- #[[CT255 - Next Generation Technologies II]]
- **Previous Topic:** [[Block Ciphers & Stream Ciphers]]
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- **Relevant Slides:** ![ct255_09.pdf](../assets/ct255_09_1668712193123_0.pdf)
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- There are four types of attacks in the context of communication across a network, which are addressed by message authentication:
	- Masquerade (insertion of messages into the network from a fraudulent source).
	- Content modification.
	- Sequence modification.
	- Timing modification (delete or repeat messages).
- Message authentication is concerned with:
	- Protecting the integrity of a message.
	- Validating the identity of the originator of the message.
	- Validating sequencing & timeliness.
	- Non-repudiation of origin (dispute resolution).
- # Hash Functions
	- A hash function is a variation of a MAC, which produces a fixed-size hash code ("fingerprint") based on a variably-sized input message.
	- A hash function is public and is not keyed, therefore the hash value must be encrypted.
	- Traditional CRCs are too weak and cannot be used.
		- 128-512 bit hash values are regarded as suitable.
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