Security implications of (not using) GNUTLS_VERIFY_DO_NOT_ALLOW_SAME

[Lars Noschinski]

* Simon Josefsson <simon at josefsson.org> [10-06-21 11:32]:
> > I am wondering when the flag GNUTLS_VERIFY_DO_NOT_ALLOW_SAME should be
> > used. I've seen it in use in the Wocky library[0], which is used by the
> > instant messenger client empathy.
[...]
> I don't see any normal situation where this flag is useful.
> 
> I'm not sure the behaviour you see is actually intended, I don't see why
> it should reject the chain here.  So it may be a bug...
> 
> The flag _may_ be useful if you have a X.509 Version 1 certificate as a
> trust anchor.  You may want to trust a X.509v1 CA for verifying server
> certificates signed by the X.509v1 CA, but you definitely do not want to
> accept that certificate as the server certificate (because there are no
> name restriction extensions).  On the other hand, you shouldn't use
> X.509v1 certificates anyway...

Just to clarify: Using GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT without
GNUTLS_VERIFY_DO_NOT_ALLOW_SAME is a sane choice (if one stills needs to
deal with X.509v1 certificates).

  -- Lars