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Re: [TLS] drop obsolete SSL 2 backwards compatibility from TLS 1.3 draft

Andrei Popov <Andrei.Popov@microsoft.com> Thu, 12 February 2015 23:53 UTC

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From: Andrei Popov <Andrei.Popov@microsoft.com>
To: Yuhong Bao <yuhongbao_386@hotmail.com>, Florian Weimer <fweimer@redhat.com>, "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] drop obsolete SSL 2 backwards compatibility from TLS 1.3 draft
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Date: Thu, 12 Feb 2015 23:53:16 +0000
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Archived-At: <http://mailarchive.ietf.org/arch/msg/tls/ArXf2u9mkriuXaVafD78q3ajp_c>
Subject: Re: [TLS] drop obsolete SSL 2 backwards compatibility from TLS 1.3 draft
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I confirm.

Cheers,

Andrei

-----Original Message-----
From: Yuhong Bao [mailto:yuhongbao_386@hotmail.com] 
Sent: Thursday, February 12, 2015 3:48 PM
To: Florian Weimer; tls@ietf.org
Cc: Andrei Popov
Subject: RE: [TLS] drop obsolete SSL 2 backwards compatibility from TLS 1.3 draft

> On 12/24/2014 08:02 AM, Yuhong Bao wrote:
>>>>
>>>> There's no reason to maintain any backwards support here just for 
>>>> Internet Explorer 2.0 on Windows 3.1.
>>>>
>>>
>>> I'm not objecting to the change, but I am objecting to the hyperbole. The issue is with Internet Explorer 6 on Windows XP, which still exists, but more importantly, a lot of web service clients running on top of Windows XP use the same SCHANNEL library as IE would use, so they issue a SSLv2 ClientHello. Despite Microsoft's best efforts, there is still a substantial but diminishing install base of XP.
>>>
>>> It's fine for us to break compatibility with these clients, but let's not pretend it's some ancient technology that doesn't exist in the market anymore.
>>>
>> If needed, one suggestion would be to cap the old SSLv2 ClientHello to TLS 1.2.
>
> At least make it TLS 1.1 instead. With TLS 1.2, the SSLv2 ClientHello 
> cannot include the signature algorithms extension, so SHA-1 is used 
> instead of the concatenation of MD5 and SHA-1, and this usually not 
> what is wanted.

Just confirmed that IE on Win7 even when misconfigured to enable SSLv2 doesn't send a SSLv2 ClientHello with TLS 1.2 on it which means that SChannel probably can't do it at all. Andrei Popov should be able to confirm this.

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