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fix: Migrate Double Ratchet to the helper functions

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This commit is contained in:
PapaTutuWawa 2022-08-04 14:10:08 +02:00
parent 4d6dbef549
commit 31d3897995
1 changed files with 10 additions and 75 deletions
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85
lib/src/double_ratchet/crypto.dart
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@ -1,62 +1,24 @@
import 'dart:convert';
import 'package:cryptography/cryptography.dart';
import 'package:omemo_dart/protobuf/schema.pb.dart'; import 'package:omemo_dart/protobuf/schema.pb.dart';
import 'package:omemo_dart/src/crypto.dart';
import 'package:omemo_dart/src/errors.dart'; import 'package:omemo_dart/src/errors.dart';
import 'package:omemo_dart/src/helpers.dart'; import 'package:omemo_dart/src/helpers.dart';
/// Info string for ENCRYPT /// Info string for ENCRYPT
const encryptHkdfInfoString = 'OMEMO Message Key Material'; const encryptHkdfInfoString = 'OMEMO Message Key Material';
/// cryptography _really_ wants to check the MAC output from AES-256-CBC. Since
/// we don't have it, we need the MAC check to always "pass".
class NoMacSecretBox extends SecretBox {
NoMacSecretBox(super.cipherText, { required super.nonce }) : super(mac: Mac.empty);
@override
Future<void> checkMac({
required MacAlgorithm macAlgorithm,
required SecretKey secretKey,
required List<int> aad,
}) async {}
}
/// Signals ENCRYPT function as specified by OMEMO 0.8.3. /// Signals ENCRYPT function as specified by OMEMO 0.8.3.
/// Encrypt [plaintext] using the message key [mk], given associated_data [associatedData] /// Encrypt [plaintext] using the message key [mk], given associated_data [associatedData]
/// and the AD output from the X3DH [sessionAd]. /// and the AD output from the X3DH [sessionAd].
Future<List<int>> encrypt(List<int> mk, List<int> plaintext, List<int> associatedData, List<int> sessionAd) async { Future<List<int>> encrypt(List<int> mk, List<int> plaintext, List<int> associatedData, List<int> sessionAd) async {
final hkdf = Hkdf( // Generate encryption, authentication key and IV
hmac: Hmac(Sha256()), final keys = await deriveEncryptionKeys(mk, encryptHkdfInfoString);
outputLength: 80, final ciphertext = await aes256CbcEncrypt(plaintext, keys.encryptionKey, keys.iv);
);
final hkdfResult = await hkdf.deriveKey(
secretKey: SecretKey(mk),
nonce: List<int>.filled(32, 0x0),
info: utf8.encode(encryptHkdfInfoString),
);
final hkdfBytes = await hkdfResult.extractBytes();
// Split hkdfBytes into encryption, authentication key and IV
final encryptionKey = hkdfBytes.sublist(0, 32);
final authenticationKey = hkdfBytes.sublist(32, 64);
final iv = hkdfBytes.sublist(64, 80);
final aesResult = await AesCbc.with256bits(
macAlgorithm: MacAlgorithm.empty,
).encrypt(
plaintext,
secretKey: SecretKey(encryptionKey),
nonce: iv,
);
final header = OMEMOMessage.fromBuffer(associatedData.sublist(sessionAd.length)) final header = OMEMOMessage.fromBuffer(associatedData.sublist(sessionAd.length))
..ciphertext = aesResult.cipherText; ..ciphertext = ciphertext;
final headerBytes = header.writeToBuffer(); final headerBytes = header.writeToBuffer();
final hmacInput = concat([sessionAd, headerBytes]); final hmacInput = concat([sessionAd, headerBytes]);
final hmacResult = (await Hmac.sha256().calculateMac( final hmacResult = await truncatedHmac(hmacInput, keys.authenticationKey);
hmacInput,
secretKey: SecretKey(authenticationKey),
)).bytes.sublist(0, 16);
final message = OMEMOAuthenticatedMessage() final message = OMEMOAuthenticatedMessage()
..mac = hmacResult ..mac = hmacResult
..message = headerBytes; ..message = headerBytes;
@ -67,46 +29,19 @@ Future<List<int>> encrypt(List<int> mk, List<int> plaintext, List<int> associate
/// Decrypt [ciphertext] with the message key [mk], given the associated_data [associatedData] /// Decrypt [ciphertext] with the message key [mk], given the associated_data [associatedData]
/// and the AD output from the X3DH. /// and the AD output from the X3DH.
Future<List<int>> decrypt(List<int> mk, List<int> ciphertext, List<int> associatedData, List<int> sessionAd) async { Future<List<int>> decrypt(List<int> mk, List<int> ciphertext, List<int> associatedData, List<int> sessionAd) async {
// Generate the keys and iv from mk // Generate encryption, authentication key and IV
final hkdf = Hkdf( final keys = await deriveEncryptionKeys(mk, encryptHkdfInfoString);
hmac: Hmac(Sha256()),
outputLength: 80,
);
final hkdfResult = await hkdf.deriveKey(
secretKey: SecretKey(mk),
nonce: List<int>.filled(32, 0x0),
info: utf8.encode(encryptHkdfInfoString),
);
final hkdfBytes = await hkdfResult.extractBytes();
// Split hkdfBytes into encryption, authentication key and IV
final encryptionKey = hkdfBytes.sublist(0, 32);
final authenticationKey = hkdfBytes.sublist(32, 64);
final iv = hkdfBytes.sublist(64, 80);
// Assumption ciphertext is a OMEMOAuthenticatedMessage // Assumption ciphertext is a OMEMOAuthenticatedMessage
final message = OMEMOAuthenticatedMessage.fromBuffer(ciphertext); final message = OMEMOAuthenticatedMessage.fromBuffer(ciphertext);
final header = OMEMOMessage.fromBuffer(message.message); final header = OMEMOMessage.fromBuffer(message.message);
final hmacInput = concat([sessionAd, header.writeToBuffer()]); final hmacInput = concat([sessionAd, header.writeToBuffer()]);
final hmacResult = (await Hmac.sha256().calculateMac( final hmacResult = await truncatedHmac(hmacInput, keys.authenticationKey);
hmacInput,
secretKey: SecretKey(authenticationKey),
)).bytes.sublist(0, 16);
if (!listsEqual(hmacResult, message.mac)) { if (!listsEqual(hmacResult, message.mac)) {
throw InvalidMessageHMACException(); throw InvalidMessageHMACException();
} }
final plaintext = await AesCbc.with256bits( return aes256CbcDecrypt(header.ciphertext, keys.encryptionKey, keys.iv);
macAlgorithm: MacAlgorithm.empty,
).decrypt(
NoMacSecretBox(
header.ciphertext,
nonce: iv,
),
secretKey: SecretKey(encryptionKey),
);
return plaintext;
} }