+/*
+ * Verify Schnorr signature 'sig' of length 'siglen' against public exponent
+ * g_x (g^x) under group defined by 'grp_p', 'grp_q' and 'grp_g' using a
+ * SHA256 hash.
+ * Signature hash will be salted with 'idlen' bytes from 'id'.
+ * Returns -1 on failure, 0 on incorrect signature or 1 on matching signature.
+ */
+int
+schnorr_verify_buf(const BIGNUM *grp_p, const BIGNUM *grp_q,
+ const BIGNUM *grp_g,
+ const BIGNUM *g_x, const u_char *id, u_int idlen,
+ const u_char *sig, u_int siglen)
+{
+ Buffer b;
+ int ret = -1;
+ u_int rlen;
+ BIGNUM *r, *e;
+
+ e = r = NULL;
+ if ((e = BN_new()) == NULL ||
+ (r = BN_new()) == NULL) {
+ error("%s: BN_new", __func__);
+ goto out;
+ }
+
+ /* Extract g^v and r from signature blob */
+ buffer_init(&b);
+ buffer_append(&b, sig, siglen);
+ SCHNORR_DEBUG_BUF((buffer_ptr(&b), buffer_len(&b),
+ "%s: sigblob", __func__));
+ buffer_get_bignum2(&b, e);
+ buffer_get_bignum2(&b, r);
+ rlen = buffer_len(&b);
+ buffer_free(&b);
+ if (rlen != 0) {
+ error("%s: remaining bytes in signature %d", __func__, rlen);
+ goto out;
+ }
+
+ ret = schnorr_verify(grp_p, grp_q, grp_g, EVP_sha256(),
+ g_x, id, idlen, r, e);
+ out:
+ BN_clear_free(e);
+ BN_clear_free(r);
+
+ return ret;
+}
+
+/* Helper functions */
+
+/*
+ * Generate uniformly distributed random number in range (1, high).
+ * Return number on success, NULL on failure.
+ */
+BIGNUM *
+bn_rand_range_gt_one(const BIGNUM *high)
+{
+ BIGNUM *r, *tmp;
+ int success = -1;
+
+ if ((tmp = BN_new()) == NULL) {
+ error("%s: BN_new", __func__);
+ return NULL;
+ }
+ if ((r = BN_new()) == NULL) {
+ error("%s: BN_new failed", __func__);
+ goto out;
+ }
+ if (BN_set_word(tmp, 2) != 1) {
+ error("%s: BN_set_word(tmp, 2)", __func__);
+ goto out;
+ }
+ if (BN_sub(tmp, high, tmp) == -1) {
+ error("%s: BN_sub failed (tmp = high - 2)", __func__);
+ goto out;
+ }
+ if (BN_rand_range(r, tmp) == -1) {
+ error("%s: BN_rand_range failed", __func__);
+ goto out;
+ }
+ if (BN_set_word(tmp, 2) != 1) {
+ error("%s: BN_set_word(tmp, 2)", __func__);
+ goto out;
+ }
+ if (BN_add(r, r, tmp) == -1) {
+ error("%s: BN_add failed (r = r + 2)", __func__);
+ goto out;
+ }
+ success = 0;
+ out:
+ BN_clear_free(tmp);
+ if (success == 0)
+ return r;
+ BN_clear_free(r);
+ return NULL;
+}
+
+/*
+ * Hash contents of buffer 'b' with hash 'md'. Returns 0 on success,
+ * with digest via 'digestp' (caller to free) and length via 'lenp'.
+ * Returns -1 on failure.
+ */
+int
+hash_buffer(const u_char *buf, u_int len, const EVP_MD *md,
+ u_char **digestp, u_int *lenp)
+{
+ u_char digest[EVP_MAX_MD_SIZE];
+ u_int digest_len;
+ EVP_MD_CTX evp_md_ctx;
+ int success = -1;
+
+ EVP_MD_CTX_init(&evp_md_ctx);
+
+ if (EVP_DigestInit_ex(&evp_md_ctx, md, NULL) != 1) {
+ error("%s: EVP_DigestInit_ex", __func__);
+ goto out;
+ }
+ if (EVP_DigestUpdate(&evp_md_ctx, buf, len) != 1) {
+ error("%s: EVP_DigestUpdate", __func__);
+ goto out;
+ }
+ if (EVP_DigestFinal_ex(&evp_md_ctx, digest, &digest_len) != 1) {
+ error("%s: EVP_DigestFinal_ex", __func__);
+ goto out;
+ }
+ *digestp = xmalloc(digest_len);
+ *lenp = digest_len;
+ memcpy(*digestp, digest, *lenp);
+ success = 0;
+ out:
+ EVP_MD_CTX_cleanup(&evp_md_ctx);
+ bzero(digest, sizeof(digest));
+ digest_len = 0;
+ return success;
+}
+
+/* print formatted string followed by bignum */
+void
+debug3_bn(const BIGNUM *n, const char *fmt, ...)
+{
+ char *out, *h;
+ va_list args;
+
+ out = NULL;
+ va_start(args, fmt);
+ vasprintf(&out, fmt, args);
+ va_end(args);
+ if (out == NULL)
+ fatal("%s: vasprintf failed", __func__);
+
+ if (n == NULL)
+ debug3("%s(null)", out);
+ else {
+ h = BN_bn2hex(n);
+ debug3("%s0x%s", out, h);
+ free(h);
+ }
+ free(out);
+}
+
+/* print formatted string followed by buffer contents in hex */
+void
+debug3_buf(const u_char *buf, u_int len, const char *fmt, ...)
+{
+ char *out, h[65];
+ u_int i, j;
+ va_list args;
+
+ out = NULL;
+ va_start(args, fmt);
+ vasprintf(&out, fmt, args);
+ va_end(args);
+ if (out == NULL)
+ fatal("%s: vasprintf failed", __func__);
+
+ debug3("%s length %u%s", out, len, buf == NULL ? " (null)" : "");
+ free(out);
+ if (buf == NULL)
+ return;
+
+ *h = '\0';
+ for (i = j = 0; i < len; i++) {
+ snprintf(h + j, sizeof(h) - j, "%02x", buf[i]);
+ j += 2;
+ if (j >= sizeof(h) - 1 || i == len - 1) {
+ debug3(" %s", h);
+ *h = '\0';
+ j = 0;
+ }
+ }
+}
+
+/*
+ * Construct a MODP group from hex strings p (which must be a safe
+ * prime) and g, automatically calculating subgroup q as (p / 2)
+ */
+struct modp_group *
+modp_group_from_g_and_safe_p(const char *grp_g, const char *grp_p)
+{
+ struct modp_group *ret;
+
+ ret = xmalloc(sizeof(*ret));
+ ret->p = ret->q = ret->g = NULL;
+ if (BN_hex2bn(&ret->p, grp_p) == 0 ||
+ BN_hex2bn(&ret->g, grp_g) == 0)
+ fatal("%s: BN_hex2bn", __func__);
+ /* Subgroup order is p/2 (p is a safe prime) */
+ if ((ret->q = BN_new()) == NULL)
+ fatal("%s: BN_new", __func__);
+ if (BN_rshift1(ret->q, ret->p) != 1)
+ fatal("%s: BN_rshift1", __func__);
+
+ return ret;
+}
+
+void
+modp_group_free(struct modp_group *grp)
+{
+ if (grp->g != NULL)
+ BN_clear_free(grp->g);
+ if (grp->p != NULL)
+ BN_clear_free(grp->p);
+ if (grp->q != NULL)
+ BN_clear_free(grp->q);
+ bzero(grp, sizeof(*grp));
+ xfree(grp);
+}
+
+/* main() function for self-test */
+
andersk / gssapi-openssh.git / commitdiff
