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//------------------------------------------------------------------------------
// <copyright file="SqlColumnEncryptionCspProvider.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.Text;
using System.Data.Common;
using System.Diagnostics;
using System.Globalization;
using System.Security;
using System.Security.Cryptography;
using Microsoft.Win32;
/// <summary>
/// Provides implementation similar to certificate store provider.
/// A CEK encrypted with certificate store provider should be decryptable by this provider and vice versa.
///
/// Envolope Format for the encrypted column encryption key
/// version + keyPathLength + ciphertextLength + keyPath + ciphertext + signature
/// version: A single byte indicating the format version.
/// keyPathLength: Length of the keyPath.
/// ciphertextLength: ciphertext length
/// keyPath: keyPath used to encrypt the column encryption key. This is only used for troubleshooting purposes and is not verified during decryption.
/// ciphertext: Encrypted column encryption key
/// signature: Signature of the entire byte array. Signature is validated before decrypting the column encryption key.
/// </summary>
public class SqlColumnEncryptionCspProvider : SqlColumnEncryptionKeyStoreProvider
{
/// <summary>
/// Name for the CSP key store provider.
/// </summary>
public const string ProviderName = @"MSSQL_CSP_PROVIDER";
/// <summary>
/// RSA_OAEP is the only algorithm supported for encrypting/decrypting column encryption keys using this provider.
/// For now, we are keeping all the providers in sync.
/// </summary>
private const string RSAEncryptionAlgorithmWithOAEP = @"RSA_OAEP";
/// <summary>
/// Hashing algoirthm used for signing
/// </summary>
private const string HashingAlgorithm = @"SHA256";
/// <summary>
/// Algorithm version
/// </summary>
private readonly byte[] _version = new byte[] { 0x01 };
/// <summary>
/// This function uses the asymmetric key specified by the key path
/// and decrypts an encrypted CEK with RSA encryption algorithm.
/// </summary>
/// <param name="masterKeyPath">Complete path of an asymmetric key in CSP</param>
/// <param name="encryptionAlgorithm">Asymmetric Key Encryption Algorithm</param>
/// <param name="encryptedColumnEncryptionKey">Encrypted Column Encryption Key</param>
/// <returns>Plain text column encryption key</returns>
public override byte[] DecryptColumnEncryptionKey(string masterKeyPath, string encryptionAlgorithm, byte[] encryptedColumnEncryptionKey)
{
// Validate the input parameters
ValidateNonEmptyCSPKeyPath(masterKeyPath, isSystemOp: true);
if (null == encryptedColumnEncryptionKey)
{
throw SQL.NullEncryptedColumnEncryptionKey();
}
if (0 == encryptedColumnEncryptionKey.Length)
{
throw SQL.EmptyEncryptedColumnEncryptionKey();
}
// Validate encryptionAlgorithm
ValidateEncryptionAlgorithm(encryptionAlgorithm, isSystemOp: true);
// Create RSA Provider with the given CSP name and key name
RSACryptoServiceProvider rsaProvider = CreateRSACryptoProvider(masterKeyPath, isSystemOp: true);
// Validate whether the key is RSA one or not and then get the key size
int keySizeInBytes = GetKeySize(rsaProvider);
// Validate and decrypt the EncryptedColumnEncryptionKey
// Format is
// version + keyPathLength + ciphertextLength + keyPath + ciphervtext + signature
//
// keyPath is present in the encrypted column encryption key for identifying the original source of the asymmetric key pair and
// we will not validate it against the data contained in the CMK metadata (masterKeyPath).
// Validate the version byte
if (encryptedColumnEncryptionKey[0] != _version[0])
{
throw SQL.InvalidAlgorithmVersionInEncryptedCEK(encryptedColumnEncryptionKey[0], _version[0]);
}
// Get key path length
int currentIndex = _version.Length;
UInt16 keyPathLength = BitConverter.ToUInt16(encryptedColumnEncryptionKey, currentIndex);
currentIndex += sizeof(UInt16);
// Get ciphertext length
UInt16 cipherTextLength = BitConverter.ToUInt16(encryptedColumnEncryptionKey, currentIndex);
currentIndex += sizeof(UInt16);
// Skip KeyPath
// KeyPath exists only for troubleshooting purposes and doesnt need validation.
currentIndex += keyPathLength;
// validate the ciphertext length
if (cipherTextLength != keySizeInBytes)
{
throw SQL.InvalidCiphertextLengthInEncryptedCEKCsp(cipherTextLength, keySizeInBytes, masterKeyPath);
}
// Validate the signature length
// Signature length should be same as the key side for RSA PKCSv1.5
int signatureLength = encryptedColumnEncryptionKey.Length - currentIndex - cipherTextLength;
if (signatureLength != keySizeInBytes)
{
throw SQL.InvalidSignatureInEncryptedCEKCsp(signatureLength, keySizeInBytes, masterKeyPath);
}
// Get ciphertext
byte[] cipherText = new byte[cipherTextLength];
Buffer.BlockCopy(encryptedColumnEncryptionKey, currentIndex, cipherText, 0, cipherText.Length);
currentIndex += cipherTextLength;
// Get signature
byte[] signature = new byte[signatureLength];
Buffer.BlockCopy(encryptedColumnEncryptionKey, currentIndex, signature, 0, signature.Length);
// Compute the hash to validate the signature
byte[] hash;
using (SHA256Cng sha256 = new SHA256Cng())
{
sha256.TransformFinalBlock(encryptedColumnEncryptionKey, 0, encryptedColumnEncryptionKey.Length - signature.Length);
hash = sha256.Hash;
}
Debug.Assert(hash != null, @"hash should not be null while decrypting encrypted column encryption key.");
// Validate the signature
if (!RSAVerifySignature(hash, signature, rsaProvider))
{
throw SQL.InvalidSignature(masterKeyPath);
}
// Decrypt the CEK
return RSADecrypt(rsaProvider, cipherText);
}
/// <summary>
/// This function uses the asymmetric key specified by the key path
/// and encrypts CEK with RSA encryption algorithm.
/// </summary>
/// <param name="keyPath">Complete path of an asymmetric key in AKV</param>
/// <param name="encryptionAlgorithm">Asymmetric Key Encryption Algorithm</param>
/// <param name="columnEncryptionKey">Plain text column encryption key</param>
/// <returns>Encrypted column encryption key</returns>
public override byte[] EncryptColumnEncryptionKey(string masterKeyPath, string encryptionAlgorithm, byte[] columnEncryptionKey)
{
// Validate the input parameters
ValidateNonEmptyCSPKeyPath(masterKeyPath, isSystemOp: false);
if (null == columnEncryptionKey)
{
throw SQL.NullColumnEncryptionKey();
}
else if (0 == columnEncryptionKey.Length)
{
throw SQL.EmptyColumnEncryptionKey();
}
// Validate encryptionAlgorithm
ValidateEncryptionAlgorithm(encryptionAlgorithm, isSystemOp: false);
// Create RSA Provider with the given CSP name and key name
RSACryptoServiceProvider rsaProvider = CreateRSACryptoProvider(masterKeyPath, isSystemOp: false);
// Validate whether the key is RSA one or not and then get the key size
int keySizeInBytes = GetKeySize(rsaProvider);
// Construct the encryptedColumnEncryptionKey
// Format is
// version + keyPathLength + ciphertextLength + ciphertext + keyPath + signature
//
// We currently only support one version
byte[] version = new byte[] { _version[0] };
// Get the Unicode encoded bytes of cultureinvariant lower case masterKeyPath
byte[] masterKeyPathBytes = Encoding.Unicode.GetBytes(masterKeyPath.ToLowerInvariant());
byte[] keyPathLength = BitConverter.GetBytes((Int16)masterKeyPathBytes.Length);
// Encrypt the plain text
byte[] cipherText = RSAEncrypt(rsaProvider, columnEncryptionKey);
byte[] cipherTextLength = BitConverter.GetBytes((Int16)cipherText.Length);
Debug.Assert(cipherText.Length == keySizeInBytes, @"cipherText length does not match the RSA key size");
// Compute hash
// SHA-2-256(version + keyPathLength + ciphertextLength + keyPath + ciphertext)
byte[] hash;
using (SHA256Cng sha256 = new SHA256Cng())
{
sha256.TransformBlock(version, 0, version.Length, version, 0);
sha256.TransformBlock(keyPathLength, 0, keyPathLength.Length, keyPathLength, 0);
sha256.TransformBlock(cipherTextLength, 0, cipherTextLength.Length, cipherTextLength, 0);
sha256.TransformBlock(masterKeyPathBytes, 0, masterKeyPathBytes.Length, masterKeyPathBytes, 0);
sha256.TransformFinalBlock(cipherText, 0, cipherText.Length);
hash = sha256.Hash;
}
// Sign the hash
byte[] signedHash = RSASignHashedData(hash, rsaProvider);
Debug.Assert(signedHash.Length == keySizeInBytes, @"signed hash length does not match the RSA key size");
Debug.Assert(RSAVerifySignature(hash, signedHash, rsaProvider), @"Invalid signature of the encrypted column encryption key computed.");
// Construct the encrypted column encryption key
// EncryptedColumnEncryptionKey = version + keyPathLength + ciphertextLength + keyPath + ciphertext + signature
int encryptedColumnEncryptionKeyLength = version.Length + cipherTextLength.Length + keyPathLength.Length + cipherText.Length + masterKeyPathBytes.Length + signedHash.Length;
byte[] encryptedColumnEncryptionKey = new byte[encryptedColumnEncryptionKeyLength];
// Copy version byte
int currentIndex = 0;
Buffer.BlockCopy(version, 0, encryptedColumnEncryptionKey, currentIndex, version.Length);
currentIndex += version.Length;
// Copy key path length
Buffer.BlockCopy(keyPathLength, 0, encryptedColumnEncryptionKey, currentIndex, keyPathLength.Length);
currentIndex += keyPathLength.Length;
// Copy ciphertext length
Buffer.BlockCopy(cipherTextLength, 0, encryptedColumnEncryptionKey, currentIndex, cipherTextLength.Length);
currentIndex += cipherTextLength.Length;
// Copy key path
Buffer.BlockCopy(masterKeyPathBytes, 0, encryptedColumnEncryptionKey, currentIndex, masterKeyPathBytes.Length);
currentIndex += masterKeyPathBytes.Length;
// Copy ciphertext
Buffer.BlockCopy(cipherText, 0, encryptedColumnEncryptionKey, currentIndex, cipherText.Length);
currentIndex += cipherText.Length;
// copy the signature
Buffer.BlockCopy(signedHash, 0, encryptedColumnEncryptionKey, currentIndex, signedHash.Length);
return encryptedColumnEncryptionKey;
}
/// <summary>
/// Throws NotSupportedException. In this version of .NET Framework this provider does not support signing column master key metadata.
/// </summary>
/// <param name="masterKeyPath">Complete path of an asymmetric key. Path format is specific to a key store provider.</param>
/// <param name="allowEnclaveComputations">Boolean indicating whether this key can be sent to trusted enclave</param>
/// <returns>Encrypted column encryption key</returns>
public override byte[] SignColumnMasterKeyMetadata(string masterKeyPath, bool allowEnclaveComputations)
{
throw new NotSupportedException();
}
/// <summary>
/// Throws NotSupportedException. In this version of .NET Framework this provider does not support verifying signatures of column master key metadata.
/// </summary>
/// <param name="masterKeyPath">Complete path of an asymmetric key. Path format is specific to a key store provider.</param>
/// <param name="allowEnclaveComputations">Boolean indicating whether this key can be sent to trusted enclave</param>
/// <param name="signature">Signature for the master key metadata</param>
/// <returns>Boolean indicating whether the master key metadata can be verified based on the provided signature</returns>
public override bool VerifyColumnMasterKeyMetadata(string masterKeyPath, bool allowEnclaveComputations, byte[] signature)
{
throw new NotSupportedException();
}
/// <summary>
/// This function validates that the encryption algorithm is RSA_OAEP and if it is not,
/// then throws an exception
/// </summary>
/// <param name="encryptionAlgorithm">Asymmetric key encryptio algorithm</param>
/// <param name="isSystemOp">Indicates if ADO.NET calls or the customer calls the API</param>
private void ValidateEncryptionAlgorithm(string encryptionAlgorithm, bool isSystemOp)
{
// This validates that the encryption algorithm is RSA_OAEP
if (null == encryptionAlgorithm)
{
throw SQL.NullKeyEncryptionAlgorithm(isSystemOp);
}
if (string.Equals(encryptionAlgorithm, RSAEncryptionAlgorithmWithOAEP, StringComparison.OrdinalIgnoreCase) != true)
{
throw SQL.InvalidKeyEncryptionAlgorithm(encryptionAlgorithm, RSAEncryptionAlgorithmWithOAEP, isSystemOp);
}
}
/// <summary>
/// Checks if the CSP key path is Empty or Null (and raises exception if they are).
/// </summary>
/// <param name="masterKeyPath">CSP key path.</param>
/// <param name="isSystemOp">Indicates if ADO.NET calls or the customer calls the API</param>
private void ValidateNonEmptyCSPKeyPath(string masterKeyPath, bool isSystemOp)
{
if (string.IsNullOrWhiteSpace(masterKeyPath))
{
if (null == masterKeyPath)
{
throw SQL.NullCspKeyPath(isSystemOp);
}
else
{
throw SQL.InvalidCspPath(masterKeyPath, isSystemOp);
}
}
}
/// <summary>
/// Encrypt the text using specified CSP key.
/// </summary>
/// <param name="masterKeyPath">CSP key path.</param>
/// <param name="encryptionAlgorithm">Encryption Algorithm.</param>
/// <param name="columnEncryptionKey">Plain text Column Encryption Key.</param>
/// <returns>Returns an encrypted blob or throws an exception if there are any errors.</returns>
private byte[] RSAEncrypt(RSACryptoServiceProvider rscp, byte[] columnEncryptionKey)
{
Debug.Assert(columnEncryptionKey != null);
Debug.Assert(rscp != null);
return rscp.Encrypt(columnEncryptionKey, fOAEP: true);
}
/// <summary>
/// Decrypt the text using specified CSP key.
/// </summary>
/// <param name="masterKeyPath">CSP key url.</param>
/// <param name="encryptionAlgorithm">Encryption Algorithm.</param>
/// <param name="encryptedColumnEncryptionKey">Encrypted Column Encryption Key.</param>
/// <returns>Returns the decrypted plaintext Column Encryption Key or throws an exception if there are any errors.</returns>
private byte[] RSADecrypt(RSACryptoServiceProvider rscp, byte[] encryptedColumnEncryptionKey)
{
Debug.Assert((encryptedColumnEncryptionKey != null) && (encryptedColumnEncryptionKey.Length != 0));
Debug.Assert(rscp != null);
return rscp.Decrypt(encryptedColumnEncryptionKey, fOAEP: true);
}
/// <summary>
/// Generates signature based on RSA PKCS#v1.5 scheme using a specified CSP Key URL.
/// </summary>
/// <param name="dataToSign">Text to sign.</param>
/// <param name="rscp">RSA Provider with a given key</param>
/// <returns>Signature</returns>
private byte[] RSASignHashedData(byte[] dataToSign, RSACryptoServiceProvider rscp)
{
Debug.Assert((dataToSign != null) && (dataToSign.Length != 0));
Debug.Assert(rscp != null);
return rscp.SignData(dataToSign, HashingAlgorithm);
}
/// <summary>
/// Verifies the given RSA PKCSv1.5 signature.
/// </summary>
/// <param name="dataToVerify"></param>
/// <param name="signature"></param>
/// <param name="rscp">RSA Provider with a given key</param>
/// <returns>true if signature is valid, false if it is not valid</returns>
private bool RSAVerifySignature(byte[] dataToVerify, byte[] signature, RSACryptoServiceProvider rscp)
{
Debug.Assert((dataToVerify != null) && (dataToVerify.Length != 0));
Debug.Assert((signature != null) && (signature.Length != 0));
Debug.Assert(rscp != null);
return rscp.VerifyData(dataToVerify, HashingAlgorithm, signature);
}
/// <summary>
/// Gets the public Key size in bytes
/// </summary>
/// <param name="rscp">RSA Provider with a given key</param>
/// <returns>Key size in bytes</returns>
private int GetKeySize(RSACryptoServiceProvider rscp)
{
Debug.Assert(rscp != null);
return rscp.KeySize / 8;
}
/// <summary>
/// Creates a RSACryptoServiceProvider from the given key path which contains both CSP name and key name
/// </summary>
/// <param name="keyPath">key path in the format of [CAPI provider name]\[key name]</param>
/// <param name="isSystemOp">Indicates if ADO.NET calls or the customer calls the API</param>
/// <returns></returns>
private RSACryptoServiceProvider CreateRSACryptoProvider(string keyPath, bool isSystemOp)
{
// Get CNGProvider and the KeyID
string cspProviderName;
string keyName;
GetCspProviderAndKeyName(keyPath, isSystemOp, out cspProviderName, out keyName);
// Verify the existence of CSP and then get the provider type
int providerType = GetProviderType(cspProviderName, keyPath, isSystemOp);
// Create a new instance of CspParameters for an RSA container.
CspParameters cspParams = new CspParameters(providerType, cspProviderName, keyName);
cspParams.Flags = CspProviderFlags.UseExistingKey;
RSACryptoServiceProvider rscp = null;
try
{
//Create a new instance of RSACryptoServiceProvider
rscp = new RSACryptoServiceProvider(cspParams);
}
catch (CryptographicException e)
{
const int KEYSETDOESNOTEXIST = -2146893802;
if (e.HResult == KEYSETDOESNOTEXIST)
{
// Key does not exist
throw SQL.InvalidCspKeyIdentifier(keyName, keyPath, isSystemOp);
}
else
{
// bubble up the exception
throw;
}
}
return rscp;
}
/// <summary>
/// Extracts the CSP provider name and key name from the given key path
/// </summary>
/// <param name="keyPath">key path in the format of [CSP provider name]\[key name]</param>
/// <param name="isSystemOp">Indicates if ADO.NET calls or the customer calls the API</param>
/// <param name="cspProviderName">output containing the CSP provider name</param>
/// <param name="keyIdentifier">output containing the key name</param>
private void GetCspProviderAndKeyName(string keyPath, bool isSystemOp, out string cspProviderName, out string keyIdentifier)
{
int indexOfSlash = keyPath.IndexOf(@"/");
if (indexOfSlash == -1)
{
throw SQL.InvalidCspPath(keyPath, isSystemOp);
}
cspProviderName = keyPath.Substring(0, indexOfSlash);
keyIdentifier = keyPath.Substring(indexOfSlash + 1, keyPath.Length - (indexOfSlash + 1));
if (cspProviderName.Length == 0)
{
throw SQL.EmptyCspName(keyPath, isSystemOp);
}
if (keyIdentifier.Length == 0)
{
throw SQL.EmptyCspKeyId(keyPath, isSystemOp);
}
}
/// <summary>
/// Gets the provider type from a given CAPI provider name
/// </summary>
/// <param name="providerName">CAPI provider name</param>
/// <param name="keyPath">key path in the format of [CSP provider name]\[key name]</param>
/// <param name="isSystemOp">Indicates if ADO.NET calls or the customer calls the API</param>
/// <returns></returns>
private int GetProviderType(string providerName, string keyPath, bool isSystemOp)
{
string keyName = String.Format(@"SOFTWARE\Microsoft\Cryptography\Defaults\Provider\{0}", providerName);
RegistryKey key = Registry.LocalMachine.OpenSubKey(keyName);
if (key == null)
{
throw SQL.InvalidCspName(providerName, keyPath, isSystemOp);
}
int providerType = (int)key.GetValue(@"Type");
key.Close();
return providerType;
}
}
}
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