/// <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>
/// Get Hmac-Sha1-Aes Checksum
/// </summary>
/// <param name="key">the key</param>
/// <param name="input">input data</param>
/// <param name="usage">usage number</param>
/// <param name="aesKeyType">aes key type which decides key size</param>
/// <returns>the calculated checksum</returns>
public static byte[] GetMic(
byte[] key,
byte[] input,
int usage,
AesKeyType aesKeyType)
{
// make the kc key from aes key generation
byte[] kcKey = AesKey.MakeDerivedKey(
key, usage, DerivedKeyType.Kc, aesKeyType);
// get mic from kc key and input
byte[] hash = CryptoUtility.ComputeHmacSha1(kcKey, input);
return(ArrayUtility.SubArray(hash, 0, ConstValue.HMAC_HASH_OUTPUT_SIZE));
}
/// <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));
}
