104 lines
2.6 KiB
Dart
104 lines
2.6 KiB
Dart
library impl.srp_client;
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import 'dart:typed_data';
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import 'package:pointycastle/api.dart';
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import 'package:pointycastle/srp/srp6_standard_groups.dart';
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import 'package:pointycastle/srp/srp6_util.dart';
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class SRP6Client implements SRPClient {
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late BigInt N;
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late BigInt g;
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BigInt? a;
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BigInt? A;
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BigInt? B;
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BigInt? x;
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BigInt? u;
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BigInt? S;
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BigInt? M1;
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BigInt? M2;
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BigInt? Key;
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Digest digest;
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SecureRandom random;
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SRP6GroupParameters group;
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SRP6Client(
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{required this.group, required this.digest, required this.random}) {
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g = group.g;
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N = group.N;
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}
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@override
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BigInt? calculateClientEvidenceMessage() {
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// Verify pre-requirements
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if (A == null || B == null || S == null) {
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throw Exception(
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'Impossible to compute M1: some data are missing from the previous operations (A,B,S)');
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}
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// compute the client evidence message 'M1'
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M1 = SRP6Util.calculateM1(digest, N, A, B, S);
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return M1;
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}
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///S = (B - kg^x) ^ (a + ux)
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BigInt? calculateS() {
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var k = SRP6Util.calculateK(digest, N, g);
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var exp = (u! * x!) + a!;
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var tmp = g.modPow(x!, N) * (k % N);
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return (B! - (tmp % N)).modPow(exp, N);
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}
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@override
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BigInt? calculateSecret(BigInt serverB) {
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B = SRP6Util.validatePublicValue(N, serverB);
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u = SRP6Util.calculateU(digest, N, A, B);
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S = calculateS();
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return S;
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}
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@override
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BigInt? calculateSessionKey() {
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// Verify pre-requirements (here we enforce a previous calculation of M1 and M2)
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if (S == null || M1 == null || M2 == null) {
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throw Exception(
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'Impossible to compute Key: some data are missing from the previous operations (S,M1,M2)');
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}
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Key = SRP6Util.calculateKey(digest, N, S!);
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return Key;
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}
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@override
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BigInt? generateClientCredentials(
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Uint8List salt, Uint8List identity, Uint8List password) {
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x = SRP6Util.calculateX(digest, N, salt, identity, password);
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a = selectPrivateValue();
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A = g.modPow(a!, N);
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return A;
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}
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BigInt? selectPrivateValue() {
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return SRP6Util.generatePrivateValue(digest, N, g, random);
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}
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@override
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bool verifyServerEvidenceMessage(BigInt serverM2) {
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// Verify pre-requirements
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if (A == null || M1 == null || S == null) {
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throw Exception('Impossible to compute and verify M2: '
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'some data are missing from the previous operations (A,M1,S)');
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}
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// Compute the own server evidence message 'M2'
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var computedM2 = SRP6Util.calculateM2(digest, N, A, M1, S);
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if (computedM2.compareTo(serverM2) == 0) {
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M2 = serverM2;
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return true;
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}
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return false;
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}
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}
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