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Re: Size of IV field in DES-CBC mode
At 1:33pm 12/19/94 -0500, uri@watson.ibm.com wrote:
>Phil Karn says:
>> Do we really need a full 8 bytes for the IV field in the baseline
>> DES-CBC mode? 4 bytes would be enough to maintain 32-bit alignment of
>> the next-layer transport header (e.g., TCP, UDP or IP). And if these 4
>> bytes are mapped properly into the actual 8-byte DES IV field they
>> should do an acceptable job of ensuring that every packet ciphertext
>> is completely different even when the corresponding plaintext begins
>> with constant values (e.g., TCP or UDP port numbers).
What this means is that the number of packets until there are 2 with the
same IV is 65K packets. 2 packets with the same IV is not necessarily a
problem.
Jim
----------------------
James P Hughes <hughes@hughes.network.com>
Key fingerprint = 68 E7 D5 75 3C 88 86 71 D4 34 36 C3 8E DD 48 17
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