Z
|
||||
card-last-reviewed:: 2022-10-06T09:39:41.014Z
|
||||
card-last-score:: 5
|
||||
- The **Known Plaintext Attack (KPA)** is an attack model for cryptanalysis where the attacker has access to both:
|
||||
- some of, or all of, the plaintext (called a **crib**)
|
||||
- the ciphertext
|
||||
-
|
||||
-
|
||||
- ## Caesar Cipher
|
||||
- What is a **Caesar Cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:09:58.027Z
|
||||
card-last-reviewed:: 2022-09-30T12:09:58.027Z
|
||||
card-last-score:: 5
|
||||
- A **Caesar Cipher** involves using an offset alphabet to encrypt a message.
|
||||
- We can use any shift from 1 to 25 to replace each plaintext letter with a letter a fixed distance away.
|
||||
- The **key letter** represents the start of this offset alphabet.
|
||||
- For example, a key letter of F means that A -> F, B -> G, and so on.
|
||||
- ## Playfair Cipher
|
||||
- Not even the large number of keys in a monoalphabetic cipher provides security.
|
||||
- What is a **monoalphabetic cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:08:03.733Z
|
||||
card-last-reviewed:: 2022-09-30T12:08:03.733Z
|
||||
card-last-score:: 5
|
||||
- A **monoalphabetic cipher** is any cipher in which the letters of the plaintext are mapped to ciphertext letters based on a single alphabetic key.
|
||||
- One approach to improving security over monoalphabetic ciphers is to to encrypt ^^multiple letters.^^
|
||||
- The **Playfair Cipher** is one example of such an approach.
|
||||
- The algorithm was invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair.
|
||||
- ### How does the Playfair Cipher work?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 2
|
||||
card-next-schedule:: 2022-10-08T00:33:19.557Z
|
||||
card-last-interval:: 3.51
|
||||
card-ease-factor:: 2.6
|
||||
card-last-reviewed:: 2022-10-04T12:33:19.558Z
|
||||
- 
|
||||
- 1. Create a 5x5 grid of letters; insert the keyword as shown, with each letter only considered once; fill the grid with the remaining letters in alphabetic order.
|
||||
- 2. The letters are then encrypted in pairs.
|
||||
- 3. Repeats have an "X" inserted.
|
||||
- BALLOON -> BA LX LO ON
|
||||
- 4. Letters that fall in the same row are replaced with the letter on the right.
|
||||
- OK -> GM
|
||||
- 5. Letters in the same column are replaced with the letter below.
|
||||
- FO -> OU
|
||||
- 6. Otherwise, each letter gets replaced by the letter in its row but in the other letters column.
|
||||
- QM -> TH
|
||||
- ### Security of the Playfair Cipher
|
||||
- The security is much improved over simple monoalphabetic ciphers, as the Playfair Cipher has $26^2 = 676$ combinations.
|
||||
- This requires a 676 entry frequency table to analyse (as compared to a 26 entry frequency table for a monoalphabetic cipher) and correspondingly, more ciphertext.
|
||||
- However, the Playfair Cipher *can* be cracked through frequency analysis of letter pairs, given a few hundred letters.
|
||||
-
|
||||
- ## Vigenère Cipher
|
||||
- [Blaise de Vigenère](https://en.wikipedia.org/wiki/Blaise_de_Vigen%C3%A8re) is generally credited as the inventor of the **Polyalphabetic Substitution Cipher**.
|
||||
- What is a **Polyalphabetic Substitution Cipher**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-30T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-30T09:29:32.337Z
|
||||
card-last-score:: 1
|
||||
- A **Polyalphabetic Substitution Cipher** uses multiple substitution alphabets, as opposed to a monoalphabetic cipher which uses a single alphabetic key.
|
||||
- The Vigenère Cipher improves security by using many monoalphabetic substitution alphabets, so each letter can be replaced by many others.
|
||||
- You use a **key** to select which alphabet is used for each letter of the message.
|
||||
- The $i^{th}$ letter of the key specifies the $i^{th}$ alphabet to use.
|
||||
- Use each alphabet in turn.
|
||||
- Repeat from the start after the end of the key is reached.
|
||||
-
|
||||
- ### Vigenère Steps
|
||||
- 
|
||||
- 1. Write the plaintext out, and write the keyword underneath it, repeated, for the length of the plaintext.
|
||||
- 2. Use each key letter in turn as a Caesar cipher key.
|
||||
- 3. Encrypt the corresponding plaintext letter.
|
||||
- In this example, we use the keyword "CIPHER". Hence, we have the following translation alphabets:
|
||||
- 
|
||||
- ### How to crack the Vigenère Cipher
|
||||
- 1. Search the ciphertext for repeated strings of letters - the longer the string, the better.
|
||||
- 2. For each occurrence of a repeated string, count how many letters are between the first letters in the string, and add one.
|
||||
- 3. Factorise that number.
|
||||
- 4. Repeat this process with each repeated string you find and make a table of common factors. The most common factor, $n$ is most likely the length of the keyword used to encipher the ciphertext.
|
||||
- 5. Do a frequency count on the ciphertext, on every $n^{th}$ letter. You should end up with $n$ different frequency counts.
|
||||
- 6. Compare these counts to standard frequency tables to figure out how much each letter was shifted by.
|
||||
- 7. Undo the shifts and read the message.
|
||||
- ## Enigma (Rotor Ciphers)
|
||||
- ### Rotor Ciphers
|
||||
- The mechanisation / automation of encryption.
|
||||
- An $\text{N}$-stage polyalphabetic algorithm modulo 26.
|
||||
- $26^N$ steps before a repetition, where $N$ is the number of cylinders.
|
||||
- The Enigma machine had 5 cylinders, so:
|
||||
- $$26^{N=5}=11,881,376 \text{ steps}$$
|
||||
-
|
||||
- ### Breaking Enigma using **Cribs**
|
||||
- The starting point for breaking Enigma was based on the following:
|
||||
- Plaintext messages were likely to contain certain phrases.
|
||||
- Weather reports contained the term "WETTER VORHERSAGE".
|
||||
- Military units often sent messages containing "KEINE BESONDEREN EREIGNISSE" ("nothing to report").
|
||||
- A plaintext letter was never mapped onto the same ciphertext letter.
|
||||
- While the cryptanalysts in Bletchely Park did not know exactly where these cribs were placed in an intercepted message, they could exclude certain positions.
|
||||
- 
|
||||
- From here, possible rotor start positions & rotor wiring would be systematically examined using the "bombe" - an electromechanical device designed by Turing that replicated the action of several Enigma machines wired together.
|
||||
-
|
||||
- ## Transposition Ciphers
|
||||
- What are **Transposition Ciphers**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-10-04T09:08:18.147Z
|
||||
card-last-reviewed:: 2022-09-30T09:08:18.150Z
|
||||
card-last-score:: 3
|
||||
- **Transposition** or **Permutation Ciphers** hide the message by rearranging the letter order ^^without altering the actual letters used.^^
|
||||
- This can be recognised since the ciphertext has the same frequency distribution as the original text.
|
||||
- ### Rail Fence Cipher
|
||||
- Write plaintext letters out diagonally over a number of rows, then read off the cipher row by row.
|
||||
- 
|
||||
- ### Row Transposition Cipher
|
||||
- What are **Row Transposition Ciphers**? #card
|
||||
card-last-interval:: 3.45
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-10-03T19:11:23.311Z
|
||||
card-last-reviewed:: 2022-09-30T09:11:23.312Z
|
||||
card-last-score:: 3
|
||||
- **Row Transposition Ciphers** are a more complex kind of transposition cipher than Rail Fence Ciphers.
|
||||
- Plaintext letters are written out in rows over a specified number of columns.
|
||||
- The columns are then re-ordered according to some key before reading off the columns
|
||||
- 
|
||||
-
|
||||
- ## Product Ciphers
|
||||
- Ciphers using just substitutions or transpositions are not secure because of language characteristics.
|
||||
- Consider using several ciphers in succession to make it harder to crack:
|
||||
- Two substitutions make a more complex substitution.
|
||||
- Two transpositions make a more complex transposition.
|
||||
- However, a substitution followed by a transposition makes a much harder cipher.
|
||||
-
|
||||
-
|
||||
- # Steganography
|
||||
- What is **Steganography**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-08T12:33:34.285Z
|
||||
card-last-reviewed:: 2022-10-04T12:33:34.285Z
|
||||
card-last-score:: 5
|
||||
- **Steganography** is an alternative to encryption that hides the existence of the message.
|
||||
- For example:
|
||||
- Using only a subset of letters / words in a message marked in some way.
|
||||
- Using invisible ink.
|
||||
- Hiding in LSB in graphic image or sound file.
|
||||
- The drawback of steganography is that it's not very economical in terms of overheads to hide a message.
|
||||
-
|
||||
@ -0,0 +1,316 @@
|
||||
- #[[CT255 - Next Generation Technologies II]]
|
||||
- **Previous Topic:** [[GDPR]]
|
||||
- **Next Topic:** [[Human Security & Passwords]]
|
||||
- **Relevant Slides:** 
|
||||
id:: 63265db7-1d41-44f7-b4cf-0bab377a7c1c
|
||||
-
|
||||
- ## SQL Injections
|
||||
- What is an **SQL Injection**? #card
|
||||
card-last-interval:: 10.6
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-19T12:58:54.850Z
|
||||
card-last-reviewed:: 2022-10-08T22:58:54.851Z
|
||||
card-last-score:: 5
|
||||
-
|
||||
- An **SQL Injection** is a ***code injection technique*** used to attack data-driven applications, in which malicious SQL statements are inserted for execution.
|
||||
- It is a way of exploiting user input & SQL statements to compromise the database & retrieve sensitive data.
|
||||
-
|
||||
- ## Basic Terminology
|
||||
- What is **Cryptography**? #card
|
||||
card-last-interval:: 33.64
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2022-11-10T01:19:02.918Z
|
||||
card-last-reviewed:: 2022-10-07T10:19:02.918Z
|
||||
card-last-score:: 5
|
||||
- **Cryptography** is the art of encompassing the principles & methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back into its original form.
|
||||
- What is **Plaintext**?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-17T21:24:55.999Z
|
||||
card-last-interval:: 11.2
|
||||
card-ease-factor:: 2.8
|
||||
card-last-reviewed:: 2022-10-06T17:24:55.999Z
|
||||
- **Plaintext** is the ^^original, intelligible message.^^
|
||||
- What is **Ciphertext**?
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-18T14:39:00.206Z
|
||||
card-last-reviewed:: 2022-10-07T10:39:00.207Z
|
||||
card-last-score:: 5
|
||||
- **Ciphertext** is the encrypted messsage.
|
||||
- What is a **Cipher**? #card
|
||||
card-last-interval:: 4.14
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-13T01:43:58.055Z
|
||||
card-last-reviewed:: 2022-10-08T22:43:58.056Z
|
||||
card-last-score:: 5
|
||||
- A **Cipher** is an algorithm for transforming an intelligible message into one that is unintelligible.
|
||||
- What is a **Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-11T10:47:20.304Z
|
||||
card-last-reviewed:: 2022-10-07T10:47:20.304Z
|
||||
card-last-score:: 3
|
||||
- A **Key** is some critical information used by the cipher, known only to the sender & receiver, selected from a **keyspace** (the set of all possible keys).
|
||||
- What does **Encipher** mean?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-17T21:14:43.789Z
|
||||
card-last-interval:: 11.2
|
||||
card-ease-factor:: 2.8
|
||||
card-last-reviewed:: 2022-10-06T17:14:43.790Z
|
||||
- **Enciphering** is the process of converting plaintext into ciphertext using a cipher & a key.
|
||||
- What does **Decipher** mean?
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:09:14.829Z
|
||||
card-last-reviewed:: 2022-09-30T12:09:14.829Z
|
||||
card-last-score:: 5
|
||||
- **Deciphering** is the process of converting ciphertext back into plaintext using a cipher & a key.
|
||||
- What is **Encryption**? #card
|
||||
card-last-score:: 3
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-16T16:40:50.413Z
|
||||
card-last-interval:: 9.28
|
||||
card-ease-factor:: 2.32
|
||||
card-last-reviewed:: 2022-10-07T10:40:50.414Z
|
||||
- **Encryption** is some mathematical function $E_K()$ mapping plaintext $P$ to ciphertext $C$ using the specified key $K$.
|
||||
- $$E_K(P) = C$$
|
||||
- What is **Decryption**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.22
|
||||
card-next-schedule:: 2022-10-08T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-10-08T15:22:54.739Z
|
||||
card-last-score:: 1
|
||||
- **Decryption** is some mathematical function ${E_K}^{-1}()$ mapping the ciphertext $C$ to plaintext $P$ using the specified key $K$.
|
||||
- $$P={E_K}^{-1}(C)$$
|
||||
- What is **Cryptanalysis**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-17T21:28:14.325Z
|
||||
card-last-reviewed:: 2022-10-06T17:28:14.325Z
|
||||
card-last-score:: 5
|
||||
- **Cryptanalysis** is the study of principles & methods of transforming an unintelligible message into an intelligible message without knowledge of the key.
|
||||
- What is **Cryptology**?
|
||||
card-last-interval:: 9.28
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-16T16:40:03.776Z
|
||||
card-last-reviewed:: 2022-10-07T10:40:03.777Z
|
||||
card-last-score:: 5
|
||||
- **Cryptology** is the field encompassing both cryptography & cryptanalysis.
|
||||
-
|
||||
-
|
||||
- ## Model of Conventional Cryptosystem
|
||||
- {:height 304, :width 610}
|
||||
- ## Cryptanalysis via Letter Frequency Distribution
|
||||
- Human languages are **redundant** - letters are not equally commonly used.
|
||||
- In the **English** language:
|
||||
- **E** is by far the most common letter followed by T, R, N, I, O, A, and S.
|
||||
- Other letters like Z, J, K, Q, and X are fairly rare.
|
||||
- Certain letter combinations like **TH** are quite common.
|
||||
- 
|
||||
-
|
||||
- ### C Program for Frequency Analysis of single Characters
|
||||
- ```c
|
||||
#include <stdio.h>
|
||||
#include <string.h>
|
||||
#include <ctype.h>
|
||||
|
||||
int main(int argc, char* argv[]) {
|
||||
FILE* fp;
|
||||
int data[26];
|
||||
char c;
|
||||
|
||||
memset(data, 0, siezof(data));
|
||||
|
||||
if (argc != 2) {
|
||||
return(-1);
|
||||
}
|
||||
if (fp = fopen(argv[1], "r" == NULL)) {
|
||||
return(-2);
|
||||
}
|
||||
|
||||
while(!feof(fp)) {
|
||||
c = toupper(fgetc(fp));
|
||||
|
||||
if ((c >= 'A') && (c <= 'Z')) {
|
||||
data[c-65]++;
|
||||
}
|
||||
}
|
||||
|
||||
for (int i = 0; i < 26; i++) {
|
||||
printf("%c:%i\n", i+65, data[i]);
|
||||
}
|
||||
|
||||
fclose(fp);
|
||||
return(0);
|
||||
}
|
||||
```
|
||||
- ## Known Plaintext Attacks (KPA)
|
||||
- What is a **Known Plaintext Attack (KPA)**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-16T14:39:41.014Z
|
||||
card-last-reviewed:: 2022-10-06T09:39:41.014Z
|
||||
card-last-score:: 5
|
||||
- The **Known Plaintext Attack (KPA)** is an attack model for cryptanalysis where the attacker has access to both:
|
||||
- some of, or all of, the plaintext (called a **crib**)
|
||||
- the ciphertext
|
||||
-
|
||||
-
|
||||
- ## Caesar Cipher
|
||||
- What is a **Caesar Cipher**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-17T21:27:16.902Z
|
||||
card-last-reviewed:: 2022-10-06T17:27:16.903Z
|
||||
card-last-score:: 5
|
||||
- A **Caesar Cipher** involves using an offset alphabet to encrypt a message.
|
||||
- We can use any shift from 1 to 25 to replace each plaintext letter with a letter a fixed distance away.
|
||||
- The **key letter** represents the start of this offset alphabet.
|
||||
- For example, a key letter of F means that A -> F, B -> G, and so on.
|
||||
- ## Playfair Cipher
|
||||
- Not even the large number of keys in a monoalphabetic cipher provides security.
|
||||
- What is a **monoalphabetic cipher**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-16T22:27:13.914Z
|
||||
card-last-reviewed:: 2022-10-06T17:27:13.915Z
|
||||
card-last-score:: 3
|
||||
- A **monoalphabetic cipher** is any cipher in which the letters of the plaintext are mapped to ciphertext letters based on a single alphabetic key.
|
||||
- One approach to improving security over monoalphabetic ciphers is to to encrypt ^^multiple letters.^^
|
||||
- The **Playfair Cipher** is one example of such an approach.
|
||||
- The algorithm was invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair.
|
||||
- ### How does the Playfair Cipher work?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 2
|
||||
card-next-schedule:: 2022-10-08T00:33:19.557Z
|
||||
card-last-interval:: 3.51
|
||||
card-ease-factor:: 2.6
|
||||
card-last-reviewed:: 2022-10-04T12:33:19.558Z
|
||||
- 
|
||||
- 1. Create a 5x5 grid of letters; insert the keyword as shown, with each letter only considered once; fill the grid with the remaining letters in alphabetic order.
|
||||
- 2. The letters are then encrypted in pairs.
|
||||
- 3. Repeats have an "X" inserted.
|
||||
- BALLOON -> BA LX LO ON
|
||||
- 4. Letters that fall in the same row are replaced with the letter on the right.
|
||||
- OK -> GM
|
||||
- 5. Letters in the same column are replaced with the letter below.
|
||||
- FO -> OU
|
||||
- 6. Otherwise, each letter gets replaced by the letter in its row but in the other letters column.
|
||||
- QM -> TH
|
||||
- ### Security of the Playfair Cipher
|
||||
- The security is much improved over simple monoalphabetic ciphers, as the Playfair Cipher has $26^2 = 676$ combinations.
|
||||
- This requires a 676 entry frequency table to analyse (as compared to a 26 entry frequency table for a monoalphabetic cipher) and correspondingly, more ciphertext.
|
||||
- However, the Playfair Cipher *can* be cracked through frequency analysis of letter pairs, given a few hundred letters.
|
||||
-
|
||||
- ## Vigenère Cipher
|
||||
- [Blaise de Vigenère](https://en.wikipedia.org/wiki/Blaise_de_Vigen%C3%A8re) is generally credited as the inventor of the **Polyalphabetic Substitution Cipher**.
|
||||
- What is a **Polyalphabetic Substitution Cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-11T10:31:42.282Z
|
||||
card-last-reviewed:: 2022-10-07T10:31:42.283Z
|
||||
card-last-score:: 5
|
||||
- A **Polyalphabetic Substitution Cipher** uses multiple substitution alphabets, as opposed to a monoalphabetic cipher which uses a single alphabetic key.
|
||||
- The Vigenère Cipher improves security by using many monoalphabetic substitution alphabets, so each letter can be replaced by many others.
|
||||
- You use a **key** to select which alphabet is used for each letter of the message.
|
||||
- The $i^{th}$ letter of the key specifies the $i^{th}$ alphabet to use.
|
||||
- Use each alphabet in turn.
|
||||
- Repeat from the start after the end of the key is reached.
|
||||
-
|
||||
- ### Vigenère Steps
|
||||
- 
|
||||
- 1. Write the plaintext out, and write the keyword underneath it, repeated, for the length of the plaintext.
|
||||
- 2. Use each key letter in turn as a Caesar cipher key.
|
||||
- 3. Encrypt the corresponding plaintext letter.
|
||||
- In this example, we use the keyword "CIPHER". Hence, we have the following translation alphabets:
|
||||
- 
|
||||
- ### How to crack the Vigenère Cipher
|
||||
- 1. Search the ciphertext for repeated strings of letters - the longer the string, the better.
|
||||
- 2. For each occurrence of a repeated string, count how many letters are between the first letters in the string, and add one.
|
||||
- 3. Factorise that number.
|
||||
- 4. Repeat this process with each repeated string you find and make a table of common factors. The most common factor, $n$ is most likely the length of the keyword used to encipher the ciphertext.
|
||||
- 5. Do a frequency count on the ciphertext, on every $n^{th}$ letter. You should end up with $n$ different frequency counts.
|
||||
- 6. Compare these counts to standard frequency tables to figure out how much each letter was shifted by.
|
||||
- 7. Undo the shifts and read the message.
|
||||
- ## Enigma (Rotor Ciphers)
|
||||
- ### Rotor Ciphers
|
||||
- The mechanisation / automation of encryption.
|
||||
- An $\text{N}$-stage polyalphabetic algorithm modulo 26.
|
||||
- $26^N$ steps before a repetition, where $N$ is the number of cylinders.
|
||||
- The Enigma machine had 5 cylinders, so:
|
||||
- $$26^{N=5}=11,881,376 \text{ steps}$$
|
||||
-
|
||||
- ### Breaking Enigma using **Cribs**
|
||||
- The starting point for breaking Enigma was based on the following:
|
||||
- Plaintext messages were likely to contain certain phrases.
|
||||
- Weather reports contained the term "WETTER VORHERSAGE".
|
||||
- Military units often sent messages containing "KEINE BESONDEREN EREIGNISSE" ("nothing to report").
|
||||
- A plaintext letter was never mapped onto the same ciphertext letter.
|
||||
- While the cryptanalysts in Bletchely Park did not know exactly where these cribs were placed in an intercepted message, they could exclude certain positions.
|
||||
- 
|
||||
- From here, possible rotor start positions & rotor wiring would be systematically examined using the "bombe" - an electromechanical device designed by Turing that replicated the action of several Enigma machines wired together.
|
||||
-
|
||||
- ## Transposition Ciphers
|
||||
- What are **Transposition Ciphers**? #card
|
||||
card-last-interval:: 8.88
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.22
|
||||
card-next-schedule:: 2022-10-16T07:39:25.895Z
|
||||
card-last-reviewed:: 2022-10-07T10:39:25.895Z
|
||||
card-last-score:: 3
|
||||
- **Transposition** or **Permutation Ciphers** hide the message by rearranging the letter order ^^without altering the actual letters used.^^
|
||||
- This can be recognised since the ciphertext has the same frequency distribution as the original text.
|
||||
- ### Rail Fence Cipher
|
||||
- Write plaintext letters out diagonally over a number of rows, then read off the cipher row by row.
|
||||
- 
|
||||
- ### Row Transposition Cipher
|
||||
- What are **Row Transposition Ciphers**? #card
|
||||
card-last-interval:: 26.21
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-11-01T22:18:29.590Z
|
||||
card-last-reviewed:: 2022-10-06T17:18:29.591Z
|
||||
card-last-score:: 5
|
||||
- **Row Transposition Ciphers** are a more complex kind of transposition cipher than Rail Fence Ciphers.
|
||||
- Plaintext letters are written out in rows over a specified number of columns.
|
||||
- The columns are then re-ordered according to some key before reading off the columns
|
||||
- 
|
||||
-
|
||||
- ## Product Ciphers
|
||||
- Ciphers using just substitutions or transpositions are not secure because of language characteristics.
|
||||
- Consider using several ciphers in succession to make it harder to crack:
|
||||
- Two substitutions make a more complex substitution.
|
||||
- Two transpositions make a more complex transposition.
|
||||
- However, a substitution followed by a transposition makes a much harder cipher.
|
||||
-
|
||||
-
|
||||
- # Steganography
|
||||
- What is **Steganography**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-20T12:50:18.491Z
|
||||
card-last-reviewed:: 2022-10-09T08:50:18.492Z
|
||||
card-last-score:: 5
|
||||
- **Steganography** is an alternative to encryption that hides the existence of the message.
|
||||
- For example:
|
||||
- Using only a subset of letters / words in a message marked in some way.
|
||||
- Using invisible ink.
|
||||
- Hiding in LSB in graphic image or sound file.
|
||||
- The drawback of steganography is that it's not very economical in terms of overheads to hide a message.
|
||||
-
|
||||
@ -0,0 +1,316 @@
|
||||
- #[[CT255 - Next Generation Technologies II]]
|
||||
- **Previous Topic:** [[GDPR]]
|
||||
- **Next Topic:** [[Human Security & Passwords]]
|
||||
- **Relevant Slides:** 
|
||||
id:: 63265db7-1d41-44f7-b4cf-0bab377a7c1c
|
||||
-
|
||||
- ## SQL Injections
|
||||
- What is an **SQL Injection**? #card
|
||||
card-last-interval:: 10.6
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-19T12:58:54.850Z
|
||||
card-last-reviewed:: 2022-10-08T22:58:54.851Z
|
||||
card-last-score:: 5
|
||||
-
|
||||
- An **SQL Injection** is a ***code injection technique*** used to attack data-driven applications, in which malicious SQL statements are inserted for execution.
|
||||
- It is a way of exploiting user input & SQL statements to compromise the database & retrieve sensitive data.
|
||||
-
|
||||
- ## Basic Terminology
|
||||
- What is **Cryptography**? #card
|
||||
card-last-interval:: 33.64
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2022-11-10T01:19:02.918Z
|
||||
card-last-reviewed:: 2022-10-07T10:19:02.918Z
|
||||
card-last-score:: 5
|
||||
- **Cryptography** is the art of encompassing the principles & methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back into its original form.
|
||||
- What is **Plaintext**?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-17T21:24:55.999Z
|
||||
card-last-interval:: 11.2
|
||||
card-ease-factor:: 2.8
|
||||
card-last-reviewed:: 2022-10-06T17:24:55.999Z
|
||||
- **Plaintext** is the ^^original, intelligible message.^^
|
||||
- What is **Ciphertext**?
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-18T14:39:00.206Z
|
||||
card-last-reviewed:: 2022-10-07T10:39:00.207Z
|
||||
card-last-score:: 5
|
||||
- **Ciphertext** is the encrypted messsage.
|
||||
- What is a **Cipher**? #card
|
||||
card-last-interval:: 4.14
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-13T01:43:58.055Z
|
||||
card-last-reviewed:: 2022-10-08T22:43:58.056Z
|
||||
card-last-score:: 5
|
||||
- A **Cipher** is an algorithm for transforming an intelligible message into one that is unintelligible.
|
||||
- What is a **Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-11T10:47:20.304Z
|
||||
card-last-reviewed:: 2022-10-07T10:47:20.304Z
|
||||
card-last-score:: 3
|
||||
- A **Key** is some critical information used by the cipher, known only to the sender & receiver, selected from a **keyspace** (the set of all possible keys).
|
||||
- What does **Encipher** mean?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-17T21:14:43.789Z
|
||||
card-last-interval:: 11.2
|
||||
card-ease-factor:: 2.8
|
||||
card-last-reviewed:: 2022-10-06T17:14:43.790Z
|
||||
- **Enciphering** is the process of converting plaintext into ciphertext using a cipher & a key.
|
||||
- What does **Decipher** mean?
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:09:14.829Z
|
||||
card-last-reviewed:: 2022-09-30T12:09:14.829Z
|
||||
card-last-score:: 5
|
||||
- **Deciphering** is the process of converting ciphertext back into plaintext using a cipher & a key.
|
||||
- What is **Encryption**? #card
|
||||
card-last-score:: 3
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-16T16:40:50.413Z
|
||||
card-last-interval:: 9.28
|
||||
card-ease-factor:: 2.32
|
||||
card-last-reviewed:: 2022-10-07T10:40:50.414Z
|
||||
- **Encryption** is some mathematical function $E_K()$ mapping plaintext $P$ to ciphertext $C$ using the specified key $K$.
|
||||
- $$E_K(P) = C$$
|
||||
- What is **Decryption**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-14T11:37:04.045Z
|
||||
card-last-reviewed:: 2022-10-10T11:37:04.046Z
|
||||
card-last-score:: 5
|
||||
- **Decryption** is some mathematical function ${E_K}^{-1}()$ mapping the ciphertext $C$ to plaintext $P$ using the specified key $K$.
|
||||
- $$P={E_K}^{-1}(C)$$
|
||||
- What is **Cryptanalysis**? #card
|
||||
card-last-interval:: 28.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-11-16T15:43:11.780Z
|
||||
card-last-reviewed:: 2022-10-19T08:43:11.781Z
|
||||
card-last-score:: 3
|
||||
- **Cryptanalysis** is the study of principles & methods of transforming an unintelligible message into an intelligible message without knowledge of the key.
|
||||
- What is **Cryptology**?
|
||||
card-last-interval:: 9.28
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-16T16:40:03.776Z
|
||||
card-last-reviewed:: 2022-10-07T10:40:03.777Z
|
||||
card-last-score:: 5
|
||||
- **Cryptology** is the field encompassing both cryptography & cryptanalysis.
|
||||
-
|
||||
-
|
||||
- ## Model of Conventional Cryptosystem
|
||||
- {:height 304, :width 610}
|
||||
- ## Cryptanalysis via Letter Frequency Distribution
|
||||
- Human languages are **redundant** - letters are not equally commonly used.
|
||||
- In the **English** language:
|
||||
- **E** is by far the most common letter followed by T, R, N, I, O, A, and S.
|
||||
- Other letters like Z, J, K, Q, and X are fairly rare.
|
||||
- Certain letter combinations like **TH** are quite common.
|
||||
- 
|
||||
-
|
||||
- ### C Program for Frequency Analysis of single Characters
|
||||
- ```c
|
||||
#include <stdio.h>
|
||||
#include <string.h>
|
||||
#include <ctype.h>
|
||||
|
||||
int main(int argc, char* argv[]) {
|
||||
FILE* fp;
|
||||
int data[26];
|
||||
char c;
|
||||
|
||||
memset(data, 0, siezof(data));
|
||||
|
||||
if (argc != 2) {
|
||||
return(-1);
|
||||
}
|
||||
if (fp = fopen(argv[1], "r" == NULL)) {
|
||||
return(-2);
|
||||
}
|
||||
|
||||
while(!feof(fp)) {
|
||||
c = toupper(fgetc(fp));
|
||||
|
||||
if ((c >= 'A') && (c <= 'Z')) {
|
||||
data[c-65]++;
|
||||
}
|
||||
}
|
||||
|
||||
for (int i = 0; i < 26; i++) {
|
||||
printf("%c:%i\n", i+65, data[i]);
|
||||
}
|
||||
|
||||
fclose(fp);
|
||||
return(0);
|
||||
}
|
||||
```
|
||||
- ## Known Plaintext Attacks (KPA)
|
||||
- What is a **Known Plaintext Attack (KPA)**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-16T14:39:41.014Z
|
||||
card-last-reviewed:: 2022-10-06T09:39:41.014Z
|
||||
card-last-score:: 5
|
||||
- The **Known Plaintext Attack (KPA)** is an attack model for cryptanalysis where the attacker has access to both:
|
||||
- some of, or all of, the plaintext (called a **crib**)
|
||||
- the ciphertext
|
||||
-
|
||||
-
|
||||
- ## Caesar Cipher
|
||||
- What is a **Caesar Cipher**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-17T21:27:16.902Z
|
||||
card-last-reviewed:: 2022-10-06T17:27:16.903Z
|
||||
card-last-score:: 5
|
||||
- A **Caesar Cipher** involves using an offset alphabet to encrypt a message.
|
||||
- We can use any shift from 1 to 25 to replace each plaintext letter with a letter a fixed distance away.
|
||||
- The **key letter** represents the start of this offset alphabet.
|
||||
- For example, a key letter of F means that A -> F, B -> G, and so on.
|
||||
- ## Playfair Cipher
|
||||
- Not even the large number of keys in a monoalphabetic cipher provides security.
|
||||
- What is a **monoalphabetic cipher**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-16T22:27:13.914Z
|
||||
card-last-reviewed:: 2022-10-06T17:27:13.915Z
|
||||
card-last-score:: 3
|
||||
- A **monoalphabetic cipher** is any cipher in which the letters of the plaintext are mapped to ciphertext letters based on a single alphabetic key.
|
||||
- One approach to improving security over monoalphabetic ciphers is to to encrypt ^^multiple letters.^^
|
||||
- The **Playfair Cipher** is one example of such an approach.
|
||||
- The algorithm was invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair.
|
||||
- ### How does the Playfair Cipher work?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 2
|
||||
card-next-schedule:: 2022-10-08T00:33:19.557Z
|
||||
card-last-interval:: 3.51
|
||||
card-ease-factor:: 2.6
|
||||
card-last-reviewed:: 2022-10-04T12:33:19.558Z
|
||||
- 
|
||||
- 1. Create a 5x5 grid of letters; insert the keyword as shown, with each letter only considered once; fill the grid with the remaining letters in alphabetic order.
|
||||
- 2. The letters are then encrypted in pairs.
|
||||
- 3. Repeats have an "X" inserted.
|
||||
- BALLOON -> BA LX LO ON
|
||||
- 4. Letters that fall in the same row are replaced with the letter on the right.
|
||||
- OK -> GM
|
||||
- 5. Letters in the same column are replaced with the letter below.
|
||||
- FO -> OU
|
||||
- 6. Otherwise, each letter gets replaced by the letter in its row but in the other letters column.
|
||||
- QM -> TH
|
||||
- ### Security of the Playfair Cipher
|
||||
- The security is much improved over simple monoalphabetic ciphers, as the Playfair Cipher has $26^2 = 676$ combinations.
|
||||
- This requires a 676 entry frequency table to analyse (as compared to a 26 entry frequency table for a monoalphabetic cipher) and correspondingly, more ciphertext.
|
||||
- However, the Playfair Cipher *can* be cracked through frequency analysis of letter pairs, given a few hundred letters.
|
||||
-
|
||||
- ## Vigenère Cipher
|
||||
- [Blaise de Vigenère](https://en.wikipedia.org/wiki/Blaise_de_Vigen%C3%A8re) is generally credited as the inventor of the **Polyalphabetic Substitution Cipher**.
|
||||
- What is a **Polyalphabetic Substitution Cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-11T10:31:42.282Z
|
||||
card-last-reviewed:: 2022-10-07T10:31:42.283Z
|
||||
card-last-score:: 5
|
||||
- A **Polyalphabetic Substitution Cipher** uses multiple substitution alphabets, as opposed to a monoalphabetic cipher which uses a single alphabetic key.
|
||||
- The Vigenère Cipher improves security by using many monoalphabetic substitution alphabets, so each letter can be replaced by many others.
|
||||
- You use a **key** to select which alphabet is used for each letter of the message.
|
||||
- The $i^{th}$ letter of the key specifies the $i^{th}$ alphabet to use.
|
||||
- Use each alphabet in turn.
|
||||
- Repeat from the start after the end of the key is reached.
|
||||
-
|
||||
- ### Vigenère Steps
|
||||
- 
|
||||
- 1. Write the plaintext out, and write the keyword underneath it, repeated, for the length of the plaintext.
|
||||
- 2. Use each key letter in turn as a Caesar cipher key.
|
||||
- 3. Encrypt the corresponding plaintext letter.
|
||||
- In this example, we use the keyword "CIPHER". Hence, we have the following translation alphabets:
|
||||
- 
|
||||
- ### How to crack the Vigenère Cipher
|
||||
- 1. Search the ciphertext for repeated strings of letters - the longer the string, the better.
|
||||
- 2. For each occurrence of a repeated string, count how many letters are between the first letters in the string, and add one.
|
||||
- 3. Factorise that number.
|
||||
- 4. Repeat this process with each repeated string you find and make a table of common factors. The most common factor, $n$ is most likely the length of the keyword used to encipher the ciphertext.
|
||||
- 5. Do a frequency count on the ciphertext, on every $n^{th}$ letter. You should end up with $n$ different frequency counts.
|
||||
- 6. Compare these counts to standard frequency tables to figure out how much each letter was shifted by.
|
||||
- 7. Undo the shifts and read the message.
|
||||
- ## Enigma (Rotor Ciphers)
|
||||
- ### Rotor Ciphers
|
||||
- The mechanisation / automation of encryption.
|
||||
- An $\text{N}$-stage polyalphabetic algorithm modulo 26.
|
||||
- $26^N$ steps before a repetition, where $N$ is the number of cylinders.
|
||||
- The Enigma machine had 5 cylinders, so:
|
||||
- $$26^{N=5}=11,881,376 \text{ steps}$$
|
||||
-
|
||||
- ### Breaking Enigma using **Cribs**
|
||||
- The starting point for breaking Enigma was based on the following:
|
||||
- Plaintext messages were likely to contain certain phrases.
|
||||
- Weather reports contained the term "WETTER VORHERSAGE".
|
||||
- Military units often sent messages containing "KEINE BESONDEREN EREIGNISSE" ("nothing to report").
|
||||
- A plaintext letter was never mapped onto the same ciphertext letter.
|
||||
- While the cryptanalysts in Bletchely Park did not know exactly where these cribs were placed in an intercepted message, they could exclude certain positions.
|
||||
- 
|
||||
- From here, possible rotor start positions & rotor wiring would be systematically examined using the "bombe" - an electromechanical device designed by Turing that replicated the action of several Enigma machines wired together.
|
||||
-
|
||||
- ## Transposition Ciphers
|
||||
- What are **Transposition Ciphers**? #card
|
||||
card-last-interval:: 8.88
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.22
|
||||
card-next-schedule:: 2022-10-16T07:39:25.895Z
|
||||
card-last-reviewed:: 2022-10-07T10:39:25.895Z
|
||||
card-last-score:: 3
|
||||
- **Transposition** or **Permutation Ciphers** hide the message by rearranging the letter order ^^without altering the actual letters used.^^
|
||||
- This can be recognised since the ciphertext has the same frequency distribution as the original text.
|
||||
- ### Rail Fence Cipher
|
||||
- Write plaintext letters out diagonally over a number of rows, then read off the cipher row by row.
|
||||
- 
|
||||
- ### Row Transposition Cipher
|
||||
- What are **Row Transposition Ciphers**? #card
|
||||
card-last-interval:: 26.21
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-11-01T22:18:29.590Z
|
||||
card-last-reviewed:: 2022-10-06T17:18:29.591Z
|
||||
card-last-score:: 5
|
||||
- **Row Transposition Ciphers** are a more complex kind of transposition cipher than Rail Fence Ciphers.
|
||||
- Plaintext letters are written out in rows over a specified number of columns.
|
||||
- The columns are then re-ordered according to some key before reading off the columns
|
||||
- 
|
||||
-
|
||||
- ## Product Ciphers
|
||||
- Ciphers using just substitutions or transpositions are not secure because of language characteristics.
|
||||
- Consider using several ciphers in succession to make it harder to crack:
|
||||
- Two substitutions make a more complex substitution.
|
||||
- Two transpositions make a more complex transposition.
|
||||
- However, a substitution followed by a transposition makes a much harder cipher.
|
||||
-
|
||||
-
|
||||
- # Steganography
|
||||
- What is **Steganography**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-20T12:50:18.491Z
|
||||
card-last-reviewed:: 2022-10-09T08:50:18.492Z
|
||||
card-last-score:: 5
|
||||
- **Steganography** is an alternative to encryption that hides the existence of the message.
|
||||
- For example:
|
||||
- Using only a subset of letters / words in a message marked in some way.
|
||||
- Using invisible ink.
|
||||
- Hiding in LSB in graphic image or sound file.
|
||||
- The drawback of steganography is that it's not very economical in terms of overheads to hide a message.
|
||||
-
|
||||
@ -0,0 +1,317 @@
|
||||
- #[[CT255 - Next Generation Technologies II]]
|
||||
- **Previous Topic:** [[GDPR]]
|
||||
- **Next Topic:** [[Human Security & Passwords]]
|
||||
- **Relevant Slides:** 
|
||||
id:: 63265db7-1d41-44f7-b4cf-0bab377a7c1c
|
||||
-
|
||||
- ## SQL Injections
|
||||
- What is an **SQL Injection**? #card
|
||||
card-last-interval:: 10.6
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-19T12:58:54.850Z
|
||||
card-last-reviewed:: 2022-10-08T22:58:54.851Z
|
||||
card-last-score:: 5
|
||||
-
|
||||
- An **SQL Injection** is a ***code injection technique*** used to attack data-driven applications, in which malicious SQL statements are inserted for execution.
|
||||
- It is a way of exploiting user input & SQL statements to compromise the database & retrieve sensitive data.
|
||||
-
|
||||
- ## Basic Terminology
|
||||
- What is **Cryptography**? #card
|
||||
card-last-interval:: 33.64
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2022-11-10T01:19:02.918Z
|
||||
card-last-reviewed:: 2022-10-07T10:19:02.918Z
|
||||
card-last-score:: 5
|
||||
- **Cryptography** is the art of encompassing the principles & methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back into its original form.
|
||||
- What is **Plaintext**?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-17T21:24:55.999Z
|
||||
card-last-interval:: 11.2
|
||||
card-ease-factor:: 2.8
|
||||
card-last-reviewed:: 2022-10-06T17:24:55.999Z
|
||||
- **Plaintext** is the ^^original, intelligible message.^^
|
||||
- What is **Ciphertext**?
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-18T14:39:00.206Z
|
||||
card-last-reviewed:: 2022-10-07T10:39:00.207Z
|
||||
card-last-score:: 5
|
||||
- **Ciphertext** is the encrypted messsage.
|
||||
- What is a **Cipher**? #card
|
||||
card-last-interval:: 4.14
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-13T01:43:58.055Z
|
||||
card-last-reviewed:: 2022-10-08T22:43:58.056Z
|
||||
card-last-score:: 5
|
||||
- A **Cipher** is an algorithm for transforming an intelligible message into one that is unintelligible.
|
||||
- What is a **Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-11T10:47:20.304Z
|
||||
card-last-reviewed:: 2022-10-07T10:47:20.304Z
|
||||
card-last-score:: 3
|
||||
- A **Key** is some critical information used by the cipher, known only to the sender & receiver, selected from a **keyspace** (the set of all possible keys).
|
||||
- What does **Encipher** mean?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-17T21:14:43.789Z
|
||||
card-last-interval:: 11.2
|
||||
card-ease-factor:: 2.8
|
||||
card-last-reviewed:: 2022-10-06T17:14:43.790Z
|
||||
- **Enciphering** is the process of converting plaintext into ciphertext using a cipher & a key.
|
||||
- What does **Decipher** mean?
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-04T12:09:14.829Z
|
||||
card-last-reviewed:: 2022-09-30T12:09:14.829Z
|
||||
card-last-score:: 5
|
||||
- **Deciphering** is the process of converting ciphertext back into plaintext using a cipher & a key.
|
||||
- What is **Encryption**? #card
|
||||
card-last-score:: 3
|
||||
card-repeats:: 3
|
||||
card-next-schedule:: 2022-10-16T16:40:50.413Z
|
||||
card-last-interval:: 9.28
|
||||
card-ease-factor:: 2.32
|
||||
card-last-reviewed:: 2022-10-07T10:40:50.414Z
|
||||
- **Encryption** is some mathematical function $E_K()$ mapping plaintext $P$ to ciphertext $C$ using the specified key $K$.
|
||||
- $$E_K(P) = C$$
|
||||
- What is **Decryption**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-14T11:37:04.045Z
|
||||
card-last-reviewed:: 2022-10-10T11:37:04.046Z
|
||||
card-last-score:: 5
|
||||
- **Decryption** is some mathematical function ${E_K}^{-1}()$ mapping the ciphertext $C$ to plaintext $P$ using the specified key $K$.
|
||||
- $$P={E_K}^{-1}(C)$$
|
||||
- What is **Cryptanalysis**? #card
|
||||
card-last-interval:: 28.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-11-16T15:43:11.780Z
|
||||
card-last-reviewed:: 2022-10-19T08:43:11.781Z
|
||||
card-last-score:: 3
|
||||
- **Cryptanalysis** is the study of principles & methods of transforming an unintelligible message into an intelligible message without knowledge of the key.
|
||||
- What is **Cryptology**?
|
||||
card-last-interval:: 9.28
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-16T16:40:03.776Z
|
||||
card-last-reviewed:: 2022-10-07T10:40:03.777Z
|
||||
card-last-score:: 5
|
||||
- **Cryptology** is the field encompassing both cryptography & cryptanalysis.
|
||||
-
|
||||
-
|
||||
- ## Model of Conventional Cryptosystem
|
||||
- {:height 304, :width 610}
|
||||
- ## Cryptanalysis via Letter Frequency Distribution
|
||||
- Human languages are **redundant** - letters are not equally commonly used.
|
||||
- In the **English** language:
|
||||
- **E** is by far the most common letter followed by T, R, N, I, O, A, and S.
|
||||
- Other letters like Z, J, K, Q, and X are fairly rare.
|
||||
- Certain letter combinations like **TH** are quite common.
|
||||
- 
|
||||
-
|
||||
- ### C Program for Frequency Analysis of single Characters
|
||||
- ```c
|
||||
#include <stdio.h>
|
||||
#include <string.h>
|
||||
#include <ctype.h>
|
||||
|
||||
int main(int argc, char* argv[]) {
|
||||
FILE* fp;
|
||||
int data[26];
|
||||
char c;
|
||||
|
||||
memset(data, 0, siezof(data));
|
||||
|
||||
if (argc != 2) {
|
||||
return(-1);
|
||||
}
|
||||
if (fp = fopen(argv[1], "r" == NULL)) {
|
||||
return(-2);
|
||||
}
|
||||
|
||||
while(!feof(fp)) {
|
||||
c = toupper(fgetc(fp));
|
||||
|
||||
if ((c >= 'A') && (c <= 'Z')) {
|
||||
data[c-65]++;
|
||||
}
|
||||
}
|
||||
|
||||
for (int i = 0; i < 26; i++) {
|
||||
printf("%c:%i\n", i+65, data[i]);
|
||||
}
|
||||
|
||||
fclose(fp);
|
||||
return(0);
|
||||
}
|
||||
```
|
||||
- ## Known Plaintext Attacks (KPA)
|
||||
- What is a **Known Plaintext Attack (KPA)**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-16T14:39:41.014Z
|
||||
card-last-reviewed:: 2022-10-06T09:39:41.014Z
|
||||
card-last-score:: 5
|
||||
- The **Known Plaintext Attack (KPA)** is an attack model for cryptanalysis where the attacker has access to both:
|
||||
- some of, or all of, the plaintext (called a **crib**)
|
||||
- the ciphertext
|
||||
-
|
||||
-
|
||||
- ## Caesar Cipher
|
||||
- What is a **Caesar Cipher**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-17T21:27:16.902Z
|
||||
card-last-reviewed:: 2022-10-06T17:27:16.903Z
|
||||
card-last-score:: 5
|
||||
- A **Caesar Cipher** involves using an offset alphabet to encrypt a message.
|
||||
- We can use any shift from 1 to 25 to replace each plaintext letter with a letter a fixed distance away.
|
||||
- The **key letter** represents the start of this offset alphabet.
|
||||
- For example, a key letter of F means that A -> F, B -> G, and so on.
|
||||
- ## Playfair Cipher
|
||||
- Not even the large number of keys in a monoalphabetic cipher provides security.
|
||||
- What is a **monoalphabetic cipher**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-16T22:27:13.914Z
|
||||
card-last-reviewed:: 2022-10-06T17:27:13.915Z
|
||||
card-last-score:: 3
|
||||
- A **monoalphabetic cipher** is any cipher in which the letters of the plaintext are mapped to ciphertext letters based on a single alphabetic key.
|
||||
- One approach to improving security over monoalphabetic ciphers is to to encrypt ^^multiple letters.^^
|
||||
- The **Playfair Cipher** is one example of such an approach.
|
||||
- The algorithm was invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair.
|
||||
- ### How does the Playfair Cipher work?
|
||||
card-last-score:: 5
|
||||
card-repeats:: 2
|
||||
card-next-schedule:: 2022-10-08T00:33:19.557Z
|
||||
card-last-interval:: 3.51
|
||||
card-ease-factor:: 2.6
|
||||
card-last-reviewed:: 2022-10-04T12:33:19.558Z
|
||||
- 
|
||||
- 1. Create a 5x5 grid of letters; insert the keyword as shown, with each letter only considered once; fill the grid with the remaining letters in alphabetic order.
|
||||
- 2. The letters are then encrypted in pairs.
|
||||
- 3. Repeats have an "X" inserted.
|
||||
- BALLOON -> BA LX LO ON
|
||||
- 4. Letters that fall in the same row are replaced with the letter on the right.
|
||||
- OK -> GM
|
||||
- 5. Letters in the same column are replaced with the letter below.
|
||||
- FO -> OU
|
||||
- 6. Otherwise, each letter gets replaced by the letter in its row but in the other letters column.
|
||||
- QM -> TH
|
||||
- ### Security of the Playfair Cipher
|
||||
- The security is much improved over simple monoalphabetic ciphers, as the Playfair Cipher has $26^2 = 676$ combinations.
|
||||
- This requires a 676 entry frequency table to analyse (as compared to a 26 entry frequency table for a monoalphabetic cipher) and correspondingly, more ciphertext.
|
||||
- However, the Playfair Cipher *can* be cracked through frequency analysis of letter pairs, given a few hundred letters.
|
||||
-
|
||||
- ## Vigenère Cipher
|
||||
- [Blaise de Vigenère](https://en.wikipedia.org/wiki/Blaise_de_Vigen%C3%A8re) is generally credited as the inventor of the **Polyalphabetic Substitution Cipher**.
|
||||
- What is a **Polyalphabetic Substitution Cipher**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-11T10:31:42.282Z
|
||||
card-last-reviewed:: 2022-10-07T10:31:42.283Z
|
||||
card-last-score:: 5
|
||||
- A **Polyalphabetic Substitution Cipher** uses multiple substitution alphabets, as opposed to a monoalphabetic cipher which uses a single alphabetic key.
|
||||
- The Vigenère Cipher improves security by using many monoalphabetic substitution alphabets, so each letter can be replaced by many others.
|
||||
- You use a **key** to select which alphabet is used for each letter of the message.
|
||||
- The $i^{th}$ letter of the key specifies the $i^{th}$ alphabet to use.
|
||||
- Use each alphabet in turn.
|
||||
- Repeat from the start after the end of the key is reached.
|
||||
-
|
||||
- ### Vigenère Steps
|
||||
- 
|
||||
- 1. Write the plaintext out, and write the keyword underneath it, repeated, for the length of the plaintext.
|
||||
- 2. Use each key letter in turn as a Caesar cipher key.
|
||||
- 3. Encrypt the corresponding plaintext letter.
|
||||
- In this example, we use the keyword "CIPHER". Hence, we have the following translation alphabets:
|
||||
- 
|
||||
- ### How to crack the Vigenère Cipher
|
||||
- 1. Search the ciphertext for repeated strings of letters - the longer the string, the better.
|
||||
- 2. For each occurrence of a repeated string, count how many letters are between the first letters in the string, and add one.
|
||||
- 3. Factorise that number.
|
||||
- 4. Repeat this process with each repeated string you find and make a table of common factors. The most common factor, $n$ is most likely the length of the keyword used to encipher the ciphertext.
|
||||
- 5. Do a frequency count on the ciphertext, on every $n^{th}$ letter. You should end up with $n$ different frequency counts.
|
||||
- 6. Compare these counts to standard frequency tables to figure out how much each letter was shifted by.
|
||||
- 7. Undo the shifts and read the message.
|
||||
- ## Enigma (Rotor Ciphers)
|
||||
- ### Rotor Ciphers
|
||||
- The mechanisation / automation of encryption.
|
||||
- An $\text{N}$-stage polyalphabetic algorithm modulo 26.
|
||||
- $26^N$ steps before a repetition, where $N$ is the number of cylinders.
|
||||
- The Enigma machine had 5 cylinders, so:
|
||||
- $$26^{N=5}=11,881,376 \text{ steps}$$
|
||||
-
|
||||
- ### Breaking Enigma using **Cribs**
|
||||
- The starting point for breaking Enigma was based on the following:
|
||||
- Plaintext messages were likely to contain certain phrases.
|
||||
- Weather reports contained the term "WETTER VORHERSAGE".
|
||||
- Military units often sent messages containing "KEINE BESONDEREN EREIGNISSE" ("nothing to report").
|
||||
- A plaintext letter was never mapped onto the same ciphertext letter.
|
||||
- While the cryptanalysts in Bletchely Park did not know exactly where these cribs were placed in an intercepted message, they could exclude certain positions.
|
||||
- 
|
||||
- From here, possible rotor start positions & rotor wiring would be systematically examined using the "bombe" - an electromechanical device designed by Turing that replicated the action of several Enigma machines wired together.
|
||||
-
|
||||
- ## Transposition Ciphers
|
||||
- What are **Transposition Ciphers**? #card
|
||||
card-last-interval:: 8.88
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.22
|
||||
card-next-schedule:: 2022-10-16T07:39:25.895Z
|
||||
card-last-reviewed:: 2022-10-07T10:39:25.895Z
|
||||
card-last-score:: 3
|
||||
- **Transposition** or **Permutation Ciphers** hide the message by rearranging the letter order ^^without altering the actual letters used.^^
|
||||
- This can be recognised since the ciphertext has the same frequency distribution as the original text.
|
||||
- ### Rail Fence Cipher
|
||||
id:: 6344093b-2f4f-4c58-95e4-39a8b30d16c3
|
||||
- Write plaintext letters out diagonally over a number of rows, then read off the cipher row by row.
|
||||
- 
|
||||
- ### Row Transposition Cipher
|
||||
- What are **Row Transposition Ciphers**? #card
|
||||
card-last-interval:: 26.21
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-11-01T22:18:29.590Z
|
||||
card-last-reviewed:: 2022-10-06T17:18:29.591Z
|
||||
card-last-score:: 5
|
||||
- **Row Transposition Ciphers** are a more complex kind of transposition cipher than ((6344093b-2f4f-4c58-95e4-39a8b30d16c3))s.
|
||||
- Plaintext letters are written out in rows over a specified number of columns.
|
||||
- The columns are then re-ordered according to some key before reading off the columns
|
||||
- 
|
||||
-
|
||||
- ## Product Ciphers
|
||||
- Ciphers using just substitutions or transpositions are not secure because of language characteristics.
|
||||
- Consider using several ciphers in succession to make it harder to crack:
|
||||
- Two substitutions make a more complex substitution.
|
||||
- Two transpositions make a more complex transposition.
|
||||
- However, a substitution followed by a transposition makes a much harder cipher.
|
||||
-
|
||||
-
|
||||
- # Steganography
|
||||
- What is **Steganography**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-20T12:50:18.491Z
|
||||
card-last-reviewed:: 2022-10-09T08:50:18.492Z
|
||||
card-last-score:: 5
|
||||
- **Steganography** is an alternative to encryption that hides the existence of the message.
|
||||
- For example:
|
||||
- Using only a subset of letters / words in a message marked in some way.
|
||||
- Using invisible ink.
|
||||
- Hiding in LSB in graphic image or sound file.
|
||||
- The drawback of steganography is that it's not very economical in terms of overheads to hide a message.
|
||||
-
|
||||
Reference in New Issue
Block a user