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Re: [TLS] Clarifications and questions: TLS1.3 - Static RSA and AEAD

"Blumenthal, Uri - 0558 - MITLL" <uri@ll.mit.edu> Tue, 27 May 2014 18:01 UTC

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From: "Blumenthal, Uri - 0558 - MITLL" <uri@ll.mit.edu>
To: Michael StJohns <msj@nthpermutation.com>, "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] Clarifications and questions: TLS1.3 - Static RSA and AEAD
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Date: Tue, 27 May 2014 18:01:31 +0000
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Subject: Re: [TLS] Clarifications and questions: TLS1.3 - Static RSA and AEAD
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On 5/27/14 13:49 , "Michael StJohns" <msj@nthpermutation.com> wrote:

>On 5/27/2014 9:59 AM, Blumenthal, Uri - 0558 - MITLL wrote:
>> IVs:  contrary to what some people tend to believe, IV does not have to
>>be
>> random (or even unpredictable). Being unique is sufficient in many
>>cases,
>> including AEAD.
>
>Hi Uri -
>
>I seem to remember for some modes that the IV has to unpredictable - I
>believe that CBC was one. (But may be mitigated by integrity checks to
>defeat chosen plain text attacks?

Yes and yes. AFAIR. Which is why I'm not a fan of CBC (in addition to
having to worry about padding :).

>I don't have time to search for a
>cite).  You are correct that uniqueness is the only requirement for
>AEAD, but mostly AEAD IVs are constructed from a [random nonce][per
>message value][block counter 0] concatenation - the random nonce
>enforces the uniqueness.

Random nonce = per-key-change. Per-message value could be also a counter.

;)

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