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Re: [TLS] Resolution AEAD Cipher length and padding

"Joseph Salowey (jsalowey)" <jsalowey@cisco.com> Mon, 21 July 2014 15:11 UTC

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From: "Joseph Salowey (jsalowey)" <jsalowey@cisco.com>
To: Alfredo Pironti <alfredo@pironti.eu>
Thread-Topic: [TLS] Resolution AEAD Cipher length and padding
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Date: Mon, 21 Jul 2014 15:10:58 +0000
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Subject: Re: [TLS] Resolution AEAD Cipher length and padding
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On Jul 21, 2014, at 7:54 AM, Alfredo Pironti <alfredo@pironti.eu<mailto:alfredo@pironti.eu>> wrote:

It's not clear to me what this resolution is about; could you please elaborate (or give pointers)?
Is this about AEAD ciphers built on top of block-encrypt then mac? To some extent, current GCM and CCM ciphers are already expanding the cipher text length by the tag length, so I must be missing the point here. Thanks.


[Joe] to clarify:  current AEAD cipher modes (GCM, CCM)  do not expand the cipher text through padding, their cipher text length is the same as the clear text length.  With the current construction you cannot support an AEAD mode build out of an AES-CBC cipher because the cipher text length would not be the same as the clear text length.  This resolution would change the construction to support AEAD ciphers that perform padding.


Best,
Alfredo


On Mon, Jul 21, 2014 at 4:41 PM, Joseph Salowey (jsalowey) <jsalowey@cisco.com<mailto:jsalowey@cisco.com>> wrote:
At the interim meeting we decided to fix the specification of AEAD to support ciphers that pad and expand the cipher text length.  Please respond to this message by Friday, July 25 if you have an objection.

Thanks,

Joe
[for the chairs]
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