Add an AES encryption and decryption example

example/aes.dart

@@ -0,0 +1,48 @@
+library example.aes;
+
+import "dart:convert";
+import "dart:typed_data";
+
+import "package:hex/hex.dart";
+import "package:pointycastle/pointycastle.dart";
+
+void main() {
+  // Key must be multiple of block size (16 bytes).
+  var key = new Digest("SHA-256").process(
+      utf8.encode("correct horse battery staple"));
+  // Can be anything.
+  var message = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed d"
+      "o eiusmod tempor incididunt ut labore et dolore magna aliqua.";
+  // The initialization vector must be unique for every message, so it is a
+  // good idea to use a message digest as the IV.
+  // IV must be equal to block size (16 bytes).
+  var iv = new Digest("SHA-256").process(utf8.encode(message)).sublist(0, 16);
+  // The parameters your cipher will need. (PKCS7 does not need params.)
+  CipherParameters params = new PaddedBlockCipherParameters(
+      new ParametersWithIV(new KeyParameter(key), iv), null);
+
+  print("Message: \n$message");
+
+  ////////////////
+  // Encrypting //
+  ////////////////
+
+  // As for why you would need CBC mode and PKCS7 padding, consult the internet
+  // (f.e. http://www.di-mgt.com.au/properpassword.html).
+  BlockCipher encryptionCipher = new PaddedBlockCipher("AES/CBC/PKCS7");
+  encryptionCipher.init(true, params);
+  Uint8List encrypted = encryptionCipher.process(utf8.encode(message));
+
+  print("Encrypted: \n" + HEX.encode(encrypted));
+
+
+  ////////////////
+  // Decrypting //
+  ////////////////
+
+  BlockCipher decryptionCipher = new PaddedBlockCipher("AES/CBC/PKCS7");
+  decryptionCipher.init(false, params);
+  String decrypted = utf8.decode(decryptionCipher.process(encrypted));
+
+  print("Decrypted: \n$decrypted");
+}

pubspec.yaml

@@ -12,6 +12,7 @@ dev_dependencies:
   build_runner: ^0.10.0
   build_test: ^0.10.2
   build_web_compilers: ^0.4.0
+  hex: ">=0.1.1 <1.0.0"
   matcher: ">=0.12.0 <0.13.0"
   test: ">=0.12.30 <1.4.0"
   analyzer: "0.32.4"