(function () {
    var C = typeof window === 'undefined' ? require('./Crypto').Crypto : window.Crypto;

    // Shortcuts
    var util = C.util;
    var charenc = C.charenc;
    var UTF8 = charenc.UTF8;
    var Binary = charenc.Binary;
    C.PBKDF2 = function (password, salt, keylen, options) {
        // Convert to byte arrays
        if (password.constructor == String) {
            password = UTF8.stringToBytes(password);
        }
        if (salt.constructor == String) {
            salt = UTF8.stringToBytes(salt);
        }
        /* else, assume byte arrays already */

        // Defaults
        var hasher = (options && options.hasher) || C.SHA1;
        var iterations = (options && options.iterations) || 1; // Pseudo-random function
        function PRF(password, salt) {
            return C.HMAC(hasher, salt, password, {
                asBytes: true
            });
        }

        // Generate key
        var derivedKeyBytes = [];
        var blockindex = 1;
        while (derivedKeyBytes.length < keylen) {
            var block = PRF(password, salt.concat(util.wordsToBytes([blockindex])));
            for (var u = block, i = 1; i < iterations; i++) {
                u = PRF(password, u);
                for (var j = 0; j < block.length; j++) {
                    block[j] ^= u[j];
                }
            }
            derivedKeyBytes = derivedKeyBytes.concat(block);
            blockindex++;
        }

        // Truncate excess bytes
        derivedKeyBytes.length = keylen;
        return options && options.asBytes ? derivedKeyBytes : options && options.asString ? Binary.bytesToString(derivedKeyBytes) : util.bytesToHex(derivedKeyBytes);
    };
})();