[Help-gnutls] Re: Certificate verification failed

Nikos Mavrogiannopoulos nmav at gnutls.org
Thu Oct 27 11:29:44 CEST 2005

On Thursday 27 October 2005 10:56, Simon Josefsson wrote:

> > This cannot be solved. This certificate uses MD2 which is not included in
> > libgcrypt as yet. I don't know if there are plans to include it in the
> > future though.
> We could add a MD2 implementation to gnulib, to make GnuTLS support
> this when MD2 is not available through libgcrypt.  I'm working on this
> now.
That would be nice to have. 

> However, I am skeptical about supporting MD2, and even MD5, by
> default.  I know GnuTLS certtool print a warning about MD5, but the
> library does not, and most GnuTLS library users probably doesn't
> either.
Hmmm... about MD5 we are going to get a bunch of complaints if it is not 
enabled by default. But that would be the right way to do given that is not 
that hard to generate colliding certificates:

> I think we should disable both MD2 and MD5, and introduce an API to
> modify gnutls_certificate_verify_peers2, a'la
>   gnutls_enable_insecure_algorithm (&session, GNUTLS_SIGN_RSA_MD2)
This will not be necessary if we introduce the flags below. verify_peers2  
will use the flags from gnutls_certificate_set_verify_flags().

> and a new gnutls_certificate_verify_flags enumeration type, for
> gnutls_x509_crt_verify calls, e.g.:
Yes it is indeed a very nice idea. Security must be an issue in the library.

> Cheers,
> Simon

Nikos Mavrogiannopoulos

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