While we are running test for client cert auth between the new IE version that
supports TLS 1.1/1.2 and our server (running openssl 0.9.8d, only supports up
to TLS1.0) which initiates server renegotiation for the client cert, we noticed
that the IE sends the wrong version number in the PreMasterSecret in the
renegotiation cycle. Then the server generates an alert and fails the
handshaking.
However according to the RFC, it says the server should randomize the
PreMasterSecret in case of error, rather than generate an alert. See below from
the RFC:
Note: The version number in the PreMasterSecret MUST be the version
offered by the client in the ClientHello, not the version
negotiated for the connection. This feature is designed to
prevent rollback attacks. Unfortunately, many implementations
use the negotiated version instead, and therefore checking the
version number may lead to failure to interoperate with such
incorrect client implementations. Client implementations, MUST
and Server implementations MAY, check the version number. In
practice, since the TLS handshake MACs prevent downgrade and no
good attacks are known on those MACs, ambiguity is not
considered a serious security risk. Note that if servers
choose to check the version number, they should randomize the
PreMasterSecret in case of error, rather than generate an
alert, in order to avoid variants on the Bleichenbacher attack.
[KPR03]
7.4.7.1. RSA Encrypted Premaster Secret Message
Does openSSL have a fix in that behavior in newer versions?
Thanks,
-binlu
-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Dr. Stephen Henson
Sent: Thursday, March 01, 2012 5:26 AM
To: [email protected]
Subject: Re: OpenSSL & "Security Update for Windows Server 2008 R2 x 64 Edition
(KB2585542)"
Since I can't reproduce this I'm wondering if the CAC cards introduce an
additional element. I can see two possible reasons why they might:
1. Client authentication requires renegotiation if it is enabled on certain
webpages and not across the whole site. The was a problem with version numbers
in premaster secrets with IIS which has been fixed: I wonder if there is a
similar one with MSIE which affects OpenSSL servers.
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