Subject: [ietf-tls] Re: Re: London

From: Bodo Moeller <[email-masked]>
Date: Mon, 16 Jul 2001 16:27:34 +0200

On Mon, Jul 16, 2001 at 07:16:42AM -0700, Eric Rescorla wrote:
> Bodo Moeller <[email-masked]> writes:

>> Last I checked (Windows 2000 Professional, IE 5.50.whatever), IE still
>> had SSL 2.0 support enabled by default, so it used the SSL 2.0
>> CLIENT-HELLO format.  If you disabled SSL 2.0 and enabled TLS 1.0 (the
>> latter was disabled by default), it did not use the SSL 3.0
>> ClientHello format as it should have done, but the TLS 1.0 ClientHello
>> format; that is, the record header contained a 'version' value of
>> {0x03, 0x01}, i.e. the 'client_version' value, while it should contain
>> {0x03, 0x00} for backwards compatibility.

> This sounds like the correct behavior to me.

Which one?  RFC 2246 appendix E says that the SSL 3.0 record format
should be used for connection attempts if SSL 3.0 backwards
compatibility is desired.  Thus 'version' in the record headers ('The
version of the protocol being employed') should be {0x03, 0x00}, while
'client_version' in the actual ClientHello message ('The version of
the TLS protocol by which the client wishes to communicate during this
session') must be {0x03, 0x01}.  Of course, as long as ClientHello
formats stay consistent, servers can simply ignore the minor digit of
the record header 'version' field.

>> With ClientHellos built like this, IE avoided the bug in servers that
>> use 'version' where they should use 'client_version' -- in those
>> ClientHellos, these two were the same value, after all.

> As I understood it, the client_version/version problem was about
> checking in the PMS decryption process. Is there any server which
> is confused about version checking in the record layer?

I'm not sure I understand this question.  If a server uses 'version'
instead of 'client_version' for premaster secret decryption
verification and the values odiffer, then the handshake quite simply
will fail.

-- 
Bodo Möller <[email-masked]>
PGP http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller/0x36d2c658.html
* TU Darmstadt, Theoretische Informatik, Alexanderstr. 10, D-64283 Darmstadt
* Tel. +49-6151-16-6628, Fax +49-6151-16-6036

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