Unformatted text preview: lleged sender –
Include a sequence number, assured proper sequence – no
replay CBC-residue as MAC CBC-residue, aka DAC = Data Authentication Code CBC-residue as MAC (cont’d) 1. 2. The last encrypted block, aka the CBC residue, can be used as a
“Message Authentication Code” (MAC) for a message as follows:
The sender transmits the original message in plaintext together with the
the CBC residue (but NOT the key, of course)
The receiver, who knows the key in advance, can then encrypt the
plaintext upon its arrival using CBC mode. If the message has been
tampered with during transmission, the CBC residue won’t match !
Notice in this case, CBC is used for MAC purpose and does NOT provide
secrecy at all ;
If both secrecy and message-authenticity (tamper-proof) is required, we
need to do CBC twice in 2 passes with 2 different keys: 1st pass for encryption, 2nd pass to generate the CBC-residue for...
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- Fall '13
- hash function, Cryptographic hash function, message digest, one-way hash function