/// <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
ValidateNonEmptyKeyPath(masterKeyPath, isSystemOp: false);
if (null == columnEncryptionKey)
{
throw SQL.NullColumnEncryptionKey();
}
else if (0 == columnEncryptionKey.Length)
{
throw SQL.EmptyColumnEncryptionKey();
}
// Validate encryptionAlgorithm
ValidateEncryptionAlgorithm(encryptionAlgorithm, isSystemOp: false);
// CreateCNGProviderWithKey
RSACng rsaCngProvider = CreateRSACngProvider(masterKeyPath, isSystemOp: false);
// Validate whether the key is RSA one or not and then get the key size
int keySizeInBytes = GetKeySize(rsaCngProvider);
// 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(rsaCngProvider, 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, rsaCngProvider);
Debug.Assert(signedHash.Length == keySizeInBytes, @"signed hash length does not match the RSA key size");
Debug.Assert(RSAVerifySignature(hash, signedHash, rsaCngProvider), @"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;
}
