public KeyRing(IHostingEnvironment hostingEnvironment)
{
// Create the keyring directory if one doesn't exist.
var keyRingDirectory = Path.Combine(hostingEnvironment.ContentRootPath, "keyring");
Directory.CreateDirectory(keyRingDirectory);
var directoryInfo = new DirectoryInfo(keyRingDirectory);
if (directoryInfo.GetFiles("*.key").Length == 0)
{
ProtectorAlgorithmHelper.GetAlgorithms(
ProtectorAlgorithmHelper.DefaultAlgorithm,
out SymmetricAlgorithm encryptionAlgorithm,
out KeyedHashAlgorithm signingAlgorithm,
out int derivationCount);
encryptionAlgorithm.GenerateKey();
var keyAsString = Convert.ToBase64String(encryptionAlgorithm.Key);
var keyId = Guid.NewGuid().ToString();
var keyFileName = Path.Combine(keyRingDirectory, keyId + ".key");
using (var file = File.CreateText(keyFileName))
{
file.WriteLine(keyAsString);
}
_keyDictionary.Add(keyId, keyAsString);
CurrentKeyId = keyId;
encryptionAlgorithm.Clear();
encryptionAlgorithm.Dispose();
signingAlgorithm.Dispose();
}
else
{
var filesOrdered = directoryInfo.EnumerateFiles()
.OrderByDescending(d => d.CreationTime)
.Select(d => d.Name)
.ToList();
foreach (var fileName in filesOrdered)
{
var keyFileName = Path.Combine(keyRingDirectory, fileName);
var key = File.ReadAllText(keyFileName);
var keyId = Path.GetFileNameWithoutExtension(fileName);
_keyDictionary.Add(keyId, key);
CurrentKeyId = keyId;
}
}
}
public string Unprotect(string keyId, string data)
{
var masterKey = MasterKey(keyId);
byte[] plainText;
// Take our string and convert it back to bytes.
var payload = Convert.FromBase64String(data);
// Read the saved algorithm details and create instances of those algorithms.
byte[] algorithmIdentifierAsBytes = new byte[4];
Buffer.BlockCopy(payload, 0, algorithmIdentifierAsBytes, 0, 4);
var algorithmIdentifier = (ProtectorAlgorithm)(BitConverter.ToInt32(algorithmIdentifierAsBytes, 0));
ProtectorAlgorithmHelper.GetAlgorithms(
_defaultAlgorithm,
out SymmetricAlgorithm encryptingAlgorithm,
out KeyedHashAlgorithm signingAlgorithm,
out int keyDerivationIterationCount);
// Now extract the signature
byte[] signature = new byte[signingAlgorithm.HashSize / 8];
Buffer.BlockCopy(payload, 4, signature, 0, signingAlgorithm.HashSize / 8);
// And finally grab the rest of the data
var dataLength = payload.Length - 4 - signature.Length;
byte[] cipherTextAndIV = new byte[dataLength];
Buffer.BlockCopy(payload, 4 + signature.Length, cipherTextAndIV, 0, dataLength);
// Check the signature before anything else is done to detect tampering and avoid
// oracles.
byte[] computedSignature = SignData(
cipherTextAndIV,
masterKey,
encryptingAlgorithm,
signingAlgorithm,
keyDerivationIterationCount);
if (!ByteArraysEqual(computedSignature, signature))
{
throw new CryptographicException(@"Invalid Signature.");
}
signingAlgorithm.Clear();
signingAlgorithm.Dispose();
// The signature is valid, so now we can work on decrypting the data.
var ivLength = encryptingAlgorithm.BlockSize / 8;
byte[] initializationVector = new byte[ivLength];
byte[] cipherText = new byte[cipherTextAndIV.Length - ivLength];
// The IV is embedded in the cipher text, so we extract it out.
Buffer.BlockCopy(cipherTextAndIV, 0, initializationVector, 0, ivLength);
// Then we get the encrypted data.
Buffer.BlockCopy(cipherTextAndIV, ivLength, cipherText, 0, cipherTextAndIV.Length - ivLength);
encryptingAlgorithm.Key = DerivedEncryptionKey(
masterKey,
encryptingAlgorithm,
keyDerivationIterationCount);
encryptingAlgorithm.IV = initializationVector;
// Decrypt
using (var ms = new MemoryStream())
using (var cs = new CryptoStream(ms, encryptingAlgorithm.CreateDecryptor(), CryptoStreamMode.Write))
{
cs.Write(cipherText);
cs.FlushFinalBlock();
plainText = ms.ToArray();
}
encryptingAlgorithm.Clear();
encryptingAlgorithm.Dispose();
// And convert from the bytes back to a string.
return(Encoding.UTF8.GetString(plainText));
}
public string Protect(string keyId, string data)
{
// Get the default algorithms.
// We does this so we can embed the algorithm details used in the cipher text so we can
// change algorithms as yet another collision appears in a hashing algorithm.
// See https://media.blackhat.com/bh-us-10/whitepapers/Sullivan/BlackHat-USA-2010-Sullivan-Cryptographic-Agility-wp.pdf
ProtectorAlgorithmHelper.GetAlgorithms(
_defaultAlgorithm,
out SymmetricAlgorithm encryptingAlgorithm,
out KeyedHashAlgorithm signingAlgorithm,
out int keyDerivationIterationCount);
var masterKey = MasterKey(keyId);
// Convert the string to bytes, because encryption works on bytes, not strings.
var plainText = Encoding.UTF8.GetBytes(data);
byte[] cipherTextAndIV;
// Derive a key for encryption from the master key
encryptingAlgorithm.Key = DerivedEncryptionKey(
masterKey,
encryptingAlgorithm,
keyDerivationIterationCount);
// As we need this to be deterministic, we need to force an IV that is derived from the plain text.
encryptingAlgorithm.IV = DerivedInitializationVector(
masterKey,
data,
encryptingAlgorithm,
keyDerivationIterationCount);
// And encrypt
using (var ms = new MemoryStream())
using (var cs = new CryptoStream(
ms,
encryptingAlgorithm.CreateEncryptor(),
CryptoStreamMode.Write))
{
cs.Write(plainText);
cs.FlushFinalBlock();
var encryptedData = ms.ToArray();
cipherTextAndIV = CombineByteArrays(encryptingAlgorithm.IV, encryptedData);
}
// Now get a signature for the data so we can detect tampering in situ.
byte[] signature = SignData(
cipherTextAndIV,
masterKey,
encryptingAlgorithm,
signingAlgorithm,
keyDerivationIterationCount);
// Add the signature to the cipher text.
var signedData = CombineByteArrays(signature, cipherTextAndIV);
// Add our algorithm identifier to the combined signature and cipher text.
var algorithmIdentifier = BitConverter.GetBytes((int)_defaultAlgorithm);
byte[] output = CombineByteArrays(algorithmIdentifier, signedData);
// Clean everything up.
encryptingAlgorithm.Clear();
signingAlgorithm.Clear();
encryptingAlgorithm.Dispose();
signingAlgorithm.Dispose();
Array.Clear(plainText, 0, plainText.Length);
// Return the results as a string.
return(Convert.ToBase64String(output));
}