Re: deprecating MD5 in signature verification for gnutls-{cli, serv}

[Daniel Kahn Gillmor]

On 01/05/2009 02:31 PM, Daniel Kahn Gillmor wrote:
>  I'm sorry that i haven't had the time to debug this further yet.

Ok, i got to look into it tonight with gdb against the gnutls 2.6.3
libraries (i'm using the versions from debian experimental).  here's
what i found:

gnutls_certificate_verify_peers2() ultimately calls
_gnutls_verify_certificate2(), which (at lib/x509/verify.c:321) properly
sets the flags in the output variable, but does not set ret to 0.

gnutls_x509_crt_list_verify(), the immediate caller of
_gnutls_verify_certificate2(), does not check the data in *output unless
the return code is actually zero.

So i suspect that the following is the correct patch (against the git
head), but i have not tested it yet (and i need to sleep before it gets
any later):

diff --git a/lib/x509/verify.c b/lib/x509/verify.c
index 02964ba..c00b4bf 100644
--- a/lib/x509/verify.c
+++ b/lib/x509/verify.c
@@ -320,6 +320,7 @@ _gnutls_verify_certificate2 (gnutls_x509_crt_t cert,
        {
          if (output)
            *output |= GNUTLS_CERT_INSECURE_ALGORITHM | GNUTLS_CERT_INVALID;
+         ret = 0;
        }
     }

@@ -1036,6 +1037,7 @@ _gnutls_verify_crl2 (gnutls_x509_crl_t crl,
       {
        if (output)
          *output |= GNUTLS_CERT_INSECURE_ALGORITHM | GNUTLS_CERT_INVALID;
+       ret = 0;
       }
   }

Any thoughts about this proposal?  This would affect the built-in X.509
verification routines, not just gnutls-cli and gnutls-serv.

        --dkg

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