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Re: [saag] SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1

Alan DeKok <aland@deployingradius.com> Wed, 08 January 2020 03:22 UTC

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From: Alan DeKok <aland@deployingradius.com>
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Date: Tue, 07 Jan 2020 22:22:12 -0500
Cc: Phillip Hallam-Baker <phill@hallambaker.com>, IETF SAAG <saag@ietf.org>
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To: Andrey Jivsov <crypto@brainhub.org>
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Subject: Re: [saag] SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1
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> On Jan 7, 2020, at 10:18 PM, Andrey Jivsov <crypto@brainhub.org> wrote:
> 
> Even more precise, the hash algorithm in X.509 certificate trust anchors doesn't matter for security. Self-signed X.509 certs are the most common trust anchors. 
> 
> If a self-signed cert is a part of a certificate chain, it must be a trust anchor. Therefore, the hash algorithm in a self-signed X.509 certificate never matters for security. This should include compliance reasons of "no SHA-1" because the signature field on self-signed cert should never be verified (we can, but it just wastes compute cycles).
> 
> Remarkably, the above straightforward facts are for some reason not well-understood and companies make an effort to remove X.509 trust anchors with SHA-1 in signatures over them.

  My $0.02 is it's because it's easier to say "get rid of SHA1" than to explain to people where / when it can be used, and why.  I'm not sure that they're wrong.

  Alan DeKok.

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