refactor: Clean up the X3DH implementation
This commit is contained in:
42
lib/src/bundle.dart
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42
lib/src/bundle.dart
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import 'dart:convert';
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import 'package:cryptography/cryptography.dart';
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import 'key.dart';
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class OmemoBundle {
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const OmemoBundle(
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this.id,
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this.spkEncoded,
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this.spkId,
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this.spkSignatureEncoded,
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this.ikEncoded,
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this.opksEncoded,
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);
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final String id;
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/// The SPK but base64 encoded
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final String spkEncoded;
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final String spkId;
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/// The SPK signature but base64 encoded
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final String spkSignatureEncoded;
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/// The IK but base64 encoded
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final String ikEncoded;
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/// The mapping of a OPK's id to the base64 encoded data
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final Map<String, String> opksEncoded;
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OmemoPublicKey get spk {
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final data = base64Decode(spkEncoded);
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return OmemoPublicKey.fromBytes(data, KeyPairType.x25519);
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}
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OmemoPublicKey get ik {
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final data = base64Decode(ikEncoded);
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return OmemoPublicKey.fromBytes(data, KeyPairType.ed25519);
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}
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OmemoPublicKey getOpk(String id) {
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final data = base64Decode(opksEncoded[id]!);
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return OmemoPublicKey.fromBytes(data, KeyPairType.x25519);
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}
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List<int> get spkSignature => base64Decode(spkSignatureEncoded);
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}
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123
lib/src/key.dart
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123
lib/src/key.dart
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import 'dart:convert';
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import 'package:cryptography/cryptography.dart';
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import 'package:pinenacl/api.dart';
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import 'package:pinenacl/tweetnacl.dart';
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const privateKeyLength = 32;
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const publicKeyLength = 32;
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class OmemoPublicKey {
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const OmemoPublicKey(this._pubkey);
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final SimplePublicKey _pubkey;
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factory OmemoPublicKey.fromBytes(List<int> bytes, KeyPairType type) {
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return OmemoPublicKey(
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SimplePublicKey(
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bytes,
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type: type,
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),
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);
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}
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KeyPairType get type => _pubkey.type;
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/// Return the bytes that comprise the public key.
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Future<List<int>> getBytes() async => _pubkey.bytes;
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/// Returns the public key encoded as base64.
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Future<String> asBase64() async => base64Encode(_pubkey.bytes);
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Future<OmemoPublicKey> toCurve25519() async {
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assert(type == KeyPairType.ed25519, 'Cannot convert non-Ed25519 public key to X25519');
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final pkc = Uint8List(publicKeyLength);
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TweetNaClExt.crypto_sign_ed25519_pk_to_x25519_pk(
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pkc,
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Uint8List.fromList(await getBytes()),
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);
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return OmemoPublicKey(SimplePublicKey(List<int>.from(pkc), type: KeyPairType.x25519));
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}
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SimplePublicKey asPublicKey() => _pubkey;
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/// Convert the public key into a [SimpleKeyPairData] with a stub private key. Useful
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/// for when cryptography calls for a KeyPair, but only uses the public key.
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//SimpleKeyPairData asPseudoKeypair() {
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//
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//}
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}
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class OmemoPrivateKey {
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const OmemoPrivateKey(this._privkey, this.type);
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final List<int> _privkey;
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final KeyPairType type;
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Future<List<int>> getBytes() async => _privkey;
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Future<OmemoPrivateKey> toCurve25519() async {
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assert(type == KeyPairType.ed25519, 'Cannot convert non-Ed25519 private key to X25519');
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final skc = Uint8List(privateKeyLength);
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TweetNaClExt.crypto_sign_ed25519_sk_to_x25519_sk(
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skc,
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Uint8List.fromList(await getBytes()),
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);
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return OmemoPrivateKey(List<int>.from(skc), KeyPairType.x25519);
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}
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}
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/// A generic wrapper class for both Ed25519 and X25519 keypairs
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class OmemoKeyPair {
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const OmemoKeyPair(this.pk, this.sk, this.type);
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final KeyPairType type;
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final OmemoPublicKey pk;
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final OmemoPrivateKey sk;
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static Future<OmemoKeyPair> generateNewPair(KeyPairType type) async {
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assert(type == KeyPairType.ed25519 || type == KeyPairType.x25519);
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SimpleKeyPair kp;
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if (type == KeyPairType.ed25519) {
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final ed = Ed25519();
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kp = await ed.newKeyPair();
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} else if (type == KeyPairType.x25519) {
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final x = Cryptography.instance.x25519();
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kp = await x.newKeyPair();
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} else {
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// Should never happen
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throw Exception();
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}
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final kpd = await kp.extract();
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return OmemoKeyPair(
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OmemoPublicKey(await kp.extractPublicKey()),
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OmemoPrivateKey(await kpd.extractPrivateKeyBytes(), type),
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type,
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);
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}
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/// Return the bytes that comprise the public key.
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Future<OmemoKeyPair> toCurve25519() async {
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assert(type == KeyPairType.ed25519, 'Cannot convert non-Ed25519 keypair to X25519');
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return OmemoKeyPair(
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await pk.toCurve25519(),
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await sk.toCurve25519(),
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KeyPairType.x25519,
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);
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}
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Future<SimpleKeyPairData> asKeyPair() async {
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return SimpleKeyPairData(
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await sk.getBytes(),
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publicKey: pk.asPublicKey(),
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type: type,
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);
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}
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}
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122
lib/src/x3dh.dart
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122
lib/src/x3dh.dart
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@@ -0,0 +1,122 @@
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import 'dart:convert';
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import 'dart:math';
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import 'package:cryptography/cryptography.dart';
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import 'bundle.dart';
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import 'key.dart';
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/// The overarching assumption is that we use Ed25519 keys for the identity keys
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/// Performed by Alice
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class X3DHResult {
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const X3DHResult(this.ek, this.sk, this.opkId);
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final OmemoKeyPair ek;
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final List<int> sk;
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final String opkId;
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}
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/// Received by Bob
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class X3DHMessage {
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const X3DHMessage(this.ik, this.ek, this.opkId);
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final OmemoPublicKey ik;
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final OmemoPublicKey ek;
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final String opkId;
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}
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/// Sign [message] using the keypair [keyPair]. Note that [keyPair] must be
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/// a Ed25519 keypair.
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Future<List<int>> sig(OmemoKeyPair keyPair, List<int> message) async {
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assert(keyPair.type == KeyPairType.ed25519);
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final signature = await Ed25519().sign(
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message,
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keyPair: await keyPair.asKeyPair(),
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);
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return signature.bytes;
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}
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/// Performs X25519 with [pk1] and [pk2]. If [identityKey] is set, then
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/// it indicates which of [pk1] ([identityKey] == 1) or [pk2] ([identityKey] == 2)
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/// is the identity key.
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Future<List<int>> dh(OmemoKeyPair kp, OmemoPublicKey pk, int identityKey) async {
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var ckp = kp;
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var cpk = pk;
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if (identityKey == 1) {
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ckp = await kp.toCurve25519();
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} else if (identityKey == 2) {
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cpk = await pk.toCurve25519();
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}
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final shared = await Cryptography.instance.x25519().sharedSecretKey(
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keyPair: await ckp.asKeyPair(),
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remotePublicKey: cpk.asPublicKey(),
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);
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return shared.extractBytes();
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}
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/// Derive a secret from the key material [km].
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Future<List<int>> kdf(List<int> km) async {
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final f = List<int>.filled(32, 0xFF);
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final input = List<int>.empty(growable: true);
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input
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..addAll(f)
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..addAll(km);
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final algorithm = Hkdf(
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hmac: Hmac(Sha256()),
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outputLength: 32,
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);
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final output = await algorithm.deriveKey(
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secretKey: SecretKey(input),
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// TODO: Fix
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nonce: List<int>.filled(32, 0x00),
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info: utf8.encode('OMEMO X3DH'),
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);
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return output.extractBytes();
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}
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/// Flattens [inputs] and concatenates the elements.
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List<int> concat(List<List<int>> inputs) {
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final tmp = List<int>.empty(growable: true);
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for (final input in inputs) {
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tmp.addAll(input);
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}
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return tmp;
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}
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/// Alice builds a session with Bob using his bundle [bundle] and Alice's identity key
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/// pair [ika].
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Future<X3DHResult> x3dhFromBundle(OmemoBundle bundle, OmemoKeyPair ik) async {
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// Generate EK
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final ek = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
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final random = Random.secure();
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final opkIndex = random.nextInt(bundle.opksEncoded.length);
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final opkId = bundle.opksEncoded.keys.elementAt(opkIndex);
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final opk = bundle.getOpk(opkId);
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final dh1 = await dh(ik, bundle.spk, 1);
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final dh2 = await dh(ek, bundle.ik, 2);
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final dh3 = await dh(ek, bundle.spk, 0);
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final dh4 = await dh(ek, opk, 0);
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final sk = await kdf(concat([dh1, dh2, dh3, dh4]));
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return X3DHResult(ek, sk, opkId);
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}
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/// Bob builds the X3DH shared secret from the inital message [msg], the SPK [spk], the
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/// OPK [opk] that was selected by Alice and our IK [ik]. Returns the shared secret.
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Future<List<int>> x3dhFromInitialMessage(X3DHMessage msg, OmemoKeyPair spk, OmemoKeyPair opk, OmemoKeyPair ik) async {
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final dh1 = await dh(spk, msg.ik, 2);
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final dh2 = await dh(ik, msg.ek, 1);
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final dh3 = await dh(spk, msg.ek, 0);
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final dh4 = await dh(opk, msg.ek, 0);
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return kdf(concat([dh1, dh2, dh3, dh4]));
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}
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@@ -1,125 +0,0 @@
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import 'dart:convert';
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import 'dart:typed_data';
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import 'package:cryptography/cryptography.dart';
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import 'package:pinenacl/api.dart';
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import 'package:pinenacl/tweetnacl.dart';
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/// The overarching assumption is that we use Ed25519 keys for the identity keys
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class X3DHRun {
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const X3DHRun(this.epk, this.sharedSecret);
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final SimpleKeyPair epk;
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final List<int> sharedSecret;
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}
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SimpleKeyPairData fromPublicKey(SimplePublicKey pk) {
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return SimpleKeyPairData([], publicKey: pk, type: KeyPairType.x25519);
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}
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Future<List<int>> sig(SimpleKeyPair keyPair, List<int> message) async {
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final signature = await Ed25519().sign(
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message,
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keyPair: keyPair,
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);
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return signature.bytes;
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}
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/// Performs X25519 with [pk1] and [pk2]. If [identityKey] is set, then
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/// it indicates which of [pk1] ([identityKey] == 1) or [pk2] ([identityKey] == 2)
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/// is the identity key.
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Future<List<int>> dh(SimpleKeyPair kp, SimplePublicKey pk, int identityKey) async {
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var ckp = kp;
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var cpk = pk;
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if (identityKey == 1) {
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final pubkeyBytes = (await kp.extractPublicKey()).bytes;
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final pkc = Uint8List(32);
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TweetNaClExt.crypto_sign_ed25519_pk_to_x25519_pk(pkc, Uint8List.fromList(pubkeyBytes));
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final keyPairData = await kp.extract();
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final privateKeyBytes = await keyPairData.extractPrivateKeyBytes();
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final skc = Uint8List(32);
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TweetNaClExt.crypto_sign_ed25519_sk_to_x25519_sk(skc, Uint8List.fromList(privateKeyBytes));
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ckp = SimpleKeyPairData(
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List<int>.from(skc),
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publicKey: SimplePublicKey(List<int>.from(pkc), type: KeyPairType.x25519),
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type: KeyPairType.x25519,
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);
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} else if (identityKey == 2) {
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final pubkeyBytes = pk.bytes;
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final pkc = Uint8List(32);
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TweetNaClExt.crypto_sign_ed25519_pk_to_x25519_pk(pkc, Uint8List.fromList(pubkeyBytes));
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cpk = SimplePublicKey(
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List<int>.from(pkc),
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type: KeyPairType.x25519,
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);
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}
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final shared = await Cryptography.instance.x25519().sharedSecretKey(
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keyPair: ckp,
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remotePublicKey: cpk,
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);
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return shared.extractBytes();
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}
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Future<List<int>> kdf(List<int> km) async {
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final f = List<int>.filled(32, 0xFF);
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final input = List<int>.empty(growable: true);
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input
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..addAll(f)
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..addAll(km);
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final algorithm = Hkdf(
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hmac: Hmac(Sha256()),
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outputLength: 32,
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);
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final output = await algorithm.deriveKey(
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secretKey: SecretKey(input),
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// TODO: Fix
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nonce: List<int>.filled(32, 0x00),
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info: utf8.encode('OMEMO X3DH'),
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);
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return output.extractBytes();
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}
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List<int> concat(List<List<int>> inputs) {
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final tmp = List<int>.empty(growable: true);
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for (final input in inputs) {
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tmp.addAll(input);
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}
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return tmp;
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}
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// Alice -> Bob
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Future<X3DHRun> x3dhFromPrekeyBundle(SimplePublicKey ikb, SimplePublicKey spkb, SimplePublicKey opkb, SimpleKeyPair ika) async {
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// Generate EPK
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final epk = await Cryptography.instance.x25519().newKeyPair();
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final dh1 = await dh(ika, spkb, 1);
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final dh2 = await dh(epk, ikb, 2);
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final dh3 = await dh(epk, spkb, 0);
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final dh4 = await dh(epk, opkb, 0);
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final sk = await kdf(concat([dh1, dh2, dh3, dh4]));
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return X3DHRun(
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epk,
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sk,
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);
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}
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Future<List<int>> x3dhFromInitialMessage(SimplePublicKey ika, SimplePublicKey epk, SimpleKeyPair opkb, SimpleKeyPair spk, SimpleKeyPair ikb) async {
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final dh1 = await dh(spk, ika, 2);
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final dh2 = await dh(ikb, epk, 1);
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final dh3 = await dh(spk, epk, 0);
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final dh4 = await dh(opkb, epk, 0);
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return kdf(concat([dh1, dh2, dh3, dh4]));
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}
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