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// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Proto definitions for SecureMessage format
syntax = "proto2";
package securemessage;
option optimize_for = LITE_RUNTIME;
option java_package = "com.google.security.cryptauth.lib.securemessage";
option java_outer_classname = "SecureMessageProto";
option objc_class_prefix = "SMSG";
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,
// 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;
}
// Must be kept wire-format compatible with HeaderAndBody. Provides the
// SecureMessage code with a consistent wire-format representation that
// remains stable irrespective of protobuf implementation choices. This
// low-level representation of a HeaderAndBody should not be used by
// any code outside of the SecureMessage library implementation/tests.
message HeaderAndBodyInternal {
// A raw (wire-format) byte encoding of a Header, suitable for hashing
required bytes header = 1;
// Payload data
required bytes body = 2;
}
// -------
// The remainder of the messages defined here are provided only for
// convenience. They are not needed for SecureMessage proper, but are
// commonly useful wherever SecureMessage might be applied.
// -------
// 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;
}
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