Base Sixty Four

wiki

Base64 is also implemented in the b64/unb64 methods in LuaSocket? ([1]), but you may still want to use this snippet for its few requirements -- and it is a nice example with educational value for how to perform logical operations without actual bit-shift or OR operators.

I want to apologize if somebody encountered a serious error with the former version of base64 - Not all logical functions can be easily replaced with mathematical ones, so I had to find a way around. The following code is not as fast as the mime C-Module - yet on smaller values the loading time can make a program slower, too. Find the newest (and corrected) version here:

#!/usr/bin/env lua
-- working lua base64 codec (c) 2006-2008 by Alex Kloss
-- compatible with lua 5.1
-- http://www.it-rfc.de
-- licensed under the terms of the LGPL2

-- bitshift functions (<<, >> equivalent)
-- shift left
function lsh(value,shift)
	return (value*(2^shift)) % 256
end

-- shift right
function rsh(value,shift)
	return math.floor(value/2^shift) % 256
end

-- return single bit (for OR)
function bit(x,b)
	return (x % 2^b - x % 2^(b-1) > 0)
end

-- logic OR for number values
function lor(x,y)
	result = 0
	for p=1,8 do result = result + (((bit(x,p) or bit(y,p)) == true) and 2^(p-1) or 0) end
	return result
end

-- encryption table
local base64chars = {[0]='A',[1]='B',[2]='C',[3]='D',[4]='E',[5]='F',[6]='G',[7]='H',[8]='I',[9]='J',[10]='K',[11]='L',[12]='M',[13]='N',[14]='O',[15]='P',[16]='Q',[17]='R',[18]='S',[19]='T',[20]='U',[21]='V',[22]='W',[23]='X',[24]='Y',[25]='Z',[26]='a',[27]='b',[28]='c',[29]='d',[30]='e',[31]='f',[32]='g',[33]='h',[34]='i',[35]='j',[36]='k',[37]='l',[38]='m',[39]='n',[40]='o',[41]='p',[42]='q',[43]='r',[44]='s',[45]='t',[46]='u',[47]='v',[48]='w',[49]='x',[50]='y',[51]='z',[52]='0',[53]='1',[54]='2',[55]='3',[56]='4',[57]='5',[58]='6',[59]='7',[60]='8',[61]='9',[62]='-',[63]='_'}

-- function encode
-- encodes input string to base64.
function enc(data)
	local bytes = {}
	local result = ""
	for spos=0,string.len(data)-1,3 do
		for byte=1,3 do bytes[byte] = string.byte(string.sub(data,(spos+byte))) or 0 end
		result = string.format('%s%s%s%s%s',result,base64chars[rsh(bytes[1],2)],base64chars[lor(lsh((bytes[1] % 4),4), rsh(bytes[2],4))] or "=",((#data-spos) > 1) and base64chars[lor(lsh(bytes[2] % 16,2), rsh(bytes[3],6))] or "=",((#data-spos) > 2) and base64chars[(bytes[3] % 64)] or "=")
	end
	return result
end

-- decryption table
local base64bytes = {['A']=0,['B']=1,['C']=2,['D']=3,['E']=4,['F']=5,['G']=6,['H']=7,['I']=8,['J']=9,['K']=10,['L']=11,['M']=12,['N']=13,['O']=14,['P']=15,['Q']=16,['R']=17,['S']=18,['T']=19,['U']=20,['V']=21,['W']=22,['X']=23,['Y']=24,['Z']=25,['a']=26,['b']=27,['c']=28,['d']=29,['e']=30,['f']=31,['g']=32,['h']=33,['i']=34,['j']=35,['k']=36,['l']=37,['m']=38,['n']=39,['o']=40,['p']=41,['q']=42,['r']=43,['s']=44,['t']=45,['u']=46,['v']=47,['w']=48,['x']=49,['y']=50,['z']=51,['0']=52,['1']=53,['2']=54,['3']=55,['4']=56,['5']=57,['6']=58,['7']=59,['8']=60,['9']=61,['-']=62,['_']=63,['=']=nil}

-- function decode
-- decode base64 input to string
function dec(data)
	local chars = {}
	local result=""
	for dpos=0,string.len(data)-1,4 do
		for char=1,4 do chars[char] = base64bytes[(string.sub(data,(dpos+char),(dpos+char)) or "=")] end
		result = string.format('%s%s%s%s',result,string.char(lor(lsh(chars[1],2), rsh(chars[2],4))),(chars[3] ~= nil) and string.char(lor(lsh(chars[2],4), rsh(chars[3],2))) or "",(chars[4] ~= nil) and string.char(lor(lsh(chars[3],6) % 192, (chars[4]))) or "")
	end
	return result
end

-- command line if not called as library
if (arg ~= nil) then
	local func = 'enc'
	for n,v in ipairs(arg) do
		if (n > 0) then
			if (v == "-h") then print "base64.lua [-e] [-d] text/data" break
			elseif (v == "-e") then func = 'enc'
			elseif (v == "-d") then func = 'dec'
			else print(_G[func](v)) end
		end
	end
else
	module('base64',package.seeall)
end

On a further notice, I received a mail from someone using my code without acknoledgement of my copyright and license. If you need another license as explicitely stated in the code, feel free to contact me on my email address.