Possible crypto backdoor in RFC-2631 Diffie-Hellman Key Agreement Method

[Georgi Guninski]

On Sat, Sep 05, 2015 at 03:40:24PM +0000, Alfonso De Gregorio wrote:
> On Sat, Sep 5, 2015 at 3:25 PM, Georgi Guninski <guninski at guninski.com> wrote:
> ...
> > I mean: non-proper DH is implementation which doesn't return
> > error/aborts if $q$ is composite. $q$ is defined in the RFC.
> 
> I'm not aware of any implementation that fails to abort is q is composite.
> 
> As a case in point, OpenSSL versions implementing X9.42 DH
> (1.0.2-Beta2 and above) test both p and q for primality:
> 
> int DH_check(const DH *dh, int *ret)
> {
>    /* ... */
> 
>     if (dh->q) {
>         /* ... */
>         if (!BN_is_prime_ex(dh->q, BN_prime_checks, ctx, NULL))
>             *ret |= DH_CHECK_Q_NOT_PRIME;


In 1.0.1p is_prime() is such a mess, it appears to often return $-1$
by quick audit.

Did you check the explicit POC in this thread against this version
of openssl?