Solving each and every TJCTF-2018 challenge

Write-up of all the TJCTF-2018 challenges

I deleted all my repositories on walk-through over CTF challenges and now am blogging them away.

Repository no longer available.

TJCTF 2018

TJCTF is a Capture the Flag (CTF) competition hosted by TJHSST’s Computer Security Club. It is an online, jeopardy-style competition targeted at high schoolers interested in Computer Science and Cybersecurity.

Problem List

  • Blank (5 points)
  • Trippy (5 points)
  • Weird Logo (5 points)
  • Discord! (5 points)
  • Cookie Monster (10 points)
  • Central Savings Account (10 points)
  • Vinegar (15 points)
  • Interference (15 points)
  • Math Whiz (20 points)
  • Nothing but Everything (20 points)
  • Caesar’s Complication (20 points)
  • Huuuuuge (25 points)
  • Learn My Flag (30 points)
  • Request Me (30 points)
  • Validator (30 points)
  • Classic (40 points)
  • Speedy Security (40 points)
  • Python Reversing (40 points)
  • Ess Kyoo Ell (40 points)
  • Tilted Troop (40 points)
  • Lexington State Bank (40 points)
  • RC4 took an L (40 points)
  • Moar Horses (40 points)
  • Grid Parser (45 points)
  • Bad Cipher (50 points)
  • Weird Audio Circuit (50 points)
  • Sarah’s Cryptosystem (60 points)
  • Programmable Hyperlinked Pasta (60 points)
  • Permutations (70 points)
  • Ssleepy (70 points)
  • We Will Rock You (75 points)
  • PIT or Miss (80 points)
  • Bricked Binary (80 points)
  • Future Canary Lab (80 points)
  • Moar Turtles (80 points)
  • Affine (90 points)
  • Online Banking (90 points)
  • Mirror Mirror (100 points)
  • Secure Secrets (110 points)
  • Volatile Virus (130 points)
  • Stupid Blog (130 points)
  • Super Secure Secrets (1(40 points)
  • The Abyss (160 points)

Blank

Web - Unsolved (979 solves)

Challenge Statement

Someone told me there was a flag on this site, so why is it that I can only see blank?

Solution

$ curl -s https://blank.tjctf.org/ | grep 'tjctf'
<!-- flag: tjctf{50urc3_c0d3_n3v3r_l0535} -->

Trippy

Miscellaneous - Unsolved (515 solves)

Challenge Statement

trippy

Solution

$ curl -s https://2018static.tjctf.org/be37fef78cfd6c7deda71154f567e6d0cfefbda1f80698c064bab469d3a54c58_trippy.gif > be37fef78cfd6c7deda71154f567e6d0cfefbda1f80698c064bab469d3a54c58_trippy.gif
$ ./strings be37fef78cfd6c7deda71154f567e6d0cfefbda1f80698c064bab469d3a54c58_trippy.gif | grep 'tjctf'
tjctf{w0w}

Weird Logo

Forensics - Unsolved (606 solves)

Challenge Statement

This company’s logo stands in contrast of those of other leading edge tech companies with its poor design

Source

Solution

  • Opening the Image in StegSolve
  • Moving to Random color map 3

Discord!

Skipping …

Cookie Monster

Web - Unsolved (821 solves)

Challenge Statement

The Cookie Monster is not a fan of horses

Solution

Central Savings Account

Unsolved (612 solves)

Challenge Statement

I seem to have forgotten the password for my savings account. What am I gonna do?

The flag is not in standard flag format.

Solution

$ curl -s https://central_savings_account.tjctf.org/static/main.js
var md5 = function (string) {
function RotateLeft(lValue, iShiftBits) {
return (lValue<<iShiftBits) | (lValue>>>(32-iShiftBits));
}
function AddUnsigned(lX,lY) {
var lX4,lY4,lX8,lY8,lResult;
lX8 = (lX & 0x80000000);
lY8 = (lY & 0x80000000);
lX4 = (lX & 0x40000000);
lY4 = (lY & 0x40000000);
lResult = (lX & 0x3FFFFFFF)+(lY & 0x3FFFFFFF);
if (lX4 & lY4) {
return (lResult ^ 0x80000000 ^ lX8 ^ lY8);
}
if (lX4 | lY4) {
if (lResult & 0x40000000) {
return (lResult ^ 0xC0000000 ^ lX8 ^ lY8);
} else {
return (lResult ^ 0x40000000 ^ lX8 ^ lY8);
}
} else {
return (lResult ^ lX8 ^ lY8);
}
}
function F(x,y,z) { return (x & y) | ((~x) & z); }
function G(x,y,z) { return (x & z) | (y & (~z)); }
function H(x,y,z) { return (x ^ y ^ z); }
function I(x,y,z) { return (y ^ (x | (~z))); }
function FF(a,b,c,d,x,s,ac) {
a = AddUnsigned(a, AddUnsigned(AddUnsigned(F(b, c, d), x), ac));
return AddUnsigned(RotateLeft(a, s), b);
};
function GG(a,b,c,d,x,s,ac) {
a = AddUnsigned(a, AddUnsigned(AddUnsigned(G(b, c, d), x), ac));
return AddUnsigned(RotateLeft(a, s), b);
};
function HH(a,b,c,d,x,s,ac) {
a = AddUnsigned(a, AddUnsigned(AddUnsigned(H(b, c, d), x), ac));
return AddUnsigned(RotateLeft(a, s), b);
};
function II(a,b,c,d,x,s,ac) {
a = AddUnsigned(a, AddUnsigned(AddUnsigned(I(b, c, d), x), ac));
return AddUnsigned(RotateLeft(a, s), b);
};
function ConvertToWordArray(string) {
var lWordCount;
var lMessageLength = string.length;
var lNumberOfWords_temp1=lMessageLength + 8;
var lNumberOfWords_temp2=(lNumberOfWords_temp1-(lNumberOfWords_temp1 % 64))/64;
var lNumberOfWords = (lNumberOfWords_temp2+1)*16;
var lWordArray=Array(lNumberOfWords-1);
var lBytePosition = 0;
var lByteCount = 0;
while ( lByteCount < lMessageLength ) {
lWordCount = (lByteCount-(lByteCount % 4))/4;
lBytePosition = (lByteCount % 4)*8;
lWordArray[lWordCount] = (lWordArray[lWordCount] | (string.charCodeAt(lByteCount)<<lBytePosition));
lByteCount++;
}
lWordCount = (lByteCount-(lByteCount % 4))/4;
lBytePosition = (lByteCount % 4)*8;
lWordArray[lWordCount] = lWordArray[lWordCount] | (0x80<<lBytePosition);
lWordArray[lNumberOfWords-2] = lMessageLength<<3;
lWordArray[lNumberOfWords-1] = lMessageLength>>>29;
return lWordArray;
};
function WordToHex(lValue) {
var WordToHexValue="",WordToHexValue_temp="",lByte,lCount;
for (lCount = 0;lCount<=3;lCount++) {
lByte = (lValue>>>(lCount*8)) & 255;
WordToHexValue_temp = "0" + lByte.toString(16);
WordToHexValue = WordToHexValue + WordToHexValue_temp.substr(WordToHexValue_temp.length-2,2);
}
return WordToHexValue;
};
function Utf8Encode(string) {
string = string.replace(/\r\n/g,"\n");
var utftext = "";
for (var n = 0; n < string.length; n++) { var c = string.charCodeAt(n); if (c < 128) {
utftext += String.fromCharCode(c);
}
else if((c > 127) && (c < 2048)) {
utftext += String.fromCharCode((c >> 6) | 192);
utftext += String.fromCharCode((c & 63) | 128);
}
else {
utftext += String.fromCharCode((c >> 12) | 224);
utftext += String.fromCharCode(((c >> 6) & 63) | 128);
utftext += String.fromCharCode((c & 63) | 128);
}
} return utftext;
};
var x=Array();
var k,AA,BB,CC,DD,a,b,c,d;
var S11=7, S12=12, S13=17, S14=22;
var S21=5, S22=9 , S23=14, S24=20;
var S31=4, S32=11, S33=16, S34=23;
var S41=6, S42=10, S43=15, S44=21;
string = Utf8Encode(string); x = ConvertToWordArray(string); a = 0x67452301; b = 0xEFCDAB89; c = 0x98BADCFE; d = 0x10325476; for (k=0;k<x.length;k+=16) {
AA=a; BB=b; CC=c; DD=d;
a=FF(a,b,c,d,x[k+0], S11,0xD76AA478);
d=FF(d,a,b,c,x[k+1], S12,0xE8C7B756);
c=FF(c,d,a,b,x[k+2], S13,0x242070DB);
b=FF(b,c,d,a,x[k+3], S14,0xC1BDCEEE);
a=FF(a,b,c,d,x[k+4], S11,0xF57C0FAF);
d=FF(d,a,b,c,x[k+5], S12,0x4787C62A);
c=FF(c,d,a,b,x[k+6], S13,0xA8304613);
b=FF(b,c,d,a,x[k+7], S14,0xFD469501);
a=FF(a,b,c,d,x[k+8], S11,0x698098D8);
d=FF(d,a,b,c,x[k+9], S12,0x8B44F7AF);
c=FF(c,d,a,b,x[k+10],S13,0xFFFF5BB1);
b=FF(b,c,d,a,x[k+11],S14,0x895CD7BE);
a=FF(a,b,c,d,x[k+12],S11,0x6B901122);
d=FF(d,a,b,c,x[k+13],S12,0xFD987193);
c=FF(c,d,a,b,x[k+14],S13,0xA679438E);
b=FF(b,c,d,a,x[k+15],S14,0x49B40821);
a=GG(a,b,c,d,x[k+1], S21,0xF61E2562);
d=GG(d,a,b,c,x[k+6], S22,0xC040B340);
c=GG(c,d,a,b,x[k+11],S23,0x265E5A51);
b=GG(b,c,d,a,x[k+0], S24,0xE9B6C7AA);
a=GG(a,b,c,d,x[k+5], S21,0xD62F105D);
d=GG(d,a,b,c,x[k+10],S22,0x2441453);
c=GG(c,d,a,b,x[k+15],S23,0xD8A1E681);
b=GG(b,c,d,a,x[k+4], S24,0xE7D3FBC8);
a=GG(a,b,c,d,x[k+9], S21,0x21E1CDE6);
d=GG(d,a,b,c,x[k+14],S22,0xC33707D6);
c=GG(c,d,a,b,x[k+3], S23,0xF4D50D87);
b=GG(b,c,d,a,x[k+8], S24,0x455A14ED);
a=GG(a,b,c,d,x[k+13],S21,0xA9E3E905);
d=GG(d,a,b,c,x[k+2], S22,0xFCEFA3F8);
c=GG(c,d,a,b,x[k+7], S23,0x676F02D9);
b=GG(b,c,d,a,x[k+12],S24,0x8D2A4C8A);
a=HH(a,b,c,d,x[k+5], S31,0xFFFA3942);
d=HH(d,a,b,c,x[k+8], S32,0x8771F681);
c=HH(c,d,a,b,x[k+11],S33,0x6D9D6122);
b=HH(b,c,d,a,x[k+14],S34,0xFDE5380C);
a=HH(a,b,c,d,x[k+1], S31,0xA4BEEA44);
d=HH(d,a,b,c,x[k+4], S32,0x4BDECFA9);
c=HH(c,d,a,b,x[k+7], S33,0xF6BB4B60);
b=HH(b,c,d,a,x[k+10],S34,0xBEBFBC70);
a=HH(a,b,c,d,x[k+13],S31,0x289B7EC6);
d=HH(d,a,b,c,x[k+0], S32,0xEAA127FA);
c=HH(c,d,a,b,x[k+3], S33,0xD4EF3085);
b=HH(b,c,d,a,x[k+6], S34,0x4881D05);
a=HH(a,b,c,d,x[k+9], S31,0xD9D4D039);
d=HH(d,a,b,c,x[k+12],S32,0xE6DB99E5);
c=HH(c,d,a,b,x[k+15],S33,0x1FA27CF8);
b=HH(b,c,d,a,x[k+2], S34,0xC4AC5665);
a=II(a,b,c,d,x[k+0], S41,0xF4292244);
d=II(d,a,b,c,x[k+7], S42,0x432AFF97);
c=II(c,d,a,b,x[k+14],S43,0xAB9423A7);
b=II(b,c,d,a,x[k+5], S44,0xFC93A039);
a=II(a,b,c,d,x[k+12],S41,0x655B59C3);
d=II(d,a,b,c,x[k+3], S42,0x8F0CCC92);
c=II(c,d,a,b,x[k+10],S43,0xFFEFF47D);
b=II(b,c,d,a,x[k+1], S44,0x85845DD1);
a=II(a,b,c,d,x[k+8], S41,0x6FA87E4F);
d=II(d,a,b,c,x[k+15],S42,0xFE2CE6E0);
c=II(c,d,a,b,x[k+6], S43,0xA3014314);
b=II(b,c,d,a,x[k+13],S44,0x4E0811A1);
a=II(a,b,c,d,x[k+4], S41,0xF7537E82);
d=II(d,a,b,c,x[k+11],S42,0xBD3AF235);
c=II(c,d,a,b,x[k+2], S43,0x2AD7D2BB);
b=II(b,c,d,a,x[k+9], S44,0xEB86D391);
a=AddUnsigned(a,AA);
b=AddUnsigned(b,BB);
c=AddUnsigned(c,CC);
d=AddUnsigned(d,DD);
}
var temp = WordToHex(a)+WordToHex(b)+WordToHex(c)+WordToHex(d); return temp.toLowerCase();
}
$(document).ready(function() {
$("#login-form").submit(function() {
if (md5($("#password").val()).toLowerCase() === "698967f805dea9ea073d188d73ab7390") {
$("html").html("<h1>Login Succeeded!</h1>");
}
else {
$("html").html("<h1>Login Failed!</h1>");
}
})
});

Interesting Snippet

$(document).ready(function() {
$("#login-form").submit(function() {
if (md5($("#password").val()).toLowerCase() === "698967f805dea9ea073d188d73ab7390") {
$("html").html("<h1>Login Succeeded!</h1>");
}
else {
$("html").html("<h1>Login Failed!</h1>");
}
})

Quick check

>>> len("698967f805dea9ea073d188d73ab7390") == 32
True

And then,

Vinegar

Cryptography - Unsolved (428 solves)

Challenge Statement

I just wanted something more than a Caesar salad. Maybe I should order another one? vinegar.txt

Solution

$ curl -s https://2018static.tjctf.org/94d6bb5d5a771ec98d8fd157d4b2f850f594cf15bcd1c9147becc6d3e83bcc79_vinegar.txt | cat
key = Kkkkk kkkkKkkkkkkkkKkkkkkkkkKkk
flag = uucbx{simbjyaqyvzbzfdatshktkbde}
sha256 = 8304c5fa4186bbce7ac030d068fdd485040e65bf824ee70b0bdbac03862bec93

Reference : https://www.dcode.fr/vigenere-cipher

Interference

Miscellaneous - Unsolved (270 solves)

Challenge Statement

I was looking at some images but I couldn’t see them clearly. I think there’s some interference.

Solution

  • Extracting the zip file.
  • Opening the Image named v2.png in StegSolve
  • Moving to Random colour map 3

You get,

  • Saving it using StegSolve as solved.bmp
  • Converting it to PNG and getting the RBG values of the colours.
  • Getting a little Pythonic.
# https://www.ginifab.com/feeds/pms/color_picker_from_image.php for taking RBG valuesfrom PIL import Imageim = Image.open("solved.png")
rgb = im.convert('RGB')
pixels = im.load()
width = im.size[0]
height = im.size[1]
for x in range(0, width):
for y in range(0, height):
color = rgb.getpixel((x, y))
if color== (139,235,135) or color == (228, 224, 139):
pixels[x, y] = (255,255,255)
else:
pixels[x, y] = (0, 0, 0)
im.save("qrcode.png")

Running this script where solved.png is located, you get another image, named, qrcode.png

Looks neat, right?

  • Getting a little bit Pythonic again to decode this via pyzbar

Note : For Linux Users, use zbarimg.Note 2 : For avoiding any frustration : py -m pip install — user pyzbar

>>> from pyzbar.pyzbar import decode
>>> from PIL import Image
>>> decode(Image.open('qrcode.png'))
[Decoded(data=b'tjctf{m1x1ing_and_m4tchIng_1m4g3s_15_fun}', type='QRCODE', rect=Rect(left=33, top=33, width=234, height=234), polygon=[Point(x=33, y=33), Point(x=33, y=266), Point(x=267, y=267), Point(x=266, y=33)])]
>>>

Game over.

tjctf{m1x1ing_and_m4tchIng_1m4g3s_15_fun}

Find TJCTF-2018-master.zip in downloads for scripts and solutions.

Google Code-In C. Winner. GsOCer ‘19. Independent Security Researcher. Have hacked Medium, Mozilla, Opera & many more. Personal Website: https://0x48piraj.com

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