Use X509_get_signature_info to get signature strength.

static int ssl_security_cert_sig(SSL *s, SSL_CTX *ctx, X509 *x, int op)

{

    /* Lookup signature algorithm digest */

    int secbits = -1, md_nid = NID_undef, sig_nid;

    int secbits, nid, pknid;

    /* Don't check signature if self signed */

    if ((X509_get_extension_flags(x) & EXFLAG_SS) != 0)

        return 1;

    sig_nid = X509_get_signature_nid(x);

    if (sig_nid && OBJ_find_sigid_algs(sig_nid, &md_nid, NULL)) {

        const EVP_MD *md;

        if (md_nid && (md = EVP_get_digestbynid(md_nid)))

            secbits = EVP_MD_size(md) * 4;

    }

    if (!X509_get_signature_info(x, &nid, &pknid, &secbits, NULL))

        secbits = -1;

    /* If digest NID not defined use signature NID */

    if (nid == NID_undef)

        nid = pknid;

    if (s)

        return ssl_security(s, op, secbits, md_nid, x);

        return ssl_security(s, op, secbits, nid, x);

    else

        return ssl_ctx_security(ctx, op, secbits, md_nid, x);

        return ssl_ctx_security(ctx, op, secbits, nid, x);

}

int ssl_security_cert(SSL *s, SSL_CTX *ctx, X509 *x, int vfy, int is_ee)