A toy RSA implementation written in Haskell as my semestral project for a non-procedural programming course.

cabal install --lib random
make all

# Generate a key:
./toyrsa --gen <keyfile>
# Creates <keyfile> and <keyfile>.pub

# Encrypt something:
./toyrsa --enc <keyfile>

# Decrypt something:
./toyrsa --dec <keyfile>

The program is split into 4 files.

• Main.hs contains the command line interface and padding scheme (which is insecure).
• Lib/Utils.hs contains basic utilities for dealing with large numbers and modular arithmetic. Exponentiation modulo n (only for nonnegative exponents, using exponentiation by squaring) and multiplicative inverse (using a modified Extended Euclidean algorithm).
• Lib/Primes.hs contains the algorithm which generates random primes (by generating random numbers and testing them with the Miller-Rabin primality test)
• Lib/RSA.hs contains the RSA cryptosystem implementation (the most complicated part is the key generation, encryption and decryption is simple modular exponentiation)

The key format is simply a derived Show dump of the PublicKey/PrivateKey types from Lib/RSA.hs.