static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
                         DSA_SIG *sig, DSA *dsa)
{
    BN_CTX *ctx;
    BIGNUM u1, u2, t1;
    BN_MONT_CTX *mont = NULL;
    int ret = -1, i;
    if (!dsa->p || !dsa->q || !dsa->g) {
        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
        return -1;
    }

    i = BN_num_bits(dsa->q);
    /* fips 186-3 allows only different sizes for q */
    if (i != 160 && i != 224 && i != 256) {
        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
        return -1;
    }

    if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
        return -1;
    }
    BN_init(&u1);
    BN_init(&u2);
    BN_init(&t1);

    if ((ctx = BN_CTX_new()) == NULL)
        goto err;

    if (BN_is_zero(sig->r) || BN_is_negative(sig->r) ||
        BN_ucmp(sig->r, dsa->q) >= 0) {
        ret = 0;
        goto err;
    }
    if (BN_is_zero(sig->s) || BN_is_negative(sig->s) ||
        BN_ucmp(sig->s, dsa->q) >= 0) {
        ret = 0;
        goto err;
    }

    /*
     * Calculate W = inv(S) mod Q save W in u2
     */
    if ((BN_mod_inverse(&u2, sig->s, dsa->q, ctx)) == NULL)
        goto err;

    /* save M in u1 */
    if (dgst_len > (i >> 3))
        /*
         * if the digest length is greater than the size of q use the
         * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
         * 4.2
         */
        dgst_len = (i >> 3);
    if (BN_bin2bn(dgst, dgst_len, &u1) == NULL)
        goto err;

    /* u1 = M * w mod q */
    if (!BN_mod_mul(&u1, &u1, &u2, dsa->q, ctx))
        goto err;

    /* u2 = r * w mod q */
    if (!BN_mod_mul(&u2, sig->r, &u2, dsa->q, ctx))
        goto err;

    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
        mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
                                      CRYPTO_LOCK_DSA, dsa->p, ctx);
        if (!mont)
            goto err;
    }

    DSA_MOD_EXP(goto err, dsa, &t1, dsa->g, &u1, dsa->pub_key, &u2, dsa->p,
                ctx, mont);
    /* BN_copy(&u1,&t1); */
    /* let u1 = u1 mod q */
    if (!BN_mod(&u1, &t1, dsa->q, ctx))
        goto err;

    /*
     * V is now in u1.  If the signature is correct, it will be equal to R.
     */
    ret = (BN_ucmp(&u1, sig->r) == 0);

 err:
    if (ret < 0)
        DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
    if (ctx != NULL)
        BN_CTX_free(ctx);
    BN_free(&u1);
    BN_free(&u2);
    BN_free(&t1);
    return (ret);
}

This classification refers to vulnerabilities resulting from poor cryptographic key management, including weak generation, insecure storage, or improper handling that compromises encryption strength.