Yandex wordstat encrypted AJAX decoder for Python and Erlang

decode_wordstat.erl

decode_data(Data, UserAgent, Fuid01) ->
    Key = iolist_to_binary([binary:part(UserAgent, 0, min(25, size(UserAgent))),
                            Fuid01,
                            <<"I keep watch over you ;)">>]),
    decode_chars(Data, Key, 0).

decode_chars(<<>>, _, _) ->
    <<>>;
decode_chars(<<Char:8, Rest/binary>>, Key, Idx) ->
    KeyPos = Idx rem size(Key),
    <<_:KeyPos/binary, KeyChr:8, _/binary>> = Key,
    Decoded = Char bxor KeyChr,
    Next = decode_chars(Rest, Key, Idx + 1),
    <<Decoded:8, Next/binary>>.

decode_wordstat.js

function decode_wordstat(l) {
     var h = navigator['userAgent']['substr'](0, 25) + $['cookie']('fuid01') + 'I keep watch over you ;)';
    var n = '';
    for (var g = 0; g < l['data']['length']; g++) {
        n = n + String['fromCharCode'](l['data']['charCodeAt'](g) ^ h['charCodeAt'](g % h['length']))
    }
    return n
}

decode_wordstat.py

def decode_wordstat(response_data, user_agent, fuid01):
    key = user_agent[:25] + fuid01 + 'I keep watch over you ;)'
    res = ''
    for i, char in enumerate(response_data):
        decoded = chr(ord(char) ^ ord(key[i % len(key)]))
        res += decoded
    return res