}// Decrypt()
public static byte[] Decrypt(byte[] masterKey, ArraySegment<byte> ciphertext, ArraySegment<byte>? salt = null, uint counter = 1)
{
int cipherLength = ciphertext.Count - CONTEXT_BUFFER_LENGTH - MAC_LENGTH;
if (cipherLength < Cipher.AesConstants.AES_BLOCK_SIZE) return null;
try
{
Kdf.SP800_108_Ctr.DeriveKey(hmacFactory: _hmacFactory, key: masterKey, label: salt, context: new ArraySegment<byte>(ciphertext.Array, ciphertext.Offset, CONTEXT_BUFFER_LENGTH), derivedOutput: _sessionKey.Value.AsArraySegment(), counter: counter);
Utils.BlockCopy(_sessionKey.Value, 0, _macKey.Value, 0, MAC_KEY_LENGTH);
using (var hmac = _hmacFactory())
{
hmac.Key = _macKey.Value;
hmac.TransformBlock(ciphertext.Array, ciphertext.Offset + CONTEXT_TWEAK_LENGTH, AES_IV_LENGTH + cipherLength, null, 0);
hmac.TransformFinalBlock(ciphertext.Array, 0, 0);
var fullmacActual = hmac.HashInner;
if (!Utils.ConstantTimeEqual(fullmacActual, 0, ciphertext.Array, ciphertext.Offset + ciphertext.Count - MAC_LENGTH, MAC_LENGTH)) return null;
}// using hmac
Utils.BlockCopy(ciphertext.Array, ciphertext.Offset + CONTEXT_TWEAK_LENGTH, _iv.Value, 0, AES_IV_LENGTH);
Utils.BlockCopy(_sessionKey.Value, MAC_KEY_LENGTH, _encKey.Value, 0, ENC_KEY_LENGTH);
using (var aes = _aesFactory())
{
EtM_CBC.ValidateAes(aes);
using (var aesDecryptor = aes.CreateDecryptor(_encKey.Value, _iv.Value))
{
return aesDecryptor.TransformFinalBlock(ciphertext.Array, ciphertext.Offset + CONTEXT_BUFFER_LENGTH, cipherLength);
}// using aesDecryptor
}// using aes
}
finally { EtM_CBC.ClearKeyMaterial(); }
}// Decrypt()
}// Encrypt()
public static byte[] Encrypt(byte[] masterKey, ArraySegment<byte> plaintext, ArraySegment<byte>? salt = null, uint counter = 1)
{
int fullBlockLength = plaintext.Count & (-Cipher.AesConstants.AES_BLOCK_SIZE);
int finalBlockLength = plaintext.Count % Cipher.AesConstants.AES_BLOCK_SIZE;
int paddingLength = Cipher.AesConstants.AES_BLOCK_SIZE - finalBlockLength;
int ciphertextLength = CONTEXT_BUFFER_LENGTH + plaintext.Count + paddingLength + MAC_LENGTH;
byte[] buffer = new byte[ciphertextLength];
EtM_CBC.Encrypt(masterKey: masterKey, plaintext: plaintext, output: buffer, outputOffset: 0, salt: salt, counter: counter);
return buffer;
}// Encrypt()
}// Encrypt()
public static void Decrypt(byte[] masterKey, ArraySegment<byte> ciphertext, ref ArraySegment<byte>? outputSegment, ArraySegment<byte>? salt = null, uint counter = 1)
{
int cipherLength = ciphertext.Count - CONTEXT_BUFFER_LENGTH - MAC_LENGTH;
if (cipherLength < Cipher.AesConstants.AES_BLOCK_SIZE) { outputSegment = null; return; }
int fullBlockLength = cipherLength - AES_IV_LENGTH;
byte[] finalBlock = null;
try
{
var iv = _iv.Value;
var encKey = _encKey.Value;
var macKey = _macKey.Value;
var sessionKey = _sessionKey.Value;
Kdf.SP800_108_Ctr.DeriveKey(hmacFactory: _hmacFactory, key: masterKey, label: salt, context: new ArraySegment<byte>(ciphertext.Array, ciphertext.Offset, CONTEXT_BUFFER_LENGTH), derivedOutput: sessionKey.AsArraySegment(), counter: counter);
Utils.BlockCopy(sessionKey, 0, macKey, 0, MAC_KEY_LENGTH);
using (var hmac = _hmacFactory())
{
hmac.Key = macKey;
hmac.TransformBlock(ciphertext.Array, ciphertext.Offset + CONTEXT_TWEAK_LENGTH, AES_IV_LENGTH + cipherLength, null, 0);
hmac.TransformFinalBlock(ciphertext.Array, 0, 0);
var fullmacActual = hmac.HashInner;
if (!Utils.ConstantTimeEqual(fullmacActual, 0, ciphertext.Array, ciphertext.Offset + ciphertext.Count - MAC_LENGTH, MAC_LENGTH)) { outputSegment = null; return; };
}// using hmac
Utils.BlockCopy(ciphertext.Array, ciphertext.Offset + CONTEXT_TWEAK_LENGTH, iv, 0, AES_IV_LENGTH);
Utils.BlockCopy(sessionKey, MAC_KEY_LENGTH, encKey, 0, ENC_KEY_LENGTH);
using (var aes = _aesFactory())
{
EtM_CBC.ValidateAes(aes);
using (var aesDecryptor = aes.CreateDecryptor(encKey, iv))
{
int fullBlockTransformed = 0;
if (fullBlockLength > 0)
fullBlockTransformed = aesDecryptor.TransformBlock(inputBuffer: ciphertext.Array, inputOffset: ciphertext.Offset + CONTEXT_BUFFER_LENGTH, inputCount: fullBlockLength, outputBuffer: outputSegment.Value.Array, outputOffset: outputSegment.Value.Offset);
finalBlock = aesDecryptor.TransformFinalBlock(ciphertext.Array, ciphertext.Offset + CONTEXT_BUFFER_LENGTH + fullBlockLength, cipherLength - fullBlockLength);
Utils.BlockCopy(finalBlock, 0, outputSegment.Value.Array, outputSegment.Value.Offset + fullBlockTransformed, finalBlock.Length);
outputSegment = new ArraySegment<byte>?(new ArraySegment<byte>(outputSegment.Value.Array, outputSegment.Value.Offset, fullBlockTransformed + finalBlock.Length));
}// using aesDecryptor
}// using aes
}
finally
{
EtM_CBC.ClearKeyMaterial();
if (finalBlock != null) Array.Clear(finalBlock, 0, finalBlock.Length);
}
}// Decrypt()
public static void Encrypt(byte[] masterKey, ArraySegment<byte> plaintext, byte[] output, int outputOffset, ArraySegment<byte>? salt = null, uint counter = 1)
{
int fullBlockLength = plaintext.Count & (-Cipher.AesConstants.AES_BLOCK_SIZE);
int finalBlockLength = plaintext.Count % Cipher.AesConstants.AES_BLOCK_SIZE;
int paddingLength = Cipher.AesConstants.AES_BLOCK_SIZE - finalBlockLength;
int ciphertextLength = CONTEXT_BUFFER_LENGTH + plaintext.Count + paddingLength + MAC_LENGTH;
if (output.Length - outputOffset < ciphertextLength) throw new ArgumentOutOfRangeException(nameof(output), $"'{nameof(output)}' array segment is not big enough for the ciphertext");
try
{
var iv = _iv.Value;
var contextBuffer = _contextBuffer.Value;
var encKey = _encKey.Value;
var macKey = _macKey.Value;
var sessionKey = _sessionKey.Value;
using (var aes = _aesFactory())
{
EtM_CBC.ValidateAes(aes);
_cryptoRandom.NextBytes(contextBuffer, 0, CONTEXT_BUFFER_LENGTH);
Utils.BlockCopy(contextBuffer, CONTEXT_TWEAK_LENGTH, iv, 0, AES_IV_LENGTH);
Kdf.SP800_108_Ctr.DeriveKey(hmacFactory: _hmacFactory, key: masterKey, label: salt, context: contextBuffer.AsArraySegment(), derivedOutput: sessionKey.AsArraySegment(), counter: counter);
Utils.BlockCopy(sessionKey, 0, macKey, 0, MAC_KEY_LENGTH);
Utils.BlockCopy(sessionKey, MAC_KEY_LENGTH, encKey, 0, ENC_KEY_LENGTH);
Utils.BlockCopy(contextBuffer, 0, output, outputOffset, CONTEXT_BUFFER_LENGTH);
using (var aesEncryptor = aes.CreateEncryptor(encKey, iv))
{
if (fullBlockLength > 0)
aesEncryptor.TransformBlock(inputBuffer: plaintext.Array, inputOffset: plaintext.Offset, inputCount: fullBlockLength, outputBuffer: output, outputOffset: outputOffset + CONTEXT_BUFFER_LENGTH);
var finalBlockBuffer = aesEncryptor.TransformFinalBlock(inputBuffer: plaintext.Array, inputOffset: plaintext.Offset + fullBlockLength, inputCount: finalBlockLength);
Utils.BlockCopy(finalBlockBuffer, 0, output, outputOffset + CONTEXT_BUFFER_LENGTH + fullBlockLength, finalBlockBuffer.Length);
}// using aesEncryptor
}// using aes
using (var hmac = _hmacFactory())
{
hmac.Key = macKey;
hmac.TransformBlock(output, outputOffset + CONTEXT_TWEAK_LENGTH, AES_IV_LENGTH + plaintext.Count + paddingLength, null, 0);
hmac.TransformFinalBlock(output, 0, 0);
var fullmac = hmac.HashInner;
Utils.BlockCopy(fullmac, 0, output, outputOffset + ciphertextLength - MAC_LENGTH, MAC_LENGTH);
}// using hmac
}
finally { EtM_CBC.ClearKeyMaterial(); }
}// Encrypt()
}// Decrypt()
public static bool Authenticate(byte[] masterKey, ArraySegment<byte> ciphertext, ArraySegment<byte>? salt = null, uint counter = 1)
{
int cipherLength = ciphertext.Count - CONTEXT_BUFFER_LENGTH - MAC_LENGTH;
if (cipherLength < Cipher.AesConstants.AES_BLOCK_SIZE) return false;
try
{
var macKey = _macKey.Value;
var sessionKey = _sessionKey.Value;
Kdf.SP800_108_Ctr.DeriveKey(hmacFactory: _hmacFactory, key: masterKey, label: salt, context: new ArraySegment<byte>(ciphertext.Array, ciphertext.Offset, CONTEXT_BUFFER_LENGTH), derivedOutput: sessionKey.AsArraySegment(), counter: counter);
Utils.BlockCopy(sessionKey, 0, macKey, 0, MAC_KEY_LENGTH);
using (var hmac = _hmacFactory())
{
hmac.Key = macKey;
hmac.TransformBlock(ciphertext.Array, ciphertext.Offset + CONTEXT_TWEAK_LENGTH, AES_IV_LENGTH + cipherLength, null, 0);
hmac.TransformFinalBlock(ciphertext.Array, 0, 0);
var fullmacActual = hmac.HashInner;
if (!Utils.ConstantTimeEqual(fullmacActual, 0, ciphertext.Array, ciphertext.Offset + ciphertext.Count - MAC_LENGTH, MAC_LENGTH)) return false;
}// using hmac
return true;
}
finally { EtM_CBC.ClearKeyMaterial(); }
}// Authenticate()
