private static byte[] PRF(EncryptionType type, byte[] protocolKey, byte[] truncated)
{
byte[] prf = Encoding.UTF8.GetBytes("prf");
switch (type)
{
case EncryptionType.AES256_CTS_HMAC_SHA1_96:
{
byte[] temp = AesKey.DK(protocolKey, prf, AesKeyType.Aes256BitsKey);
byte[] initialVector = new byte[ConstValue.AES_BLOCK_SIZE];
CipherTextStealingMode aesCtsCrypto = CryptoUtility.CreateAesCtsCrypto(temp, initialVector);
byte[] encryptedData = aesCtsCrypto.EncryptFinal(truncated, 0, truncated.Length);
return(encryptedData);
}
case EncryptionType.AES128_CTS_HMAC_SHA1_96:
{
byte[] temp = AesKey.DK(protocolKey, prf, AesKeyType.Aes128BitsKey);
break;
}
default:
throw new NotSupportedException("Encryption type not support");
}
throw new NotImplementedException();
}
/// <summary>
/// Decrypt in aes128-cts-hmac-sha1-96 or aes256-cts-hmac-sha1-96
/// </summary>
/// <param name="key">key data</param>
/// <param name="cipher">cipher data to be decrypted</param>
/// <param name="usage">key usage number</param>
/// <param name="aesKeyType">aes key type (128bit/256bit)</param>
/// <param name="getToBeSignedDateCallback">
/// A callback to get to-be-signed data.
/// The method will use decrypted data directly if this parameter is null.
/// </param>
/// <returns>the decrypted data</returns>
public static byte[] Decrypt(
byte[] key,
byte[] cipher,
int usage,
AesKeyType aesKeyType,
GetToBeSignedDataFunc getToBeSignedDateCallback)
{
// check inputs
if (null == key)
{
throw new ArgumentNullException("key");
}
if (null == cipher)
{
throw new ArgumentNullException("cipher");
}
// the cipher has two parts: encrypted(confounder + plain) + hmac
byte[] encryptedData = ArrayUtility.SubArray <byte>(
cipher, 0, cipher.Length - ConstValue.HMAC_HASH_OUTPUT_SIZE);
byte[] hmacData = ArrayUtility.SubArray <byte>(
cipher, cipher.Length - ConstValue.HMAC_HASH_OUTPUT_SIZE);
// use ke key (the encryption key) to decrypt
byte[] ke = AesKey.MakeDerivedKey(key, usage, DerivedKeyType.Ke, aesKeyType);
byte[] initialVector = new byte[ConstValue.AES_BLOCK_SIZE];
CipherTextStealingMode aesCtsCrypto = CryptoUtility.CreateAesCtsCrypto(ke, initialVector);
byte[] decryptedData = aesCtsCrypto.DecryptFinal(encryptedData, 0, encryptedData.Length);
byte[] toBeSignedData;
if (getToBeSignedDateCallback != null)
{
toBeSignedData = getToBeSignedDateCallback(decryptedData);
}
else
{
toBeSignedData = decryptedData;
}
// use ki key (the integrity key) to verify hmac data
byte[] ki = AesKey.MakeDerivedKey(key, usage, DerivedKeyType.Ki, aesKeyType);
byte[] expectedHmacData = CryptoUtility.ComputeHmacSha1(ki, toBeSignedData);
expectedHmacData = ArrayUtility.SubArray <byte>(expectedHmacData, 0, ConstValue.HMAC_HASH_OUTPUT_SIZE);
if (!ArrayUtility.CompareArrays <byte>(hmacData, expectedHmacData))
{
throw new FormatException(
"Decryption: failed integrity check in hmac checksum.");
}
// remove confounder data
decryptedData = ArrayUtility.SubArray <byte>(decryptedData, ConstValue.AES_BLOCK_SIZE,
decryptedData.Length - ConstValue.AES_BLOCK_SIZE);
return(decryptedData);
}
/// <summary>
/// Encrypt in aes128-cts-hmac-sha1-96 or aes256-cts-hmac-sha1-96
/// </summary>
/// <param name="key">key data</param>
/// <param name="plain">plain data to be encrypted</param>
/// <param name="usage">key usage number</param>
/// <param name="aesKeyType">aes key type (128bit/256bit)</param>
/// <param name="getToBeSignedDateCallback">
/// A callback to get to-be-signed data.
/// The method will use plain-text data directly if this parameter is null.
/// </param>
/// <returns>the encrypted data</returns>
public static byte[] Encrypt(
byte[] key,
byte[] plain,
int usage,
AesKeyType aesKeyType,
GetToBeSignedDataFunc getToBeSignedDateCallback)
{
// check inputs
if (null == key)
{
throw new ArgumentNullException("key");
}
if (null == plain)
{
throw new ArgumentNullException("plain");
}
// add confounder data
byte[] plainData = ArrayUtility.ConcatenateArrays(
CryptoUtility.CreateConfounder(ConstValue.AES_BLOCK_SIZE),
plain);
// use ke key (the encryption key) to encrypt the plain data
byte[] ke = AesKey.MakeDerivedKey(key, usage, DerivedKeyType.Ke, aesKeyType);
byte[] initialVector = new byte[ConstValue.AES_BLOCK_SIZE];
CipherTextStealingMode aesCtsCrypto = CryptoUtility.CreateAesCtsCrypto(ke, initialVector);
byte[] encryptedData = aesCtsCrypto.EncryptFinal(plainData, 0, plainData.Length);
byte[] toBeSignedData;
if (getToBeSignedDateCallback != null)
{
toBeSignedData = getToBeSignedDateCallback(plainData);
}
else
{
toBeSignedData = plainData;
}
// use ki key (the integrity key) to generate checksum
byte[] ki = AesKey.MakeDerivedKey(key, usage, DerivedKeyType.Ki, aesKeyType);
byte[] hmacData = CryptoUtility.ComputeHmacSha1(ki, toBeSignedData);
hmacData = ArrayUtility.SubArray <byte>(hmacData, 0, ConstValue.HMAC_HASH_OUTPUT_SIZE);
// result: encryptedData + hmacData
return(ArrayUtility.ConcatenateArrays(encryptedData, hmacData));
}
/// <summary>
/// DR is the random-octet generation function described in RFC 3961
/// [RFC 3961 section 5.1 A Key Derivation Function]
/// </summary>
/// <param name="baseKey">the base key which is to be derived from</param>
/// <param name="wellKnownConstant">the "well-known constant"</param>
/// <param name="aesKeyType">AES key type which decides key size</param>
/// <returns>the pseudorandom octets</returns>
private static byte[] DR(
byte[] baseKey,
byte[] wellKnownConstant,
AesKeyType aesKeyType)
{
// to be encrypted data
byte[] toBeEncrypted = new byte[wellKnownConstant.Length];
wellKnownConstant.CopyTo(toBeEncrypted, 0);
// n-fold the "well-known constant" if needed
if (wellKnownConstant.Length != ConstValue.AES_BLOCK_SIZE)
{
toBeEncrypted = NFold(wellKnownConstant, ConstValue.AES_BLOCK_SIZE * ConstValue.BYTE_SIZE);
}
// AES key size
uint aesKeySize = (uint)aesKeyType / ConstValue.BYTE_SIZE;
// initialize key array
byte[] rawkey = new byte[aesKeySize];
// count means the total number of bytes has been copy to the rawkey.
// length means how length of bytes should be copy to the rawkey array.
uint count = 0;
uint length = 0;
// The initialCipherVector should be all zeros.
byte[] initialCipherVector = new byte[ConstValue.AES_BLOCK_SIZE];
// AES-CTS encryptor
CipherTextStealingMode aesCtsCrypto = CryptoUtility.CreateAesCtsCrypto(baseKey, initialCipherVector);
while (count < aesKeySize)
{
byte[] cipherBlock = aesCtsCrypto.EncryptFinal(toBeEncrypted, 0, toBeEncrypted.Length);
length = (aesKeySize - count <= cipherBlock.Length ? (aesKeySize - count) : Convert.ToUInt32(cipherBlock.Length));
Array.Copy(cipherBlock, 0, rawkey, count, length);
count += length;
toBeEncrypted = cipherBlock;
}
return(rawkey);
}
