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//------------------------------------------------------------------------------
// <copyright file="SqlAeadAes256CbcHmac256Algorithm.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
// <owner current="true" primary="true">balnee</owner>
// <owner current="true" primary="false">krishnib</owner>
//------------------------------------------------------------------------------
namespace System.Data.SqlClient
{
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Diagnostics;
using System.IO;
using System.Runtime.CompilerServices;
using System.Security.Cryptography;
/// <summary>
/// This class implements authenticated encryption algorithm with associated data as described in
/// http://tools.ietf.org/html/draft-mcgrew-aead-aes-cbc-hmac-sha2-05. More specifically this implements
/// AEAD_AES_256_CBC_HMAC_SHA256 algorithm.
/// </summary>
internal class SqlAeadAes256CbcHmac256Algorithm : SqlClientEncryptionAlgorithm
{
/// <summary>
/// Algorithm Name
/// </summary>
internal const string AlgorithmName = @"AEAD_AES_256_CBC_HMAC_SHA256";
/// <summary>
/// Key size in bytes
/// </summary>
private const int _KeySizeInBytes = SqlAeadAes256CbcHmac256EncryptionKey.KeySize / 8;
/// <summary>
/// Block size in bytes. AES uses 16 byte blocks.
/// </summary>
private const int _BlockSizeInBytes = 16;
/// <summary>
/// Minimum Length of cipherText without authentication tag. This value is 1 (version byte) + 16 (IV) + 16 (minimum of 1 block of cipher Text)
/// </summary>
private const int _MinimumCipherTextLengthInBytesNoAuthenticationTag = sizeof(byte) + _BlockSizeInBytes + _BlockSizeInBytes;
/// <summary>
/// Minimum Length of cipherText. This value is 1 (version byte) + 32 (authentication tag) + 16 (IV) + 16 (minimum of 1 block of cipher Text)
/// </summary>
private const int _MinimumCipherTextLengthInBytesWithAuthenticationTag = _MinimumCipherTextLengthInBytesNoAuthenticationTag + _KeySizeInBytes;
/// <summary>
/// Cipher Mode. For this algorithm, we only use CBC mode.
/// </summary>
private const CipherMode _cipherMode = CipherMode.CBC;
/// <summary>
/// Padding mode. This algorithm uses PKCS7.
/// </summary>
private const PaddingMode _paddingMode = PaddingMode.PKCS7;
/// <summary>
/// Variable indicating whether this algorithm should work in Deterministic mode or Randomized mode.
/// For deterministic encryption, we derive an IV from the plaintext data.
/// For randomized encryption, we generate a cryptographically random IV.
/// </summary>
private readonly bool _isDeterministic;
/// <summary>
/// Algorithm Version.
/// </summary>
private readonly byte _algorithmVersion;
/// <summary>
/// Column Encryption Key. This has a root key and three derived keys.
/// </summary>
private readonly SqlAeadAes256CbcHmac256EncryptionKey _columnEncryptionKey;
/// <summary>
/// The pool of crypto providers to use for encrypt/decrypt operations.
/// </summary>
private readonly ConcurrentQueue<AesCryptoServiceProvider> _cryptoProviderPool;
/// <summary>
/// Byte array with algorithm version used for authentication tag computation.
/// </summary>
private static readonly byte[] _version = new byte[] {0x01};
/// <summary>
/// Byte array with algorithm version size used for authentication tag computation.
/// </summary>
private static readonly byte[] _versionSize = new byte[] {sizeof(byte)};
/// <summary>
/// Initializes a new instance of SqlAeadAes256CbcHmac256Algorithm algorithm with a given key and encryption type
/// </summary>
/// <param name="encryptionKey">
/// Root encryption key from which three other keys will be derived
/// </param>
/// <param name="encryptionType">Encryption Type, accepted values are Deterministic and Randomized.
/// For Deterministic encryption, a synthetic IV will be genenrated during encryption
/// For Randomized encryption, a random IV will be generated during encryption.
/// </param>
/// <param name="algorithmVersion">
/// Algorithm version
/// </param>
internal SqlAeadAes256CbcHmac256Algorithm(SqlAeadAes256CbcHmac256EncryptionKey encryptionKey, SqlClientEncryptionType encryptionType, byte algorithmVersion) {
_columnEncryptionKey = encryptionKey;
_algorithmVersion = algorithmVersion;
_version[0] = algorithmVersion;
Debug.Assert (null != encryptionKey, "Null encryption key detected in AeadAes256CbcHmac256 algorithm");
Debug.Assert (0x01 == algorithmVersion, "Unknown algorithm version passed to AeadAes256CbcHmac256");
// Validate encryption type for this algorithm
// This algorithm can only provide randomized or deterministic encryption types.
if (encryptionType == SqlClientEncryptionType.Deterministic) {
_isDeterministic = true;
}
else {
Debug.Assert (SqlClientEncryptionType.Randomized == encryptionType, "Invalid Encryption Type detected in SqlAeadAes256CbcHmac256Algorithm, this should've been caught in factory class");
}
_cryptoProviderPool = new ConcurrentQueue<AesCryptoServiceProvider>();
}
/// <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.
/// 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>
/// <returns>Returns the ciphertext corresponding to the plaintext.</returns>
internal override byte[] EncryptData(byte[] plainText) {
return EncryptData(plainText, hasAuthenticationTag: true);
}
/// <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;
}
/// <summary>
/// Decryption steps
/// 1. Validate version byte
/// 2. Validate Authentication tag
/// 3. Decrypt the message
/// </summary>
/// <param name="cipherText"></param>
/// <returns></returns>
internal override byte[] DecryptData(byte[] cipherText) {
return DecryptData(cipherText, hasAuthenticationTag: true);
}
/// <summary>
/// Decryption steps
/// 1. Validate version byte
/// 2. (optional) Validate Authentication tag
/// 3. Decrypt the message
/// </summary>
/// <param name="cipherText"></param>
/// <param name="hasAuthenticationTag"></param>
/// <returns></returns>
protected byte[] DecryptData(byte[] cipherText, bool hasAuthenticationTag) {
Debug.Assert(cipherText != null);
byte[] iv = new byte[_BlockSizeInBytes];
int minimumCipherTextLength = hasAuthenticationTag ? _MinimumCipherTextLengthInBytesWithAuthenticationTag : _MinimumCipherTextLengthInBytesNoAuthenticationTag;
if (cipherText.Length < minimumCipherTextLength) {
throw SQL.InvalidCipherTextSize(cipherText.Length, minimumCipherTextLength);
}
// Validate the version byte
int startIndex = 0;
if (cipherText[startIndex] != _algorithmVersion) {
// Cipher text was computed with a different algorithm version than this.
throw SQL.InvalidAlgorithmVersion(cipherText[startIndex], _algorithmVersion);
}
startIndex += 1;
int authenticationTagOffset = 0;
// Read authentication tag
if (hasAuthenticationTag) {
authenticationTagOffset = startIndex;
startIndex += _KeySizeInBytes; // authentication tag size is _KeySizeInBytes
}
// Read cell IV
Buffer.BlockCopy(cipherText, startIndex, iv, 0, iv.Length);
startIndex += iv.Length;
// Read encrypted text
int cipherTextOffset = startIndex;
int cipherTextCount = cipherText.Length - startIndex;
if (hasAuthenticationTag) {
// Compute authentication tag
byte[] authenticationTag = PrepareAuthenticationTag(iv, cipherText, cipherTextOffset, cipherTextCount);
if (!SqlSecurityUtility.CompareBytes(authenticationTag, cipherText, authenticationTagOffset, authenticationTag.Length)) {
// Potentially tampered data, throw an exception
throw SQL.InvalidAuthenticationTag();
}
}
// Decrypt the text and return
return DecryptData(iv, cipherText, cipherTextOffset, cipherTextCount);
}
/// <summary>
/// Decrypts plain text data using AES in CBC mode
/// </summary>
/// <param name="plainText"> cipher text data to be decrypted</param>
/// <param name="iv">IV to be used for decryption</param>
/// <returns>Returns decrypted plain text data</returns>
private byte[] DecryptData(byte[] iv, byte[] cipherText, int offset, int count) {
Debug.Assert((iv != null) && (cipherText != null));
Debug.Assert (offset > -1 && count > -1);
Debug.Assert ((count+offset) <= cipherText.Length);
byte[] plainText;
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;
// Create the streams used for decryption.
using (MemoryStream msDecrypt = new MemoryStream()) {
// Create an encryptor to perform the stream transform.
using (ICryptoTransform decryptor = aesAlg.CreateDecryptor()) {
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Write)) {
// Decrypt the secret message and get the plain text data
csDecrypt.Write(cipherText, offset, count);
csDecrypt.FlushFinalBlock();
plainText = msDecrypt.ToArray();
}
}
}
}
finally {
// Return the provider to the pool.
_cryptoProviderPool.Enqueue(aesAlg);
}
return plainText;
}
/// <summary>
/// Prepares an authentication tag.
/// Authentication Tag = HMAC_SHA-2-256(mac_key, versionbyte + cell_iv + cell_ciphertext + versionbyte_length)
/// </summary>
/// <param name="cipherText"></param>
/// <returns></returns>
private byte[] PrepareAuthenticationTag(byte[] iv, byte[] cipherText, int offset, int length) {
Debug.Assert(cipherText != null);
byte[] computedHash;
byte[] authenticationTag = new byte[_KeySizeInBytes];
// Raw Tag Length:
// 1 for the version byte
// 1 block for IV (16 bytes)
// cipherText.Length
// 1 byte for version byte length
using (HMACSHA256 hmac = new HMACSHA256(_columnEncryptionKey.MACKey)) {
int retVal = 0;
retVal = hmac.TransformBlock(_version, 0, _version.Length, _version, 0);
Debug.Assert(retVal == _version.Length);
retVal = hmac.TransformBlock(iv, 0, iv.Length, iv, 0);
Debug.Assert(retVal == iv.Length);
retVal = hmac.TransformBlock(cipherText, offset, length, cipherText, offset);
Debug.Assert(retVal == length);
hmac.TransformFinalBlock(_versionSize, 0, _versionSize.Length);
computedHash = hmac.Hash;
}
Debug.Assert (computedHash.Length >= authenticationTag.Length);
Buffer.BlockCopy (computedHash, 0, authenticationTag, 0, authenticationTag.Length);
return authenticationTag;
}
}
}
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