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Re: [TLS] WGLC: draft-ietf-tls-session-hash

Martin Thomson <martin.thomson@gmail.com> Thu, 15 January 2015 23:21 UTC

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Date: Thu, 15 Jan 2015 15:21:26 -0800
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From: Martin Thomson <martin.thomson@gmail.com>
To: Eric Rescorla <ekr@rtfm.com>
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Cc: Stephen Checkoway <s@pahtak.org>, "TLS@ietf.org (tls@ietf.org)" <tls@ietf.org>
Subject: Re: [TLS] WGLC: draft-ietf-tls-session-hash
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On 15 January 2015 at 14:51, Eric Rescorla <ekr@rtfm.com> wrote:
> For sessions negotiated without EMS:
> - SHOULD not resume
> - MUST not resume sessions if the client offers EMS in the resumption
>   (and therefore SHOULD do a complete negotiation).
>
> For sessions negotiated with EMS:
> - The client ??? offer EMS
> - The server MUST NOT echo it?

Just to be clear, this latter part is...when renegotiating.

My preference is: if the session had EMS, when renegotiating:
 - the client MUST offer the extension, and
 - the server MUST fail the handshake (new alert needed?) if the
extension isn't present.

That means no resumption, OR fallback to the complete handshake.

I think that I'd prefer to have the server echo the extension in this
case too.  It's a few bytes effectively wasted, but it makes
everything nice and symmetrical.  Clients says "I want EMS" and server
says "you got EMS".

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