rc4加密解密

function rc4(data, key) {

    var seq = Array(256);

    var das = Array(data.length);

    for (var i = 0; i < 256; i++) {

        seq[i] = i;

        var j = (j + seq[i] + key.charCodeAt(i % key.length)) % 256;

        var temp = seq[i];

        seq[i] = seq[j];

        seq[j] = temp

    }

    for (var i = 0; i < data.length; i++) {

        das[i] = data.charCodeAt(i)

    }

    for (var x = 0; x < das.length; x++) {

        var i = (i + 1) % 256;

        var j = (j + seq[i]) % 256;

        var temp = seq[i];

        seq[i] = seq[j];

        seq[j] = temp;

        var k = (seq[i] + (seq[j] % 256)) % 256;

        das[x] = String.fromCharCode(das[x] ^ seq[k])

    }

    return das.join('')

}