Re: [TLS] Expanded alert codes

Peter Gutmann <> Tue, 22 May 2018 02:17 UTC

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From: Peter Gutmann <>
To: Ion Larranaga Azcue <>, Eric Rescorla <>
CC: "Dale R. Worley" <>, "<>" <>
Thread-Topic: Expanded alert codes
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Date: Tue, 22 May 2018 02:16:53 +0000
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Subject: Re: [TLS] Expanded alert codes
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Ion Larranaga Azcue <> writes:

>I would say it's unfair to expect other people to diagnose the problem by
>claiming "that information was all that was available" because you had access
>- traffic dumps of the failing handshakes

There was no access to this.

>- traffic dumps of working handshakes

There was no access to this.

>- the possibility to try any number of modifications of the client hello to
>go from a working handshake to a failing handshake in order to identify the
>offending option or parameter

That was only after the second day of negotiations, when I managed to get
indirect access to the server to use it as an oracle, resulting in trial-and-
error modification of the client hello until the server didn't report a
handshake failure any more.

>- as you are going to have to ask the server side to activate extended
>alerts, you can ask them for server logs, as well as traffic dumps of (at
>least) the failed connections on their side (if they receive any, which is
>additional information)

Neither of those were available, and neither of them could be made available.
As I said in my previous message, the only information I had was "Handshake

>Besides, I also think it's not fair to claim that when someone disagrees, you
>are being "shouted down". 

What I meant was that as it's a non-zero amount of effort to write up a draft,
I wasn't terribly keen on putting in the effort only to have it bikeshedded to
death with "it's a security problem" (it isn't, unless you go out of your way
to make it one), "you can look at the server logs" (no, you can't), etc.  So
what I was trying to get is an idea of whether it's worth writing a draft or

>That being said... I encourage you to write your draft and look for consensus
>within the group.

OK, I'll give it a go.