int test_builtin(BIO *out)
{
    EC_builtin_curve *curves = NULL;
    size_t crv_len = 0, n = 0;
    EC_KEY *eckey = NULL, *wrong_eckey = NULL;
    EC_GROUP *group;
    ECDSA_SIG *ecdsa_sig = NULL;
    unsigned char digest[20], wrong_digest[20];
    unsigned char *signature = NULL;
    const unsigned char *sig_ptr;
    unsigned char *sig_ptr2;
    unsigned char *raw_buf = NULL;
    unsigned int sig_len, degree, r_len, s_len, bn_len, buf_len;
    int nid, ret = 0;

    /* fill digest values with some random data */
    if (RAND_pseudo_bytes(digest, 20) <= 0 ||
        RAND_pseudo_bytes(wrong_digest, 20) <= 0) {
        BIO_printf(out, "ERROR: unable to get random data\n");
        goto builtin_err;
    }

    /*
     * create and verify a ecdsa signature with every availble curve (with )
     */
    BIO_printf(out, "\ntesting ECDSA_sign() and ECDSA_verify() "
               "with some internal curves:\n");

    /* get a list of all internal curves */
    crv_len = EC_get_builtin_curves(NULL, 0);

    curves = OPENSSL_malloc(sizeof(EC_builtin_curve) * crv_len);

    if (curves == NULL) {
        BIO_printf(out, "malloc error\n");
        goto builtin_err;
    }

    if (!EC_get_builtin_curves(curves, crv_len)) {
        BIO_printf(out, "unable to get internal curves\n");
        goto builtin_err;
    }

    /* now create and verify a signature for every curve */
    for (n = 0; n < crv_len; n++) {
        unsigned char dirt, offset;

        nid = curves[n].nid;
        if (nid == NID_ipsec4)
            continue;
        /* create new ecdsa key (== EC_KEY) */
        if ((eckey = EC_KEY_new()) == NULL)
            goto builtin_err;
        group = EC_GROUP_new_by_curve_name(nid);
        if (group == NULL)
            goto builtin_err;
        if (EC_KEY_set_group(eckey, group) == 0)
            goto builtin_err;
        EC_GROUP_free(group);
        degree = EC_GROUP_get_degree(EC_KEY_get0_group(eckey));
        if (degree < 160)
            /* drop the curve */
        {
            EC_KEY_free(eckey);
            eckey = NULL;
            continue;
        }
        BIO_printf(out, "%s: ", OBJ_nid2sn(nid));
        /* create key */
        if (!EC_KEY_generate_key(eckey)) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        /* create second key */
        if ((wrong_eckey = EC_KEY_new()) == NULL)
            goto builtin_err;
        group = EC_GROUP_new_by_curve_name(nid);
        if (group == NULL)
            goto builtin_err;
        if (EC_KEY_set_group(wrong_eckey, group) == 0)
            goto builtin_err;
        EC_GROUP_free(group);
        if (!EC_KEY_generate_key(wrong_eckey)) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }

        BIO_printf(out, ".");
        (void)BIO_flush(out);
        /* check key */
        if (!EC_KEY_check_key(eckey)) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        BIO_printf(out, ".");
        (void)BIO_flush(out);
        /* create signature */
        sig_len = ECDSA_size(eckey);
        if ((signature = OPENSSL_malloc(sig_len)) == NULL)
            goto builtin_err;
        if (!ECDSA_sign(0, digest, 20, signature, &sig_len, eckey)) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        BIO_printf(out, ".");
        (void)BIO_flush(out);
        /* verify signature */
        if (ECDSA_verify(0, digest, 20, signature, sig_len, eckey) != 1) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        BIO_printf(out, ".");
        (void)BIO_flush(out);
        /* verify signature with the wrong key */
        if (ECDSA_verify(0, digest, 20, signature, sig_len, wrong_eckey) == 1) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        BIO_printf(out, ".");
        (void)BIO_flush(out);
        /* wrong digest */
        if (ECDSA_verify(0, wrong_digest, 20, signature, sig_len, eckey) == 1) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        BIO_printf(out, ".");
        (void)BIO_flush(out);
        /* wrong length */
        if (ECDSA_verify(0, digest, 20, signature, sig_len - 1, eckey) == 1) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        BIO_printf(out, ".");
        (void)BIO_flush(out);

        /*
         * Modify a single byte of the signature: to ensure we don't garble
         * the ASN1 structure, we read the raw signature and modify a byte in
         * one of the bignums directly.
         */
        sig_ptr = signature;
        if ((ecdsa_sig = d2i_ECDSA_SIG(NULL, &sig_ptr, sig_len)) == NULL) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }

        /* Store the two BIGNUMs in raw_buf. */
        r_len = BN_num_bytes(ecdsa_sig->r);
        s_len = BN_num_bytes(ecdsa_sig->s);
        bn_len = (degree + 7) / 8;
        if ((r_len > bn_len) || (s_len > bn_len)) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        buf_len = 2 * bn_len;
        if ((raw_buf = OPENSSL_malloc(buf_len)) == NULL)
            goto builtin_err;
        /* Pad the bignums with leading zeroes. */
        memset(raw_buf, 0, buf_len);
        BN_bn2bin(ecdsa_sig->r, raw_buf + bn_len - r_len);
        BN_bn2bin(ecdsa_sig->s, raw_buf + buf_len - s_len);

        /* Modify a single byte in the buffer. */
        offset = raw_buf[10] % buf_len;
        dirt = raw_buf[11] ? raw_buf[11] : 1;
        raw_buf[offset] ^= dirt;
        /* Now read the BIGNUMs back in from raw_buf. */
        if ((BN_bin2bn(raw_buf, bn_len, ecdsa_sig->r) == NULL) ||
            (BN_bin2bn(raw_buf + bn_len, bn_len, ecdsa_sig->s) == NULL))
            goto builtin_err;

        sig_ptr2 = signature;
        sig_len = i2d_ECDSA_SIG(ecdsa_sig, &sig_ptr2);
        if (ECDSA_verify(0, digest, 20, signature, sig_len, eckey) == 1) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        /*
         * Sanity check: undo the modification and verify signature.
         */
        raw_buf[offset] ^= dirt;
        if ((BN_bin2bn(raw_buf, bn_len, ecdsa_sig->r) == NULL) ||
            (BN_bin2bn(raw_buf + bn_len, bn_len, ecdsa_sig->s) == NULL))
            goto builtin_err;

        sig_ptr2 = signature;
        sig_len = i2d_ECDSA_SIG(ecdsa_sig, &sig_ptr2);
        if (ECDSA_verify(0, digest, 20, signature, sig_len, eckey) != 1) {
            BIO_printf(out, " failed\n");
            goto builtin_err;
        }
        BIO_printf(out, ".");
        (void)BIO_flush(out);

        BIO_printf(out, " ok\n");
        /* cleanup */
        /* clean bogus errors */
        ERR_clear_error();
        OPENSSL_free(signature);
        signature = NULL;
        EC_KEY_free(eckey);
        eckey = NULL;
        EC_KEY_free(wrong_eckey);
        wrong_eckey = NULL;
        ECDSA_SIG_free(ecdsa_sig);
        ecdsa_sig = NULL;
        OPENSSL_free(raw_buf);
        raw_buf = NULL;
    }

    ret = 1;
 builtin_err:
    if (eckey)
        EC_KEY_free(eckey);
    if (wrong_eckey)
        EC_KEY_free(wrong_eckey);
    if (ecdsa_sig)
        ECDSA_SIG_free(ecdsa_sig);
    if (signature)
        OPENSSL_free(signature);
    if (raw_buf)
        OPENSSL_free(raw_buf);
    if (curves)
        OPENSSL_free(curves);

    return ret;
}