1 files changed, 89 insertions, 0 deletions
diff --git a/chromium/device/fido/ed25519_public_key.cc b/chromium/device/fido/ed25519_public_key.cc
new file mode 100644
index 00000000000..ff86b9e7c8f
--- /dev/null
+++ b/chromium/device/fido/ed25519_public_key.cc
@@ -0,0 +1,89 @@
+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "device/fido/ed25519_public_key.h"
+
+#include <utility>
+
+#include "components/cbor/writer.h"
+#include "device/fido/cbor_extract.h"
+#include "device/fido/fido_constants.h"
+#include "third_party/boringssl/src/include/openssl/bn.h"
+#include "third_party/boringssl/src/include/openssl/bytestring.h"
+#include "third_party/boringssl/src/include/openssl/evp.h"
+#include "third_party/boringssl/src/include/openssl/mem.h"
+#include "third_party/boringssl/src/include/openssl/obj.h"
+#include "third_party/boringssl/src/include/openssl/rsa.h"
+
+using device::cbor_extract::IntKey;
+using device::cbor_extract::Is;
+using device::cbor_extract::StepOrByte;
+using device::cbor_extract::Stop;
+
+namespace device {
+
+// static
+std::unique_ptr<PublicKey> Ed25519PublicKey::ExtractFromCOSEKey(
+    int32_t algorithm,
+    base::span<const uint8_t> cbor_bytes,
+    const cbor::Value::MapValue& map) {
+  // See https://tools.ietf.org/html/rfc8152#section-13.2
+  struct COSEKey {
+    const int64_t* kty;
+    const int64_t* crv;
+    const std::vector<uint8_t>* key;
+  } cose_key;
+
+  static constexpr cbor_extract::StepOrByte<COSEKey> kSteps[] = {
+      // clang-format off
+      ELEMENT(Is::kRequired, COSEKey, kty),
+      IntKey<COSEKey>(static_cast<int>(CoseKeyKey::kKty)),
+
+      ELEMENT(Is::kRequired, COSEKey, crv),
+      IntKey<COSEKey>(static_cast<int>(CoseKeyKey::kEllipticCurve)),
+
+      ELEMENT(Is::kRequired, COSEKey, key),
+      IntKey<COSEKey>(static_cast<int>(CoseKeyKey::kEllipticX)),
+
+      Stop<COSEKey>(),
+      // clang-format on
+  };
+
+  if (!cbor_extract::Extract<COSEKey>(&cose_key, kSteps, map) ||
+      *cose_key.kty != static_cast<int64_t>(CoseKeyTypes::kOKP) ||
+      *cose_key.crv != static_cast<int64_t>(CoseCurves::kEd25519) ||
+      cose_key.key->size() != 32) {
+    return nullptr;
+  }
+
+  // The COSE RFC says that "This contains the x-coordinate for the EC point".
+  // The RFC authors do not appear to understand what's going on because it
+  // actually just contains the Ed25519 public key, which you would expect, and
+  // which also encodes the y-coordinate as a sign bit.
+  //
+  // We could attempt to check whether |key| contains a quadratic residue, as it
+  // should. But that would involve diving into the guts of Ed25519 too much.
+
+  bssl::UniquePtr<EVP_PKEY> pkey(
+      EVP_PKEY_new_raw_public_key(EVP_PKEY_ED25519, /*engine=*/nullptr,
+                                  cose_key.key->data(), cose_key.key->size()));
+  if (!pkey) {
+    return nullptr;
+  }
+
+  bssl::ScopedCBB cbb;
+  uint8_t* der_bytes = nullptr;
+  size_t der_bytes_len = 0;
+  CHECK(CBB_init(cbb.get(), /* initial size */ 128) &&
+        EVP_marshal_public_key(cbb.get(), pkey.get()) &&
+        CBB_finish(cbb.get(), &der_bytes, &der_bytes_len));
+
+  std::vector<uint8_t> der_bytes_vec(der_bytes, der_bytes + der_bytes_len);
+  OPENSSL_free(der_bytes);
+
+  return std::make_unique<PublicKey>(algorithm, cbor_bytes,
+                                     std::move(der_bytes_vec));
+}
+
+}  // namespace device