curve25519: Move to third_party

curve25519 comes from boringssl as well, move it to that directory.

See git log for which boringssl commit the implementation comes from,
and changes that were applied.

BRANCH=none
BUG=chromium:884905
TEST=make buildall -j, which also include basic tests.

Change-Id: I1dee4795009c1e2034a181f6083d1f9445c87d41
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1600946
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>

1 files changed, 65 insertions, 0 deletions

diff --git a/third_party/boringssl/common/curve25519.c b/third_party/boringssl/common/curve25519.c
new file mode 100644
index 0000000000..2a7fad6509
--- /dev/null
+++ b/third_party/boringssl/common/curve25519.c
@@ -0,0 +1,65 @@
+/* Copyright 2015, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+/* This code is mostly taken from the ref10 version of Ed25519 in SUPERCOP
+ * 20141124 (http://bench.cr.yp.to/supercop.html). That code is released as
+ * public domain but this file has the ISC license just to keep licencing
+ * simple.
+ *
+ * The field functions are shared by Ed25519 and X25519 where possible. */
+
+#include "common.h"
+#include "curve25519.h"
+#include "trng.h"
+#include "util.h"
+#define CRYPTO_memcmp safe_memcmp
+
+#ifdef CONFIG_RNG
+void X25519_keypair(uint8_t out_public_value[32], uint8_t out_private_key[32]) {
+  rand_bytes(out_private_key, 32);
+
+  /* All X25519 implementations should decode scalars correctly (see
+   * https://tools.ietf.org/html/rfc7748#section-5). However, if an
+   * implementation doesn't then it might interoperate with random keys a
+   * fraction of the time because they'll, randomly, happen to be correctly
+   * formed.
+   *
+   * Thus we do the opposite of the masking here to make sure that our private
+   * keys are never correctly masked and so, hopefully, any incorrect
+   * implementations are deterministically broken.
+   *
+   * This does not affect security because, although we're throwing away
+   * entropy, a valid implementation of scalarmult should throw away the exact
+   * same bits anyway. */
+  out_private_key[0] |= 7;
+  out_private_key[31] &= 63;
+  out_private_key[31] |= 128;
+
+  X25519_public_from_private(out_public_value, out_private_key);
+}
+#endif
+
+int X25519(uint8_t out_shared_key[32], const uint8_t private_key[32],
+           const uint8_t peer_public_value[32]) {
+  static const uint8_t kZeros[32] = {0};
+  x25519_scalar_mult(out_shared_key, private_key, peer_public_value);
+  /* The all-zero output results when the input is a point of small order. */
+  return CRYPTO_memcmp(kZeros, out_shared_key, 32) != 0;
+}
+
+void X25519_public_from_private(uint8_t out_public_value[32],
+                                const uint8_t private_key[32]) {
+  static const uint8_t kMongomeryBasePoint[32] = {9};
+  x25519_scalar_mult(out_public_value, private_key, kMongomeryBasePoint);
+}