[Cfrg] Fwd: Mail regarding draft-irtf-cfrg-chacha20-poly1305

Yoav Nir <ynir.ietf@gmail.com> Fri, 17 October 2014 16:25 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Fri, 17 Oct 2014 19:25:43 +0300
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Subject: [Cfrg] Fwd: Mail regarding draft-irtf-cfrg-chacha20-poly1305
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Message from David Black:

> This nonce reuse warning in Section 4 somewhat on the light side:
>   Consequences of repeating a nonce: If a nonce is repeated, then both
>   the one-time Poly1305 key and the key-stream are identical between
>   the messages.  This reveals the XOR of the plaintexts, because the
>   XOR of the plaintexts is equal to the XOR of the ciphertexts.
> Here's some blunter text that could be used as a model - this was driven
> into RFC 7146 by the secdir reviewer (it applies to all stream ciphers
> and all modes that behave like stream ciphers):
>   Of particular interest are the security considerations concerning the
>   use of AES GCM [RFC4106] and AES GMAC [RFC4543]; both modes are
>   vulnerable to catastrophic forgery attacks if a nonce is ever
>   repeated with a given key.
> Thanks,
> --David
> ----------------------------------------------------
> David L. Black, Distinguished Engineer
> EMC Corporation, 176 South St., Hopkinton, MA  01748
> +1 (508) 293-7953             FAX: +1 (508) 293-7786
> david.black@emc.com        Mobile: +1 (978) 394-7754
> ----------------------------------------------------