Re: [Cfrg] hpke which HKDF to use for eae_prk?

Christopher Wood <caw@heapingbits.net> Thu, 20 August 2020 18:44 UTC

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Date: Thu, 20 Aug 2020 11:43:49 -0700
From: "Christopher Wood" <caw@heapingbits.net>
To: cfrg@irtf.org
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Subject: Re: [Cfrg] hpke which HKDF to use for eae_prk?
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On Thu, Aug 20, 2020, at 11:42 AM, Richard Barnes wrote:
> I think the spec is right here.  The DHKEM instances are defined with a 
> curve and a KEM, so assuming your descriptor 
> "x25519,hkdf-sha512,aesgcm128" is meant to be "KEM,KDF,AEAD", it's 
> either incomplete or it represents a DHKEM instance that isn't defined 
> in the document.  In the schemes in the document, the KDF in DHKEM is 
> matched to the size of the curve, so x25519 goes with SHA-256.  
> 
> The current test vectors wouldn't catch this misunderstanding, though, 
> so maybe it would be worth adding a case.

+1 -- we can add one such variant to the set of test vectors.

Best,
Chris