/// <summary>
/// Derives all the required keys from the given root key
/// </summary>
/// <param name="rootKey">Root key used to derive all the required derived keys</param>
internal SqlAeadAes256CbcHmac256EncryptionKey(byte[] rootKey, string algorithmName) : base(rootKey)
{
_algorithmName = algorithmName;
int keySizeInBytes = KeySize / 8;
// Key validation
if (rootKey.Length != keySizeInBytes)
{
throw SQL.InvalidKeySize(_algorithmName,
rootKey.Length,
keySizeInBytes);
}
// Derive keys from the root key
//
// Derive encryption key
string encryptionKeySalt = string.Format(_encryptionKeySaltFormat,
_algorithmName,
KeySize);
byte[] buff1 = new byte[keySizeInBytes];
SqlSecurityUtility.GetHMACWithSHA256(Encoding.Unicode.GetBytes(encryptionKeySalt), RootKey, buff1);
_encryptionKey = new SqlClientSymmetricKey(buff1);
// Derive mac key
string macKeySalt = string.Format(_macKeySaltFormat, _algorithmName, KeySize);
byte[] buff2 = new byte[keySizeInBytes];
SqlSecurityUtility.GetHMACWithSHA256(Encoding.Unicode.GetBytes(macKeySalt), RootKey, buff2);
_macKey = new SqlClientSymmetricKey(buff2);
// Derive iv key
string ivKeySalt = string.Format(_ivKeySaltFormat, _algorithmName, KeySize);
byte[] buff3 = new byte[keySizeInBytes];
SqlSecurityUtility.GetHMACWithSHA256(Encoding.Unicode.GetBytes(ivKeySalt), RootKey, buff3);
_ivKey = new SqlClientSymmetricKey(buff3);
}
/// <summary>
/// Encryption Algorithm
/// cell_iv = HMAC_SHA-2-256(iv_key, cell_data) truncated to 128 bits
/// cell_ciphertext = AES-CBC-256(enc_key, cell_iv, cell_data) with PKCS7 padding.
/// (optional) cell_tag = HMAC_SHA-2-256(mac_key, versionbyte + cell_iv + cell_ciphertext + versionbyte_length)
/// cell_blob = versionbyte + [cell_tag] + cell_iv + cell_ciphertext
/// </summary>
/// <param name="plainText">Plaintext data to be encrypted</param>
/// <param name="hasAuthenticationTag">Does the algorithm require authentication tag.</param>
/// <returns>Returns the ciphertext corresponding to the plaintext.</returns>
protected byte[] EncryptData(byte[] plainText, bool hasAuthenticationTag)
{
// Empty values get encrypted and decrypted properly for both Deterministic and Randomized encryptions.
Debug.Assert(plainText != null);
byte[] iv = new byte[_BlockSizeInBytes];
// Prepare IV
// Should be 1 single block (16 bytes)
if (_isDeterministic)
{
SqlSecurityUtility.GetHMACWithSHA256(plainText, _columnEncryptionKey.IVKey, iv);
}
else
{
SqlSecurityUtility.GenerateRandomBytes(iv);
}
int numBlocks = plainText.Length / _BlockSizeInBytes + 1;
// Final blob we return = version + HMAC + iv + cipherText
const int hmacStartIndex = 1;
int authenticationTagLen = hasAuthenticationTag ? _KeySizeInBytes : 0;
int ivStartIndex = hmacStartIndex + authenticationTagLen;
int cipherStartIndex = ivStartIndex + _BlockSizeInBytes; // this is where hmac starts.
// Output buffer size = size of VersionByte + Authentication Tag + IV + cipher Text blocks.
int outputBufSize = sizeof(byte) + authenticationTagLen + iv.Length + (numBlocks * _BlockSizeInBytes);
byte[] outBuffer = new byte[outputBufSize];
// Store the version and IV rightaway
outBuffer[0] = _algorithmVersion;
Buffer.BlockCopy(iv, 0, outBuffer, ivStartIndex, iv.Length);
AesCryptoServiceProvider aesAlg;
// Try to get a provider from the pool.
// If no provider is available, create a new one.
if (!_cryptoProviderPool.TryDequeue(out aesAlg))
{
aesAlg = new AesCryptoServiceProvider();
try {
// Set various algorithm properties
aesAlg.Key = _columnEncryptionKey.EncryptionKey;
aesAlg.Mode = _cipherMode;
aesAlg.Padding = _paddingMode;
}
catch (Exception) {
if (aesAlg != null)
{
aesAlg.Dispose();
}
throw;
}
}
try {
// Always set the IV since it changes from cell to cell.
aesAlg.IV = iv;
// Compute CipherText and authentication tag in a single pass
using (ICryptoTransform encryptor = aesAlg.CreateEncryptor()) {
Debug.Assert(encryptor.CanTransformMultipleBlocks, "AES Encryptor can transform multiple blocks");
int count = 0;
int cipherIndex = cipherStartIndex; // this is where cipherText starts
if (numBlocks > 1)
{
count = (numBlocks - 1) * _BlockSizeInBytes;
cipherIndex += encryptor.TransformBlock(plainText, 0, count, outBuffer, cipherIndex);
}
byte[] buffTmp = encryptor.TransformFinalBlock(plainText, count, plainText.Length - count); // done encrypting
Buffer.BlockCopy(buffTmp, 0, outBuffer, cipherIndex, buffTmp.Length);
cipherIndex += buffTmp.Length;
}
if (hasAuthenticationTag)
{
using (HMACSHA256 hmac = new HMACSHA256(_columnEncryptionKey.MACKey)) {
Debug.Assert(hmac.CanTransformMultipleBlocks, "HMAC can't transform multiple blocks");
hmac.TransformBlock(_version, 0, _version.Length, _version, 0);
hmac.TransformBlock(iv, 0, iv.Length, iv, 0);
// Compute HMAC on final block
hmac.TransformBlock(outBuffer, cipherStartIndex, numBlocks * _BlockSizeInBytes, outBuffer, cipherStartIndex);
hmac.TransformFinalBlock(_versionSize, 0, _versionSize.Length);
byte[] hash = hmac.Hash;
Debug.Assert(hash.Length >= authenticationTagLen, "Unexpected hash size");
Buffer.BlockCopy(hash, 0, outBuffer, hmacStartIndex, authenticationTagLen);
}
}
}
finally {
// Return the provider to the pool.
_cryptoProviderPool.Enqueue(aesAlg);
}
return(outBuffer);
}
