Re: [TLS] Two draft-22 comments

Eric Rescorla <ekr@rtfm.com> Fri, 08 December 2017 19:14 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 8 Dec 2017 11:13:56 -0800
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To: Joseph Birr-Pixton <jpixton@gmail.com>
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Subject: Re: [TLS] Two draft-22 comments
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On Fri, Dec 8, 2017 at 10:49 AM, Joseph Birr-Pixton <jpixton@gmail.com>;
wrote:

> Hello,
>
> Draft 22 says:
>
>   An implementation may receive an unencrypted record of type
>   change_cipher_spec consisting of the single byte value 0x01 at any
>   time during the handshake and MUST simply drop it without further
>   processing.
>
> That requirement is hard to meet in a library that implements both
> TLS1.2 and TLS1.3 -- a CCS prior to ServerHello would have to be both
> fatally rejected (TLS1.2) and dropped without further processing
> (TLS1.3).
>

Well, you could read this as overriding the 1.2 requirement, namely, that if
you offer 1.3, you must reject it.


> Are there any problems with tightening up "at any time during the
> handshake"? Or perhaps I should be interpreting the time prior to
> ServerHello as not being "during the handshake"?
>

I think if we think this is the right answer we should say so, and I would
be
fine with that.


There's inconsistency in whether the supported_versions extension is
> allowed in HelloRetryRequest.  4.2.1 and B.3.1.1 say no, but 4.1.4,
> 4.2 and 9.2 say yes. I'll assume that's an omission and submit a PR.
>

Correct. Please do.

-Ekr


>
> Cheers,
> Joe
>
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