Thank David. I originally encountered the zero bytes in the signature field (the screenshot I posted in my mail) with a client device during client cert auth.
Android Version: 6.0.1 Hardware: samsung SM-T580 (Galaxy Tab A6) It was sending proper client Certificate, but it was sending client CertificateVerify with zero bytes in the signature. Hence I was wondering whether this behaviour is allowed or not as per TLS 1.2 RFC. (for e.g. when the client encountered an error condition; in such cases ideally I expect the client to terminate the connection with an alert like you suggested). Looks like a bug on the client side then. with regards, Saravanan On Tue, 3 Sep 2019 at 23:40, David Benjamin <david...@chromium.org> wrote: > The client should just abort the handshake and probably send an alert like > internal_error since it cannot usefully proceed. > > On Tue, Sep 3, 2019 at 11:27 AM M K Saravanan <mksa...@gmail.com> wrote: > >> Thanks Richard for the reply. Let me rephrase my question: >> >> If a client encounter any error condition (e.g. does not have access to >> the private key for whatever reason) in generating the signature, can it >> send zero bytes in the signature field of CertificateVerify message to >> indicate the error condition? Is this allowed in TLS 1.2 RFC? >> >> with regards, >> Saravanan >> >> >> On Tue, 3 Sep 2019 at 22:36, Richard Barnes <r...@ipv.sx> wrote: >> >>> I don't believe that's a valid signature according to rsa_pkcs1_sha256, >>> so yeah, this is probably an error. >>> --Richard >>> >>> On Sun, Sep 1, 2019 at 11:33 PM M K Saravanan <mksa...@gmail.com> wrote: >>> >>>> 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 >>>> >>>> >>>> >>>> _______________________________________________ >>>> TLS mailing list >>>> TLS@ietf.org >>>> https://www.ietf.org/mailman/listinfo/tls >>>> >>> _______________________________________________ >> TLS mailing list >> TLS@ietf.org >> https://www.ietf.org/mailman/listinfo/tls >> >
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