Add SecureMessage definitions to CryptAuth.

components/proximity_auth/cryptauth/proto/securemessage.proto

+// Copyright 2015 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.
+
+// Definitions related to the SecureMessage format, used by CryptAuth. Do not
+// edit unless transcribing from server definitions.
+syntax = "proto2";
+
+package securemessage;
+
+option optimize_for = LITE_RUNTIME;
+
+message SecureMessage {
+  // Must contain a HeaderAndBody message.
+  required bytes header_and_body = 1;
+  // Signature of header_and_body.
+  required bytes signature = 2;
+}
+
+// Supported "signature" schemes (both symmetric key and public key based).
+enum SigScheme {
+  HMAC_SHA256 = 1;
+  ECDSA_P256_SHA256 = 2;
+  // Not recommended -- use ECDSA_P256_SHA256 instead
+  RSA2048_SHA256 = 3;
+}
+
+// Supported encryption schemes.
+enum EncScheme {
+  // No encryption.
+  NONE = 1;
+  AES_256_CBC = 2;
+}
+
+message Header {
+  required SigScheme signature_scheme = 1;
+  required EncScheme encryption_scheme = 2;
+  // Identifies the verification key.
+  optional bytes verification_key_id = 3;
+  // Identifies the decryption key.
+  optional bytes decryption_key_id = 4;
+  // Encryption may use an IV.
+  optional bytes iv = 5;
+  // Arbitrary per-protocol public data, to be sent with the plain-text header.
+  optional bytes public_metadata = 6;
+  // The length of some associated data this is not sent in this SecureMessage,

[Ilya Sherman, 2015/04/03 02:13:05]

nit: s/this/that?

[Tim Song, 2015/04/03 02:46:34]

Done. This is copied from the server .proto file.

+  // but which will be bound to the signature.
+  optional uint32 associated_data_length = 7 [default = 0];
+}
+
+message HeaderAndBody {
+  // Public data about this message (to be bound in the signature).
+  required Header header = 1;
+  // Payload data.
+  required bytes body = 2;
+}
+
+// A list of supported public key types.
+enum PublicKeyType {
+  EC_P256 = 1;
+  RSA2048 = 2;
+  // 2048-bit MODP group 14, from RFC 3526.
+  DH2048_MODP = 3;
+}
+
+// A convenience proto for encoding NIST P-256 elliptic curve public keys.
+message EcP256PublicKey {
+  // x and y are encoded in big-endian two's complement (slightly wasteful)
+  // Client MUST verify (x,y) is a valid point on NIST P256.
+  required bytes x = 1;
+  required bytes y = 2;
+}
+
+// A convenience proto for encoding RSA public keys with small exponents.
+message SimpleRsaPublicKey {
+  // Encoded in big-endian two's complement.
+  required bytes n = 1;
+  optional int32 e = 2 [default = 65537];
+}
+
+// A convenience proto for encoding Diffie-Hellman public keys,
+// for use only when Elliptic Curve based key exchanges are not possible.
+// (Note that the group parameters must be specified separately).
+message DhPublicKey {
+  // Big-endian two's complement encoded group element.
+  required bytes y = 1;
+}
+
+message GenericPublicKey {
+  required PublicKeyType type = 1;
+  optional EcP256PublicKey ec_p256_public_key = 2;
+  optional SimpleRsaPublicKey rsa2048_public_key = 3;
+  // Use only as a last resort.
+  optional DhPublicKey dh2048_public_key = 4;
+}