use the original ChaCha7539 from pointycastle.

.idea/dictionaries/herbert.xml

@@ -1,6 +1,7 @@
 <component name="ProjectDictionaryState">
   <dictionary name="herbert">
     <words>
+      <w>chacha</w>
       <w>consts</w>
       <w>derivator</w>
       <w>encrypter</w>

lib/src/crypto/protected_salt_generator.dart

@@ -3,7 +3,6 @@ import 'dart:typed_data';
 
 import 'package:logging/logging.dart';
 import 'package:crypto/crypto.dart';
-import 'package:cryptography/cryptography.dart' as cryptography;
 import 'package:pointycastle/export.dart';
 
 final _logger = Logger('protected_salt_generator');
@@ -16,7 +15,8 @@ class ProtectedSaltGenerator {
     return ProtectedSaltGenerator._(cipher);
   }
   factory ProtectedSaltGenerator.chacha20(Uint8List key) {
-    return ChachaProtectedSaltGenerator.create(key); // Chacha20();
+//    return ChachaProtectedSaltGenerator.create(key); // Chacha20();
+    return ChachaPointyCastleProtectedSaltGenerator.create(key);
   }
 
   ProtectedSaltGenerator._(this._cipher);
@@ -42,39 +42,21 @@ class ProtectedSaltGenerator {
   }
 }
 
-class ChachaProtectedSaltGenerator implements ProtectedSaltGenerator {
+class ChachaPointyCastleProtectedSaltGenerator extends ProtectedSaltGenerator {
-  ChachaProtectedSaltGenerator._(this._state);
+  ChachaPointyCastleProtectedSaltGenerator._(StreamCipher state)
+      : super._(state);
 
-  factory ChachaProtectedSaltGenerator.create(Uint8List key) {
+  factory ChachaPointyCastleProtectedSaltGenerator.create(Uint8List key) {
     final hash = sha512.convert(key);
     final secretKey = hash.bytes.sublist(0, 32);
     final nonce = hash.bytes.sublist(32, 32 + 12);
 
-    return ChachaProtectedSaltGenerator._(cryptography.chacha20.newState(
+    final chacha20 = ChaCha7539Engine()
-        cryptography.SecretKey(secretKey),
+      ..init(
-        nonce: cryptography.SecretKey(nonce)));
+          null,
-  }
+          ParametersWithIV(
-
+              KeyParameter(secretKey as Uint8List), nonce as Uint8List));
-  final cryptography.KeyStreamCipherState _state;
 
-  @override
+    return ChachaPointyCastleProtectedSaltGenerator._(chacha20);
-  StreamCipher get _cipher => throw UnimplementedError();
-
-  @override
-  String decryptBase64(String protectedValue) {
-    final bytes = base64.decode(protectedValue);
-    if (bytes.isEmpty) {
-      _logger.warning('decoded base64 data has length 0');
-      return null;
-    }
-    final result = _state.convert(bytes);
-    return utf8.decode(result);
-  }
-
-  @override
-  String encryptToBase64(String plainValue) {
-    final input = utf8.encode(plainValue) as Uint8List;
-    final encrypted = _state.convert(input);
-    return base64.encode(encrypted);
   }
 }

lib/src/kdbx_format.dart

@@ -6,7 +6,6 @@ import 'dart:typed_data';
 import 'package:argon2_ffi_base/argon2_ffi_base.dart';
 import 'package:convert/convert.dart' as convert;
 import 'package:crypto/crypto.dart' as crypto;
-import 'package:cryptography/cryptography.dart' as cryptography;
 import 'package:kdbx/kdbx.dart';
 import 'package:kdbx/src/crypto/key_encrypter_kdf.dart';
 import 'package:kdbx/src/crypto/protected_salt_generator.dart';
@@ -24,6 +23,7 @@ import 'package:kdbx/src/kdbx_xml.dart';
 import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
 import 'package:pointycastle/export.dart';
+import 'package:pointycastle/stream/chacha7539.dart';
 import 'package:xml/xml.dart' as xml;
 
 final _logger = Logger('kdbx.format');
@@ -543,9 +543,9 @@ class KdbxFormat {
   Uint8List transformContentV4ChaCha20(
       KdbxHeader header, Uint8List encrypted, Uint8List cipherKey) {
     final encryptionIv = header.fields[HeaderFields.EncryptionIV].bytes;
-    final key = cryptography.SecretKey(cipherKey);
+    final engine = ChaCha7539Engine()
-    final nonce = cryptography.SecretKey(encryptionIv);
+      ..init(false, ParametersWithIV(KeyParameter(cipherKey), encryptionIv));
-    return cryptography.chacha20.decrypt(encrypted, key, nonce: nonce);
+    return engine.process(encrypted);
   }
 
 //  Uint8List _transformDataV4Aes() {

pubspec.yaml

@@ -13,7 +13,6 @@ dependencies:
   logging: '>=0.11.3+2 <1.0.0'
   crypto: '>=2.0.0 <3.0.0'
   pointycastle: '>=1.0.1 <2.0.0'
-  cryptography: ^0.1.2
   xml: '>=4.0.0 <5.0.0'
   uuid: '>=2.0.0 <3.0.0'
   meta: '>=1.0.0 <2.0.0'
@@ -34,3 +33,15 @@ dependencies:
 dev_dependencies:
   pedantic: '>=1.7.0 <2.0.0'
   test: '>=1.6.0 <2.0.0'
+
+dependency_overrides:
+  pointycastle:
+    git:
+      url: https://github.com/bcgit/pc-dart.git
+      ref: 7c8a8b47faa75432fe3fb9a739db4a289e12b341
+#  pointycastle:
+#    git:
+#      url: https://github.com/authpass/pc-dart.git
+#      ref: 38fa40e966153b3d3cf93a9bd95228f76af3b9d7
+#  pointycastle:
+#    path: /Users/herbert/dev/pointycastle