1 files changed, 56 insertions, 0 deletions
diff --git a/libmincrypt/p256_ecdsa.c b/libmincrypt/p256_ecdsa.c
new file mode 100644
index 000000000..f2264b0aa
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+++ b/libmincrypt/p256_ecdsa.c
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+/*
+ * Copyright 2013 The Android Open Source Project
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of Google Inc. nor the names of its contributors may
+ *       be used to endorse or promote products derived from this software
+ *       without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY Google Inc. ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
+ * EVENT SHALL Google Inc. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <string.h>
+
+#include "mincrypt/p256_ecdsa.h"
+#include "mincrypt/p256.h"
+
+int p256_ecdsa_verify(const p256_int* key_x, const p256_int* key_y,
+                      const p256_int* message,
+                      const p256_int* r, const p256_int* s) {
+  p256_int u, v;
+
+  // Check public key.
+  if (!p256_is_valid_point(key_x, key_y)) return 0;
+
+  // Check r and s are != 0 % n.
+  p256_mod(&SECP256r1_n, r, &u);
+  p256_mod(&SECP256r1_n, s, &v);
+  if (p256_is_zero(&u) || p256_is_zero(&v)) return 0;
+
+  p256_modinv_vartime(&SECP256r1_n, s, &v);
+  p256_modmul(&SECP256r1_n, message, 0, &v, &u);  // message / s % n
+  p256_modmul(&SECP256r1_n, r, 0, &v, &v);  // r / s % n
+
+  p256_points_mul_vartime(&u, &v,
+                          key_x, key_y,
+                          &u, &v);
+
+  p256_mod(&SECP256r1_n, &u, &u);  // (x coord % p) % n
+  return p256_cmp(r, &u) == 0;
+}
+