[TLS] TLSv1.2 - Is zero signature allowed in client CertificateVerify message?

M K Saravanan <mksarav@gmail.com> Mon, 02 September 2019 03:32 UTC

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From: M K Saravanan <mksarav@gmail.com>
Date: Mon, 2 Sep 2019 11:32:11 +0800
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Subject: [TLS] TLSv1.2 - Is zero signature allowed in client CertificateVerify message?
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Hi,

Is zero signature allowed in client CertificateVerify message (I am
guessing may be to indicate error condition??). I don't see any thing
related to zero signature in the TLS 1.2 RFC (or may be I am not looking
into the right section?)

Today I saw a packet like this and server was terminating the connection
due to the failure of client cert auth. (because of zero signature in
client cert verify message).

[image: image.png]

Under what circumstances a client can send a zero signature in the client
CertificateVerify message?  Is this behaviour TLS 1.2 RFC compliant?

with regards,
Saravanan