RC4 (jl)

using OffsetArrays

mutable struct RC4
    state::OffsetArray{UInt8}
    i::UInt8
    j::UInt8
    RC4()=new(OffsetArray([ UInt8(i) for i in 0:255 ],-1),0,0)
end

function getRC4(k::OffsetArray{UInt8})
    enc=RC4()
    j::UInt8=0
    for i=0:255
        j+=enc.state[i]+k[i%length(k)]
        enc.state[[i,j]]=enc.state[[j,i]]
    end
    enc
end

function getRC4(k::Array)
    getRC4(OffsetArray(k,-1))
end

function getRC4(k::String)
    getRC4(Array{UInt8}(k))
end

function getencryptor(enc::RC4)
    function encode(c::Channel)
        while true
            enc.i+=1
            enc.j+=enc.state[enc.i]
            enc.state[[enc.i,enc.j]]=enc.state[[enc.j,enc.i]]
            k=enc.state[enc.state[enc.i]+enc.state[enc.j]]
            put!(c,k)
        end
    end
end

function encrypt(enc::RC4,text::Array{UInt8})
    stream=Channel(getencryptor(enc))
    String([ c⊻take!(stream) for c in text])
end

function encrypt(enc::RC4,text::String)
    encrypt(enc,Array{UInt8}(text))
end

M="This is a secret message which we want to encode"
cc=getRC4("Secret")
E=encrypt(cc,M)

cc=getRC4("Secret")
D=encrypt(cc,E)