Re: [TLS] Consensus Call: FNV vs SHA1

Nicolas Williams <> Mon, 10 May 2010 19:25 UTC

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Date: Mon, 10 May 2010 14:09:55 -0500
From: Nicolas Williams <>
To: "Joseph Salowey (jsalowey)" <>
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Subject: Re: [TLS] Consensus Call: FNV vs SHA1
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On Mon, May 10, 2010 at 10:39:28AM -0700, Joseph Salowey (jsalowey) wrote:
> I don't see much new being added to this discussion at this point.  I'd
> like to close on this.  If you have an opinion please indicate if:
> a) You favor SHA-1
> b) You favor FNV-1a

I lean towards (a) from a purely political point of view: I don't think
it's a good idea to train auditors to act reflexively.  However, from a
purely technical point of view I have no preference whatsoever at this
time, but I'd like answers to my questions below.

If the consensus is (b) then I think the following changes should be

 - Add an informative reference to FNV (and expand the acronym).

 - Refer to FNV as a checksum (or even hash, or better, non-
   cryptographic hash) rather than as a digest.

   In the context of TLS )RFC5246), "digest" definitely refers to
   cryptographic hash functions.  We should not confuse the terminology.

 - Add a description of what happens if cached object checksums collide.

   No, the current security considerations section doesn't deal with
   this, and rightly so _if_ collisions are not a security problem, but
   what happens when there are collisions?  Do hanshakes fail?

   Also, could caching have been done without reference to hash
   functions?  E.g., by having servers assign IDs to objects for client
   caching?  Is it too late to consider this approach?