private AffineKey CalculateEncryptKey(Signature signature, int encryptedSignatureByte1, int encryptedSignatureByte2)
{
int deltaSignatureBytes = -signature.DeltaBytes; // Yes, I want minus delta.
int deltaEncryptedSygnatureBytes = encryptedSignatureByte1 - encryptedSignatureByte2; // Yes, I want minus delta.
int keyA = Ring.Modulo(deltaEncryptedSygnatureBytes * Ring.Inverse(deltaSignatureBytes, Ring.N), Ring.N);
int keyB = Ring.Modulo(encryptedSignatureByte1 - keyA * signature.Byte1, Ring.N);
AffineKey encryptKey = new AffineKey(keyA, keyB);
return(encryptKey);
}
private AffineKey GetEncryptKey(FileStream inputFileStream, string originalExtension)
{
Signature fileSignature = signatures[originalExtension];
inputFileStream.Position += 1 + originalExtension.Length; // Jump over encrypted extension, where first character means extension length.
long positionBehindEncryptedExtension = inputFileStream.Position;
inputFileStream.Position += fileSignature.Byte1Position;
int encryptedSignatureByte1 = inputFileStream.ReadByte();
inputFileStream.Position = positionBehindEncryptedExtension + fileSignature.Byte2Position;
int encyptedSignatureByte2 = inputFileStream.ReadByte();
inputFileStream.Position = positionBehindEncryptedExtension;
AffineKey encryptKey = CalculateEncryptKey(fileSignature, encryptedSignatureByte1, encyptedSignatureByte2);
return(encryptKey);
}
public async Task DecryptFileAsync(string inputFilePath, string outputFilePath, CancellationToken cancellationToken)
{
AffineKey encryptKey = TryGetEncryptKeyByOutputFilePathWithExtension(inputFilePath, outputFilePath);
await affineCipher.DecryptFileAsync(inputFilePath, outputFilePath, encryptKey, cancellationToken);
}
public void DecryptFile(string inputFilePath, string outputFilePath) // outputFilePath - with CORRECT extension
{
AffineKey encryptKey = TryGetEncryptKeyByOutputFilePathWithExtension(inputFilePath, outputFilePath);
affineCipher.DecryptFile(inputFilePath, outputFilePath, encryptKey);
}