1. Cryptographic Hash Functions Message Authentication Digital Signatures

2. Abstract We will discuss Cryptographic hash functions Message authentication codes –HMAC and CBC-MAC Digital signatures 2

3. Encryption/Decryption Provides message confidentiality. Does it provide message authentication? 3

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8. 8 Collision-resistant hash functions can be built from collision-resistant compression functions using Merkle-Damgard construction.

10. Merkle-Damgard Construction m 1 m 2 m 3 m k f f f IV v 0 v 1 v 2 v k … f h(m)

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18. m = m 1 m 2 m 3 m s f f f IV … f h(m) k Xk X X h k (m) f h k (m) h k (m||m s+1 ) m s+1

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21. Cipher Block Chaining (CBC) 21

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23. Message m MAC k (m) Message m Sig pr (m)

25. MCED PU Bob PR Bob Alice Bob M M SED PU Bob PR Bob Alice Bob Verify Sign Encryption (using RSA): Digital signature (using RSA -1 ): E(S) =M?