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Re: [TLS] The TLS_FALLBACK_SCSV time bomb (was: Re: Working Group Last Call for draft-ietf-tls-downgrade-scsv-00)

Andrei Popov <Andrei.Popov@microsoft.com> Mon, 20 October 2014 22:36 UTC

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From: Andrei Popov <Andrei.Popov@microsoft.com>
To: Yuhong Bao <yuhongbao_386@hotmail.com>, "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] The TLS_FALLBACK_SCSV time bomb (was: Re: Working Group Last Call for draft-ietf-tls-downgrade-scsv-00)
Thread-Index: AQHP6g/vkqpMmvBKoUCxL3G2jHnzlpw0TqsAgABoBICAAAgfwIABAiWAgAB5PrWAA1xREA==
Date: Mon, 20 Oct 2014 22:36:28 +0000
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References: <2112FCAD-4820-49D9-9871-6501C83A554D@cisco.com> <543F9893.806@redhat.com> <543FA0A0.1030205@polarssl.org> <543FCAED.50502@redhat.com> <2A0EFB9C05D0164E98F19BB0AF3708C71D39ECECB4@USMBX1.msg.corp.akamai.com> <5440E005.6000607@redhat.com> <180027849.13041583.1413544466157.JavaMail.zimbra@redhat.com> <CADMpkcL2mntDd0dOruziqF0F=xURnqGgd_YkpF+ONzz8v-wQ9Q@mail.gmail.com> <1354095824.13104897.1413553221955.JavaMail.zimbra@redhat.com> <CADMpkcLRCsfQSr0=f97kXJw3RwHN5A79MYQ2j7XaxPxUy2MCLg@mail.gmail.com> <CABkgnnUBYtWUY-CZDDzFiDpMWYbca74o6kejh2Q3L+FHVaHoOA@mail.gmail.com> <d8ce6c7437404bcbbea3a17e5c0b1582@BL2PR03MB419.namprd03.prod.outlook.com> <CADMpkcK4wCkLMU_Ga2fX3CWxXyU+D1Qgg1s77ttVq6LTo50XxA@mail.gmail.com> <loom.20141018T210052-775@post.gmane.org>
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Archived-At: http://mailarchive.ietf.org/arch/msg/tls/swPaPRVz9r3-BoVwjV3pjA6bCHY
Subject: Re: [TLS] The TLS_FALLBACK_SCSV time bomb (was: Re: Working Group Last Call for draft-ietf-tls-downgrade-scsv-00)
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It would be nice to keep TLS extensions optional; unfortunately, TLS extensions mechanism is already used to patch protocol security issues: renegotiation info, extended master secret extensions come to mind. I think we've crossed this bridge a long time ago.

Cheers,

Andrei

-----Original Message-----
From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Yuhong Bao
Sent: Saturday, October 18, 2014 12:03 PM
To: tls@ietf.org
Subject: Re: [TLS] The TLS_FALLBACK_SCSV time bomb (was: Re: Working Group Last Call for draft-ietf-tls-downgrade-scsv-00)

Bodo Moeller <bmoeller <at> acm.org> writes:
> Even once we no longer need to worry about extension *intolerant* 
> servers,
we still should take into account that extension *support* remains optional for TLS servers. Servers can legitimately ignore ClientServer.extensions entirely. Having a fallback_indication TLS extension would be overly onerous for such servers: they'd need to implement extension parsing just to be able to find this one signal. 
MS had to do this in order to backport the TLS renegotiation extension to XP/Server 2003 back in 2010.

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