C# Documentation

Tony Arcieri edited this page Dec 29, 2017 · 1 revision

Symmetric Encryption (AEAD)

The Miscreant.Aead class provides the main interface to the AES-SIV misuse resistant authenticated encryption function.

public static Aead CreateAesCmacSiv(byte[] key)
public static Aead CreateAesPmacSiv(byte[] key)

To make a new AES-SIV instance that uses CMAC, call the CreateAesCmacSiv method with a 32-byte or 64-byte key. To make a new AES-SIV instance that uses PMAC, call the CreateAesPmacSiv method with a 32-byte or 64-byte key. Note that these keys are twice the size of what you might be expecting (AES-SIV uses two AES keys).

You can generate random 32-byte or 64-byte keys using the static Aead.GenerateKey256 or Aead.GenerateKey512 methods:

var key = Aead.GenerateKey256();
var siv = Aead.CreateAesCmacSiv(key);

Encryption (Seal)

public byte[] Seal(byte[] plaintext, byte[] nonce = null, byte[] data = null)

The Seal method encrypts a message along with a set of associated data which acts as message headers.

It's recommended to include a unique "nonce" value with each message. This prevents those who may be observing your ciphertexts from being able to tell if you encrypted the same message twice. However, unlike other cryptographic algorithms where using a nonce has catastrophic security implications such as key recovery, reusing a nonce with AES-SIV only leaks repeated ciphertexts to attackers.

Decryption (Open)

public byte[] Open(byte[] ciphertext, byte[] nonce = null, byte[] data = null)

The Open method decrypts a ciphertext with the given key.

Example

// Plaintext to encrypt.
var plaintext = "I'm cooking MC's like a pound of bacon";

// Create a 32-byte key.
var key = Aead.GenerateKey256();

// Create a 16-byte nonce (optional).
var nonce = Aead.GenerateNonce(16);

// Create a new AEAD instance using the AES-CMAC-SIV
// algorithm. It implements the IDisposable interface,
// so it's best to create it inside using statement.
using (var aead = Aead.CreateAesCmacSiv(key))
{
  // If the message is string, convert it to byte array first.
  var bytes = Encoding.UTF8.GetBytes(plaintext);

  // Encrypt the message.
  var ciphertext = aead.Seal(bytes, nonce);

  // To decrypt the message, call the Open method with the
  // ciphertext and the same nonce that you generated previously.
  bytes = aead.Open(ciphertext, nonce);

  // If the message was originally string,
  // convert if from byte array to string.
  plaintext = Encoding.UTF8.GetString(bytes);

  // Print the decrypted message to the standard output.
  Console.WriteLine(plaintext);
}
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