public static bool AuthenticateFile(string filePath, byte[] macKey, out byte[] storedHash)
{
try
{
bool tampered = true;
storedHash = ReadStoredHash(filePath);
if (storedHash != null)
{
byte[] computedHash = new byte[Constants.HashLength];
using (var fileStream = new FileStream(filePath, FileMode.Open, FileAccess.ReadWrite, FileShare.Read, Constants.FileBufferSize, FileOptions.SequentialScan))
{
// Remove the stored MAC from the file before computing the MAC
fileStream.SetLength(fileStream.Length - computedHash.Length);
MemoryEncryption.DecryptByteArray(ref macKey);
computedHash = HashingAlgorithms.Blake2(fileStream, macKey);
MemoryEncryption.EncryptByteArray(ref macKey);
}
// Invert result
tampered = !Sodium.Utilities.Compare(storedHash, computedHash);
if (tampered == true)
{
// Restore the stored MAC
AppendHash(filePath, storedHash);
}
}
return(tampered);
}
catch (Exception ex) when(ExceptionFilters.FileAccessExceptions(ex))
{
Logging.LogException(ex.ToString(), Logging.Severity.High);
DisplayMessage.Error(filePath, ex.GetType().Name, "Unable to authenticate the file.");
storedHash = null;
return(true);
}
}
private static byte[] GetKeyfileBytes(byte[] passwordBytes, string keyfilePath)
{
if (!string.IsNullOrEmpty(keyfilePath))
{
byte[] keyfileBytes = Keyfiles.ReadKeyfile(keyfilePath);
if (keyfileBytes != null)
{
MemoryEncryption.DecryptByteArray(ref passwordBytes);
// Combine password and keyfile bytes
passwordBytes = HashingAlgorithms.Blake2(passwordBytes, keyfileBytes);
MemoryEncryption.EncryptByteArray(ref passwordBytes);
Utilities.ZeroArray(keyfileBytes);
}
}
return(passwordBytes);
}
public static (byte[] encryptionKey, byte[] macKey) DeriveKeys(byte[] passwordBytes, byte[] salt, int iterations, int memorySize)
{
var argon2id = PasswordHash.ArgonAlgorithm.Argon_2ID13;
MemoryEncryption.DecryptByteArray(ref passwordBytes);
// Derive a 96 byte key
byte[] derivedKey = PasswordHash.ArgonHashBinary(passwordBytes, salt, iterations, memorySize, Constants.Argon2KeySize, argon2id);
// 256-bit encryption key
byte[] encryptionKey = new byte[Constants.EncryptionKeySize];
Array.Copy(derivedKey, encryptionKey, encryptionKey.Length);
// 512-bit MAC key
byte[] macKey = new byte[Constants.MACKeySize];
Array.Copy(derivedKey, encryptionKey.Length, macKey, 0, macKey.Length);
Utilities.ZeroArray(derivedKey);
MemoryEncryption.EncryptByteArray(ref passwordBytes);
MemoryEncryption.EncryptByteArray(ref encryptionKey);
MemoryEncryption.EncryptByteArray(ref macKey);
return(encryptionKey, macKey);
}
private static byte[] ComputeFileHash(string encryptedFilePath, byte[] macKey)
{
try
{
byte[] computedHash = new byte[Constants.HashLength];
using (var fileStream = new FileStream(encryptedFilePath, FileMode.Open, FileAccess.Read, FileShare.Read, Constants.FileBufferSize, FileOptions.SequentialScan))
{
MemoryEncryption.DecryptByteArray(ref macKey);
computedHash = HashingAlgorithms.Blake2(fileStream, macKey);
MemoryEncryption.EncryptByteArray(ref macKey);
}
return(computedHash);
}
catch (Exception ex) when(ExceptionFilters.FileAccessExceptions(ex))
{
Logging.LogException(ex.ToString(), Logging.Severity.High);
DisplayMessage.Error(encryptedFilePath, ex.GetType().Name, "Unable to compute MAC.");
return(null);
}
}
private static byte[] HashPasswordBytes(byte[] passwordBytes)
{
passwordBytes = HashingAlgorithms.Blake2(passwordBytes);
MemoryEncryption.EncryptByteArray(ref passwordBytes);
return(passwordBytes);
}