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Alleged sender receiver from no masquerading no

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Unformatted text preview: lleged sender – Receiver from no masquerading no Include a sequence number, assured proper sequence – no Include proper replay 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 The “Message Authentication Code” (MAC) for a message as follows: “Message The sender transmits the original message in plaintext together with the The the CBC residue (but NOT the key, of course) the The receiver, who knows the key in advance, can then encrypt the The plaintext upon its arrival using CBC mode. If the message has been tampered with during transmission, the CBC residue won’t match ! tampered Notice in this case, CBC is used for MAC purpose and does NOT provide Notice secrecy at all ; If both secrecy and message-authenticity (tamper-proof) is required, we If 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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