-- RC4

-- http://en.wikipedia.org/wiki/RC4

function KSA(key)

    local key_len = string.len(key)

    local S = {}

    local key_byte = {}

    for i = ,  do

        S[i] = i

    end

    for i = , key_len do

        key_byte[i-] = string.byte(key, i, i)

    end

    local j =

    for i = ,  do

        j = (j + S[i] + key_byte[i % key_len]) %

        S[i], S[j] = S[j], S[i]

    end

    return S

end

function PRGA(S, text_len)

    local i =

    local j =

    local K = {}

    for n = , text_len do

        i = (i + ) %

        j = (j + S[i]) % 

        S[i], S[j] = S[j], S[i]

        K[n] = S[(S[i] + S[j]) % ]

    end

    return K

end

function RC4(key, text)

    local text_len = string.len(text)

    local S = KSA(key)

    local K = PRGA(S, text_len)

    return output(K, text)

end

function output(S, text)

    local len = string.len(text)

    local c = nil

    local res = {}

    for i = , len do

        c = string.byte(text, i, i)

        res[i] = string.char(bxor(S[i], c))

    end

    return table.concat(res)

end

-------------------------------

-------------bit wise-----------

-------------------------------

local bit_op = {}

function bit_op.cond_and(r_a, r_b)

    return (r_a + r_b == ) and  or

end

function bit_op.cond_xor(r_a, r_b)

    return (r_a + r_b == ) and  or

end

function bit_op.cond_or(r_a, r_b)

    return (r_a + r_b > ) and  or

end

function bit_op.base(op_cond, a, b)

    -- bit operation

    if a < b then

        a, b = b, a

    end

    local res =

    local shift =

    while a ~=  do

        r_a = a %

        r_b = b % 

        res = shift * bit_op[op_cond](r_a, r_b) + res

        shift = shift * 

        a = math.modf(a / )

        b = math.modf(b / )

    end

    return res

end

function bxor(a, b)

    return bit_op.base('cond_xor', a, b)

end

function band(a, b)

    return bit_op.base('cond_and', a, b)

end

function bor(a, b)

    return bit_op.base('cond_or', a, b)

end

--key = "Key"

--text = "Plaintext"

--K = RC4(key, text)

--print (K)

--text = RC4(key, K)

--print (text)

--

--key = "Wiki"

--text = "pedia"

--K = RC4(key, text)

--print (K)

--

--key = "Secret"

--text = "Attack at dawn"

--K = RC4(key, text)

--print (K)