This is a small post about implementing a basic RSA encrypter to encrypt sections in an exe. We can use this to exchange exes with people. We will encrypt the section using the public key and the user has to use his private key to decrypt the exe. This can be applied in evading anti-viruses too.

I will use multiplication instead of an exponent. Since it would be easy to implement in few lines in assembly. However, this will allow breaking the private key easily hence the complete scheme is broken.

$latex Enc = (m*e) \text{ mod } N&bg=FFFFFF&s=1$

$latex Dec = (c*d) \text{ mod } N&bg=FFFFFF&s=1$

The correctness of this scheme depends on the fact that

$latex Dec(Enc(m)) = (m*e*d) \text{ mod } N = m \text{ mod } N&bg=FFFFFF&s=1$