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Re: [Acme] Fixing the TLS-SNI challenge type

Jonathan Rudenberg <jonathan@titanous.com> Fri, 12 January 2018 03:30 UTC

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From: Jonathan Rudenberg <jonathan@titanous.com>
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Date: Thu, 11 Jan 2018 22:29:58 -0500
Cc: Roland Bracewell Shoemaker <roland@letsencrypt.org>, IETF ACME <acme@ietf.org>
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To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [Acme] Fixing the TLS-SNI challenge type
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> On Jan 11, 2018, at 22:26, Martin Thomson <martin.thomson@gmail.com> wrote:
> 
> If you are using a new protocol, all of the concerns Peter have come
> into play.  If you are there, why wouldn't you do the challenge
> validation within the new protocol rather than using the certificate
> (which is sent in the clear in current TLS versions).  That might be
> easier to implement than generating the self-signed certificate…

I don’t think an entirely new protocol makes sense. In order to do the TLS/SNI/ALPN handshake a certificate is already sent in the ServerHello, so there’s no reason not to use it to transport the authorization token. Generating a self-signed certificate is trivial, and I’m not aware of any relevant security concerns around fetching the authorization in the clear (the dns-01 and http-01 challenge types are plaintext as well).

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