local b='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'

-- encoding
function b64_enc(data)
     data = string.reverse(data);
     return string.reverse((data:gsub('.', function(x)  
         local r,b='',x:byte()
         for i=8,1,-1 do r=r..(b%2^i-b%2^(i-1)>0 and '1' or '0') end
         return r;
     end)..'0000'):gsub('%d%d%d?%d?%d?%d?', function(x)
         if (#x < 6) then return '' end
         local c=0
         for i=1,6 do c=c+(x:sub(i,i)=='1' and 2^(6-i) or 0) end
         return b:sub(c+1,c+1)
     end)..({ '', '==', '=' })[#data%3+1])
end