Add cipher related interfaces

lib/src/cipher.dart

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+// Copyright (c) 2020
+// Author: Hugo Pointcheval
+
+import 'dart:typed_data';
+
+import 'key.dart';
+
+/// Represents different block cipher modes
+enum BlockCipherMode { ECB, CBC, CFB, GCM, CGM }
+
+/// Represents different padding
+enum Padding { ANSI_X923, PKCS5, PKCS7, None }
+
+/// Represents a cipher.
+///
+/// In cryptography, a cipher is an algorithm for performing encryption
+/// or decryption - a series of well-defined steps that can
+/// be followed as a procedure.
+abstract class Cipher {
+  /// Returns the standard algorithm name for this cipher
+  String get algorithm;
+
+  /// Returns the secret key used for this cipher
+  SecretKey get secretKey;
+
+  /// Returns the parameters used for this cipher
+  CipherParameters get parameters;
+
+  /// Returns true if cipher is initialized
+  bool get isInitialized;
+
+  /// Encrypts data.
+  ///
+  /// Takes [Uint8List] data as parameter.
+  /// Returns a [CipherText].
+  Future<CipherText> encrypt(Uint8List data);
+
+  /// Decrypts cipher text.
+  ///
+  /// Takes [CipherText] as parameter.
+  /// And returns plain text data as [Uint8List].
+  Future<Uint8List> decrypt(CipherText cipherText);
+}
+
+/// Represents a cipher text.
+///
+/// It's the result of an encryption.
+abstract class CipherText {
+  /// Returns the standard algorithm name used for this ciphertext
+  String get algorithm;
+
+  /// Returns the data of this ciphertext
+  Uint8List get bytes;
+
+  /// Returns the IV of this cipertext
+  Uint8List get iv;
+}
+
+/// Represents a pair of [BlockCipherMode] and [Padding]
+class CipherParameters {
+  BlockCipherMode _mode;
+  Padding _padding;
+
+  /// Returns mode used in the cipher
+  BlockCipherMode get mode => _mode;
+
+  /// Returns padding used in the cipher
+  Padding get padding => _padding;
+
+  CipherParameters(BlockCipherMode mode, Padding padding) {
+    _mode = mode;
+    _padding = padding;
+  }
+
+  @override
+  bool operator ==(Object o) {
+    if (identical(this, o)) return true;
+
+    return o is CipherParameters &&
+        o._mode.index == _mode.index &&
+        o._padding.index == _padding.index;
+  }
+
+  @override
+  int get hashCode => _mode.hashCode ^ _padding.hashCode;
+}