101 lines
2.3 KiB
Dart
101 lines
2.3 KiB
Dart
library impl.srp_server;
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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 SRP6Server implements SRPServer {
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late BigInt N;
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late BigInt g;
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BigInt v;
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SecureRandom random;
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Digest digest;
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BigInt? A;
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BigInt? b;
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BigInt? B;
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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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SRP6Server(
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{required SRP6GroupParameters group,
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required this.v,
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required this.digest,
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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? calculateSecret(BigInt clientA) {
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A = SRP6Util.validatePublicValue(N, clientA);
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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? calculateServerEvidenceMessage() {
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// Verify pre-requirements
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if (A == null || M1 == null || S == null) {
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throw Exception(
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'Impossible to compute M2: some data are missing from the previous operations (A,M1,S)');
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}
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// Compute the server evidence message 'M2'
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M2 = SRP6Util.calculateM2(digest, N, A!, M1!, S!);
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return M2;
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}
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@override
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BigInt? calculateSessionKey() {
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// Verify pre-requirements
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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? generateServerCredentials() {
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var k = SRP6Util.calculateK(digest, N, g);
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b = selectPrivateValue();
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B = (k * v + g.modPow(b!, N)) % N;
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return B;
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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 verifyClientEvidenceMessage(BigInt clientM1) {
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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 and verify M1: some data are missing from the previous operations (A,B,S)');
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}
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// Compute the own client evidence message 'M1'
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var computedM1 = SRP6Util.calculateM1(digest, N, A, B, S);
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if (computedM1.compareTo(clientM1) == 0) {
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M1 = clientM1;
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return true;
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}
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return false;
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}
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BigInt _calculateS() {
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return ((v.modPow(u!, N) * A!) % N).modPow(b!, N);
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}
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}
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