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Re: [TLS] Deprecating SSLv3

Ronald del Rosario <rrosario@five9.com> Fri, 21 November 2014 16:22 UTC

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From: Ronald del Rosario <rrosario@five9.com>
To: Nikos Mavrogiannopoulos <nmav@redhat.com>, Alfredo Pironti <alfredo@pironti.eu>
Thread-Topic: [TLS] Deprecating SSLv3
Thread-Index: AQHQAco2e4qtTz+EvUazdX0Ck5kotZxkWiWAgAdsKID//4SnAA==
Date: Fri, 21 Nov 2014 16:22:01 +0000
Message-ID: <D094A690.18053%rrosario@five9.com>
References: <CABkgnnWw9zsrqQzHVU0vXLJM+HBK3QYxJAZE+0kgGkEQEzwS=w@mail.gmail.com> <5462714E.5020201@polarssl.org> <CABkgnnUm=6TriH9UU-Uv8_rWt_CEvW1Xy8P_955ryFCvn3mWOA@mail.gmail.com> <1193984696.9333579.1416162106243.JavaMail.zimbra@redhat.com> <CALR0uiLfH-p9EbGF_=J8XMEuMczMsZJMfECKDt5E0Q9BBEpDOQ@mail.gmail.com> <1416584605.18312.21.camel@dhcp-2-127.brq.redhat.com>
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Cc: "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Deprecating SSLv3
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3. The document doesn't provide any instructions for clients that have
no other way to communicate with a server that only supports SSL 3.0.
MUST NOT is nice in theory, but can only be enforced on the systems one
has control on, and if the advise is followed to the letter legacy
systems (not talking of web) will be only be accessible in plaintext.
I'd expect prohibiting the fallback dance instead, and requiring that
SSL 3.0 is negotiated only if TLS 1.0 or later are advertised in the
clientHello.

+1

Ron F. del Rosario
Information Security Officer

[cid:C1FFC277-777B-42EE-B330-35D87AA7FD50]

Five9, Inc.
Cloud Contact Center Software

From: Nikos Mavrogiannopoulos <nmav@redhat.com<mailto:nmav@redhat.com>>
Date: Friday, November 21, 2014 at 7:43 AM
To: Alfredo Pironti <alfredo@pironti.eu<mailto:alfredo@pironti.eu>>
Cc: "tls@ietf.org<mailto:tls@ietf.org>" <tls@ietf.org<mailto:tls@ietf.org>>
Subject: Re: [TLS] Deprecating SSLv3

On Sun, 2014-11-16 at 23:22 +0100, Alfredo Pironti wrote:


Yes, I agree this is a fair point. I'll complete the wording tomorrow
in the pending PR, and these ideas will get into the updated version.

Some additional comments:
1. It has quite awkward structure. The main body of the document is at
the introduction section.

2. The text "Negotiation of SSLv3 from any version of TLS MUST NOT be
permitted."
Not sure I understand what it means. Does it mean that fallback to SSL
3.0 from any version of TLS MUST NOT be permitted?

3. The document doesn't provide any instructions for clients that have
no other way to communicate with a server that only supports SSL 3.0.
MUST NOT is nice in theory, but can only be enforced on the systems one
has control on, and if the advise is followed to the letter legacy
systems (not talking of web) will be only be accessible in plaintext.
I'd expect prohibiting the fallback dance instead, and requiring that
SSL 3.0 is negotiated only if TLS 1.0 or later are advertised in the
clientHello.

regards,
Nikos



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