public byte[] Decrypt(byte[] aad, byte[] cek, byte[] iv, byte[] cipherText, byte[] authTag)
{
Ensure.BitSize(cek, keyLength, string.Format("AES-CBC with HMAC algorithm expected key of size {0} bits, but was given {1} bits", keyLength, cek.Length * 8L));
byte[] hmacKey = Arrays.FirstHalf(cek);
byte[] aesKey = Arrays.SecondHalf(cek);
// Check MAC
byte[] expectedAuthTag = ComputeAuthTag(aad, iv, cipherText, hmacKey);
if (!Arrays.ConstantTimeEquals(expectedAuthTag, authTag))
{
throw new IntegrityException("Authentication tag do not match.");
}
try
{
using (Aes aes = Aes.Create())
{
aes.Key = aesKey;
aes.IV = iv;
using (MemoryStream ms = new MemoryStream())
{
using (ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV))
{
using (CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Write))
{
cs.Write(cipherText, 0, cipherText.Length);
cs.FlushFinalBlock();
return(ms.ToArray());
}
}
}
}
}
catch (CryptographicException e)
{
throw new EncryptionException("Unable to decrypt content", e);
}
}
public byte[][] Encrypt(byte[] aad, byte[] plainText, byte[] cek)
{
Ensure.BitSize(cek, keyLength, string.Format("AES-CBC with HMAC algorithm expected key of size {0} bits, but was given {1} bits", keyLength, cek.Length * 8L));
byte[] hmacKey = Arrays.FirstHalf(cek);
byte[] aesKey = Arrays.SecondHalf(cek);
byte[] iv = Arrays.Random();
byte[] cipherText;
try
{
using (Aes aes = Aes.Create())
{
aes.Key = aesKey;
aes.IV = iv;
using (MemoryStream ms = new MemoryStream())
{
using (ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV))
{
using (CryptoStream encrypt = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
{
encrypt.Write(plainText, 0, plainText.Length);
encrypt.FlushFinalBlock();
cipherText = ms.ToArray();
}
}
}
}
}
catch (CryptographicException e)
{
throw new EncryptionException("Unable to encrypt content.", e);
}
byte[] authTag = ComputeAuthTag(aad, iv, cipherText, hmacKey);
return(new[] { iv, cipherText, authTag });
}
public static byte[] Unwrap(byte[] encryptedCek, byte[] kek)
{
Ensure.MinBitSize(encryptedCek, 128, "AesKeyWrap.Unwrap() expects content length not less than 128 bits, but was {0}", encryptedCek.Length * 8);
Ensure.Divisible(encryptedCek.Length, 8, "AesKeyWrap.Unwrap() expects content length to be divisable by 8, but was given a content of {0} bit size.", encryptedCek.Length * 8);
// 1) Initialize variables
byte[][] c = Arrays.Slice(encryptedCek, 8);
byte[] a = c[0]; // Set A = C[0]
byte[][] r = new byte[c.Length - 1][];
for (int i = 1; i < c.Length; i++) // For i = 1 to n
{
r[i - 1] = c[i]; // R[i] = C[i]
}
long n = r.Length;
// 2) Calculate intermediate values
for (long j = 5; j >= 0; j--) // For j = 5 to 0
{
for (long i = n - 1; i >= 0; i--) // For i = n to 1
{
long t = n * j + i + 1;
a = Arrays.Xor(a, t);
byte[] B = AesDec(kek, Arrays.Concat(a, r[i])); // B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
a = Arrays.FirstHalf(B); // A = MSB(64, B)
r[i] = Arrays.SecondHalf(B); // R[i] = LSB(64, B)
}
}
// 3) Output the results
if (!Arrays.ConstantTimeEquals(DefaultIV, a)) // If A is an appropriate initial value
{
throw new IntegrityException("AesKeyWrap integrity check failed.");
}
// For i = 1 to n
return(Arrays.Concat(r)); // P[i] = R[i]
}
public byte[] Decrypt(byte[] aad, byte[] cek, byte[] iv, byte[] cipherText, byte[] authTag)
{
byte[] array;
Ensure.BitSize(cek, this.keyLength, string.Format("AES-CBC with HMAC algorithm expected key of size {0} bits, but was given {1} bits", this.keyLength, (int)cek.Length * 8), new object[0]);
byte[] numArray = Arrays.FirstHalf(cek);
byte[] numArray1 = Arrays.SecondHalf(cek);
if (!Arrays.ConstantTimeEquals(this.ComputeAuthTag(aad, iv, cipherText, numArray), authTag))
{
throw new IntegrityException("Authentication tag do not match.");
}
try
{
using (Aes ae = Aes.Create())
{
ae.Key = numArray1;
ae.IV = iv;
using (MemoryStream memoryStream = new MemoryStream())
{
using (ICryptoTransform cryptoTransform = ae.CreateDecryptor(ae.Key, ae.IV))
{
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, cryptoTransform, CryptoStreamMode.Write))
{
cryptoStream.Write(cipherText, 0, (int)cipherText.Length);
cryptoStream.FlushFinalBlock();
array = memoryStream.ToArray();
}
}
}
}
}
catch (CryptographicException cryptographicException)
{
throw new EncryptionException("Unable to decrypt content", cryptographicException);
}
return(array);
}
private byte[] ComputeAuthTag(byte[] aad, byte[] iv, byte[] cipherText, byte[] hmacKey)
{
byte[] bytes = Arrays.LongToBytes((long)((int)aad.Length * 8));
byte[] numArray = Arrays.Concat(new byte[][] { aad, iv, cipherText, bytes });
return(Arrays.FirstHalf(this.hashAlgorithm.Sign(numArray, hmacKey)));
}