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Re: [TLS] HKDF

Yoav Nir <ynir.ietf@gmail.com> Tue, 24 March 2015 04:58 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Mon, 23 Mar 2015 23:58:08 -0500
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To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [TLS] HKDF
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> On Mar 23, 2015, at 9:19 AM, Eric Rescorla <ekr@rtfm.com> wrote:
> 
> As I mentioned in a previous message [0] during the interim we discussed
> moving from the TLS PRF to HKDF [RFC5869].
> 
> The general sentiment was:
> 
> - Move to HKDF
> - Specify both SHA-256 and SHA-384 (the latter being required for
>   Suite B)
> 
> This is also the time when we would want to look at adjusting
> the key expansion to separate keys and IVs (assuming we still
> have IVs).
> 
> Please use this thread to discuss this topic.
> 

OK, since you’re proposing to abandon the current TLS PRF:

1. Why? What is wrong with the TLS PRF, and 
2. If we’re changing it, why not to a fast PRF such as blake2?

Yoav

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