ByteArrayをRC4暗号化する

CriptRC4.as

package {
    import flash.utils.ByteArray;

    public final class CriptRC4 {
        private var        keyCodes    :Vector.
                                        = new Vector.(0, false);
        private const    KEYLENGTH    :uint = 255;

        public function CriptRC4(key:String) {
            keyCodes = new Vector.(KEYLENGTH +1, true);
            const bufCodes:Vector. = new Vector.(KEYLENGTH +1, true);

            const length:uint = key.length;
            var i:uint;
            for (i = 0; i <= KEYLENGTH; ++i) {
                bufCodes[i] = uint(key.charCodeAt(i % length));
                keyCodes[i] = i;
            }
            var j:uint;
            for (j = i = 0; i <= KEYLENGTH; ++i) {
                j = (j + keyCodes[i] + bufCodes[i]) & KEYLENGTH;

                keyCodes[i] ^= keyCodes[j];
                keyCodes[j] ^= keyCodes[i];
                keyCodes[i] ^= keyCodes[j];
            }
        }

        public function cript(data:ByteArray, len:uint=0):ByteArray {
            data.position = 0;
            const length:uint = data.length;
            if ((len == 0) || (len > length)) len = length;

            const buf:Vector. = keyCodes.concat();
            const baRet:ByteArray = new ByteArray();
        //    baRet.position = 0;

            var i:uint;
            var j:uint;
            var k:uint;
            for (i = j = k = 0; k                i = (i + 1) & KEYLENGTH;
                j = (j + buf[i]) & KEYLENGTH;

                buf[i] ^= buf[j];
                buf[j] ^= buf[i];
                buf[i] ^= buf[j];

                const t:uint = (buf[i] + buf[j]) & KEYLENGTH;
                baRet.writeByte(data.readByte() ^ buf[t]);
            }

            if (len < length) baRet.writeBytes(data, data.position);

            return baRet;
        }
    }
}