Re: [TLS] Pull Request: Removing the AEAD explicit IV

Eric Rescorla <ekr@rtfm.com> Sat, 21 March 2015 19:23 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Sat, 21 Mar 2015 12:22:44 -0700
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To: Adam Langley <agl@imperialviolet.org>
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Subject: Re: [TLS] Pull Request: Removing the AEAD explicit IV
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On Sat, Mar 21, 2015 at 12:20 PM, Adam Langley <agl@imperialviolet.org>;
wrote:

> On Sat, Mar 21, 2015 at 11:58 AM, Eric Rescorla <ekr@rtfm.com>; wrote:
> > Adam, Brian, what would you think of XOR rather than addition?
> >
> > E.g., generate a per-connection value V and then do:
> >
> > Nonce = Seq XOR V?
>
> It's invertable so can't break uniqueness. So that would be ok too. Is
> V a 12-byte (or whatever) value and thus fixes the upper 4 (or
> whatever) bytes of the nonce?
>

I was thinking that we would generate an N_MIN long V and XOR
it with Seq. So, yes, N_MAX - 8 bytes would be effectively fixed.

-Ekr