RSA_encrypt_decrypt.jl

# Julia-ohjelma RSA_encrypt_decrypt.jl
# originmsg UTF-8 merkistön mukaista tekstiä
# tekstin pituus < julkisen avaimen pituus (77 merkkiä)
# teksti dekoodataan byte-muotoon jotta kelpaa powermod-funtioon
# esimerkissä julkinen avain d on 256-bittinen eli 77 numeroinen
# Juhani Kaukoranta 4.9.2019

function rsaencrypt(originmsg, n, e)
    bytes = parse(BigInt, "0x" * bytes2hex(collect(UInt8, originmsg)))
    return powermod(bytes, e, n)
end

function rsadecrypt(cryptomsg, n, d)
    decoded = powermod(cryptomsg, d, n)
    return join(Char.(hex2bytes(string(decoded,base=16))))
end

originmsg = "Hiphei - hörhöt!"
n = big(98192617636653636141238012338108484137954487342964318282087546585872528680299)
e = 65537
d = big(33574153109097960014509849390092679748726042392305041135147739978253446722693)

cryptomsg = rsaencrypt(originmsg, n, e)
plaintext = rsadecrypt(cryptomsg, n, d)

println("originmsg = ",originmsg)
println("cryptomsg = ",cryptomsg)
println("plaintext = ",plaintext)