CTF js-magic

The file received contains javascript obfuscated code.

I first ran it in the obfuscated state: I made a simple html page and put it as a script for that page.

It returned an array which looked like the flag

I then checked what the obfuscated code actually does.

I used this website: https://lelinhtinh.github.io/de4js/ to deobfuscate it.

The important part from the deobfuscated code:

function reverse_string(param) {
    var _15 = param.split('');
    var _16 = _15.reverse();
    var _13 = _16.join('');
    return _13
}

function chunkString(_17, _18) {
    return _17.match(new RegExp('.{1,' + _18 + '}', 'g'))
}

function enc1(param) {
    // adds 0x14 to each character
    nchunk = [];
    for (var i = 0x0; i < param.length; i++) {
        nchunk.push(String.fromCharCode(param[i].charCodeAt() + 0x14))
    }
    return nchunk.join('')
}


function enc2(_9) {
    // substracts 0x14 from each character
    nchunk = [];
    for (var _5 = 0x0; _5 < _9.length; _5++) {
        nchunk.push(String.fromCharCode(_9[_5].charCodeAt() - 0x14))
    }
    return nchunk.join('')
}

function enc3(_19) {
    // reverses the string
    nchunk = reverse_string(_19);
    return nchunk
}

function encode(flag) {
    // alternates between the encryption functions until it fully encrypts the flag
    functs = [enc1, enc2, enc3];
    for (var i = 0x0; i < flag.length; i++) {
        flag[i] = functs[i % 3](flag[i])
        console.log(functs[i % 3](flag[i]))
    }
    return flag
}

The functions I wrote to decrypt the flag:

var flag=
[
  "mk{",
  "\u001bS=",
  "3b0",
  "\\\\",
  "\n\u0011\u0010",
  "fc1",
  "Y\\",
  "\u00119>",
  "bf4",
  "`a",
  "\u0011\u000e>",
  "b92",
  "\\Z_",
  "9=\f",
  "1e4",
  "^\\a",
  ":\u0011\u000b",
  "4ca",
  "\\a]",
  "\u0011\u0011\t",
  "b78",
  "]Z",
  "\u0010\r\r",
  "}"
]

function dec1(param) {
    nchunk = [];
    for (var i = 0x0; i < param.length; i++) {
        nchunk.push(String.fromCharCode(param[i].charCodeAt() - 0x14))
    }
    return nchunk.join('')
}


function dec2(_9) {
    nchunk = [];
    for (var _5 = 0x0; _5 < _9.length; _5++) {
        nchunk.push(String.fromCharCode(_9[_5].charCodeAt() + 0x14))
    }
    return nchunk.join('')
}

function dec3(_19) {
    nchunk = reverse_string(_19);
    return nchunk
}

function decode(flag) {
    functs = [dec1, dec2, dec3];
    for (var i = 0x0; i < flag.length; i++) {
        flag[i] = functs[i % 3](flag[i])
        console.log(functs[i % 3](flag[i]))
    }
}

The output: