[Lua] CryptoPals Cipher Challenge 1-2

Set1-2.lua

local index_table = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'


function to_binary(integer)
    local remaining = tonumber(integer)
    local bin_bits = ''

    for i = 7, 0, -1 do
        local current_power = math.pow(2, i)

        if remaining >= current_power then
            bin_bits = bin_bits .. '1'
            remaining = remaining - current_power
        else
            bin_bits = bin_bits .. '0'
        end
    end

    return bin_bits
end

function from_binary(bin_bits)
    return tonumber(bin_bits, 2)
end


function string.to_base64(to_encode)
    local bit_pattern = ''
    local encoded = ''
    local trailing = ''

    for i = 1, string.len(to_encode) do
        bit_pattern = bit_pattern .. to_binary(string.byte(string.sub(to_encode, i, i)))
    end

    -- Check the number of bytes. If it's not evenly divisible by three,
    -- zero-pad the ending & append on the correct number of ``=``s.
    if math.mod(string.len(bit_pattern), 3) == 2 then
        trailing = '=='
        bit_pattern = bit_pattern .. '0000000000000000'
    elseif math.mod(string.len(bit_pattern), 3) == 1 then
        trailing = '='
        bit_pattern = bit_pattern .. '00000000'
    end

    for i = 1, string.len(bit_pattern), 6 do
        local byte = string.sub(bit_pattern, i, i+5)
        local offset = tonumber(from_binary(byte))
        encoded = encoded .. string.sub(index_table, offset+1, offset+1)
    end

    return string.sub(encoded, 1, -1 - string.len(trailing)) .. trailing
end


function string.from_base64(to_decode)
    local padded = to_decode:gsub("%s", "")
    local unpadded = padded:gsub("=", "")
    local bit_pattern = ''
    local decoded = ''

    for i = 1, string.len(unpadded) do
        local char = string.sub(to_decode, i, i)
        local offset, _ = string.find(index_table, char)
        if offset == nil then
             error("Invalid character '" .. char .. "' found.")
        end

        bit_pattern = bit_pattern .. string.sub(to_binary(offset-1), 3)
    end

    for i = 1, string.len(bit_pattern), 8 do
        local byte = string.sub(bit_pattern, i, i+7)
        decoded = decoded .. string.char(from_binary(byte))
    end

    local padding_length = padded:len()-unpadded:len()

    if (padding_length == 1 or padding_length == 2) then
        decoded = decoded:sub(1,-2)
    end
    return decoded
end

function string.from_hex(str)
    return (str:gsub('..', function (cc)
        return string.char(tonumber(cc, 16))
    end))
end

function string.to_hex(str)
    return (str:gsub('.', function (c)
        return string.format('%02x', string.byte(c))
    end))
end

function fixedXOR(a,b)
	local out = ""
	for i = 1, #a-1,2 do
		a1 = string.sub(a,i,i+1)
		b1 = string.sub(b,i,i+1)
		a2 = string.byte(a1:from_hex())
		b2 = string.byte(b1:from_hex())
		out = out .. string.char(bit.bxor(a2,b2))
	end
	return (out:to_hex())
end

ciphertext = '1c0111001f010100061a024b53535009181c'
key = '686974207468652062756c6c277320657965'
plaintext = fixedXOR(ciphertext,key)
expected = '746865206b696420646f6e277420706c6179'

io.write('\27[1mCryptoPals Cipher Challenge: Set 1-2\27[m\n\n')
io.write('\27[32mCiphertext: \27[m\t',ciphertext,'\n')
io.write('\27[32mKey: \27[m\t\t',key,'\n')
io.write('\27[32mPlaintext: \27[m\t',plaintext,'\n')
io.write('\27[32mExpected:\27[m\t',expected,'\n')
io.write('\27[32mDecoded:\27[m\t',plaintext:from_hex(),'\n')