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Re: [TLS] [Technical Errata Reported] RFC5288 (4694)

Peter Gutmann <pgut001@cs.auckland.ac.nz> Sun, 15 May 2016 08:53 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Aaron Zauner <azet@azet.org>
Thread-Topic: [TLS] [Technical Errata Reported] RFC5288 (4694)
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Date: Sun, 15 May 2016 08:52:56 +0000
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Subject: Re: [TLS] [Technical Errata Reported] RFC5288 (4694)
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Aaron Zauner <azet@azet.org> writes:

>What do you think nonce stands for?
>https://en.wikipedia.org/wiki/Cryptographic_nonce

Well there's your first mistake, you're using Wikipedia as a reference.
"nonce" is from medieval English, and predates modern cryptography and IVs by
about 800 years.

>In TLS nonce reuse allows us to attack the authentication key of GCM. Not the
>actual master secret. There's no direct break of the confidentiality, 

If you reuse the IV/nonce in GCM (or more specifically CTR mode), you repeat
the cipher stream.  An XOR makes it go away, so you lose any confidentiality.

Peter.

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