chrisrzhou/ctf
/picoctf-2019

picoCTF 2019

#unsolved (15)#200pt (14)#general (14)#web (14)#100pt (12)#forensics (11)#50pt (10)#cryptography (10)#grep (10)#400pt (6)#150pt (4)#250pt (4)#ascii (4)#binary (4)#curl (4)#bases (3)#postman (3)#reverse (3)#strings (3)#300pt (2)#awk (2)#bc (2)#nc (2)#sed (2)#sql (2)#vigenere (2)#1pt (1)#350pt (1)#500pt (1)#a1z26 (1)#base64 (1)#brute (1)#caesar (1)#cmp (1)#file (1)#frequency (1)#irish (1)#morsecode (1)#obfuscation (1)#robots (1)#rot13 (1)#tar (1)#tr (1)#unzip (1)#xxd (1)

Overview

https://2019game.picoctf.com/problems solved in bash and js.

The Factory's Secret

#general#unsolved#1pt

There appear to be some mysterious glyphs hidden inside this abandoned factory... I wonder what would happen if you collected them all?

2Warm

#general#50pt#bases#bc

Can you convert the number 42 (base 10) to binary (base 2)?

picoCTF{101010}

echo "obase=2; ibase=10; 42" | bc

Glory of the Garden

#forensics#50pt#strings#grep

This garden contains more than it seems. You can also find the file in /problems/glory-of-the-garden_4_cf9f4aaf458caf5268f8cf0a6465eb98 on the shell server.

picoCTF{more_than_m33ts_the_3y36BCA684D}

No information in the image. Check the string contents.

strings garden.jpg | grep picoCTF{

Insp3ct0r

#web#50pt#curl#grep

Kishor Balan tipped us off that the following code may need inspection: https://2019shell1.picoctf.com/problem/61676/ (link) or http://2019shell1.picoctf.com:61676

picoCTF{tru3_d3t3ct1ve_0r_ju5t_lucky?1638dbe7}

Study the web response using curl and note the clues and related CSS/JS file. curl and grep for relevant terms:

curl https://2019shell1.picoctf.com/problem/61676/
curl https://2019shell1.picoctf.com/problem/61676/ | grep picoCTF{
curl https://2019shell1.picoctf.com/problem/61676/mycss.css | grep flag
curl https://2019shell1.picoctf.com/problem/61676/myjs.js | grep flag

Lets Warm Up

#general#50pt#bases#ascii

If I told you a word started with 0x70 in hexadecimal, what would it start with in ASCII?

picoCTF{p}

Use xxd with -r to get the reverse of the hex representation

echo "70" | xxd -r -p

The Numbers

#cryptography#50pt#a1z26

The numbers... what do they mean?

PICOCTF{THENUMBERSMASON}

Visually obtain numbers in image: 16 9 3 15 3 20 6 { 20 8 5 14 21 13 2 5 18 19 13 1 19 15 14 }

Quick observation (3: C and 9: I) suggests a simple a1z26 cipher.

function decodeA1Z26(ciphertext, alphabet = "abcdefghijklmnopqrstuvwxyz") {
  const parts = ciphertext.split(" ");
  let plaintext = "";
  parts.forEach(part => {
    const letter = alphabet[parseInt(part) - 1];
    plaintext += letter || part;
  });
  return plaintext.toUpperCase();
}

Warmed Up

#general#50pt#bases#bc

What is 0x3D (base 16) in decimal (base 10).

picoCTF{61}

echo "obase=10; ibase=16; 3D" | bc

handy-shellcode

#binary#unsolved#50pt

This program executes any shellcode that you give it. Can you spawn a shell and use that to read the flag.txt? You can find the program in /problems/handy-shellcode_4_037bd47611d842b565cfa1f378bfd8d9 on the shell server. Source.

practice-run-1

#binary#50pt

You're going to need to know how to run programs if you're going to get out of here. Navigate to /problems/practice-run-1_0_62b61488e896645ebff9b6c97d0e775e on the shell server and run this program to receive a flag.

picoCTF{g3t_r3adY_2_r3v3r53}

Simply download and execute with:

./run_this

unzip

#forensics#50pt#unzip

Can you unzip this file and get the flag?

picoCTF{unz1pp1ng_1s_3a5y}

unzip flag.zip
# open image file

vault-door-training

#reverse#50pt

Your mission is to enter Dr. Evil's laboratory and retrieve the blueprints for his Doomsday Project. The laboratory is protected by a series of locked vault doors. Each door is controlled by a computer and requires a password to open. Unfortunately, our undercover agents have not been able to obtain the secret passwords for the vault doors, but one of our junior agents obtained the source code for each vault's computer! You will need to read the source code for each level to figure out what the password is for that vault door. As a warmup, we have created a replica vault in our training facility. The source code for the training vault is here: VaultDoorTraining.java

picoCTF{w4rm1ng_Up_w1tH_jAv4_e57d01a632a}

Read the source code to obtain the password.

13

#cryptography#100pt#rot13

Cryptography can be easy, do you know what ROT13 is? cvpbPGS{abg_gbb_onq_bs_n_ceboyrz}

picoCTF{not_too_bad_of_a_problem}

Read https://en.wikipedia.org/wiki/ROT13

function decodeCaesar(
  ciphertext,
  alphabets = "abcdefghijklmnopqrstuvwxyz",
  shift = 13
) {
  let plaintext = "";
  for (let i = 0; i < ciphertext.length; i++) {
    const cipherChar = ciphertext[i];
    const cipherIndex = alphabets.indexOf(cipherChar);
    let plainIndex = -1;
    if (cipherIndex >= 0) {
      plainIndex = (cipherIndex + shift) % alphabets.length;
    }
    plaintext += plainIndex >= 0 ? alphabets[plainIndex] : cipherChar;
  }
  return plaintext;
}

Bases

#general#100pt#base64

What does this bDNhcm5fdGgzX3IwcDM1 mean? I think it has something to do with bases.

picoCTF{l3arn_th3_r0p35}

Looks like a base64-encoded string. Decode it with:

echo "bDNhcm5fdGgzX3IwcDM1" | base64 -D

Easy1

#cryptography#vigenere

The one time pad can be cryptographically secure, but not when you know the key. Can you solve this? We've given you the encrypted flag, key, and a table to help UFJKXQZQUNB with the key of SOLVECRYPTO. Can you use this table to solve it?.

picoCTF{CRYPTOISFUN}

Read https://en.wikipedia.org/wiki/One-time_pad and use the table to decrypt by finding the plaintext characters via the row (key) by column (ciphertext) intersection.

    A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
   +----------------------------------------------------
A | A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
B | B C D E F G H I J K L M N O P Q R S T U V W X Y Z A
C | C D E F G H I J K L M N O P Q R S T U V W X Y Z A B
D | D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
E | E F G H I J K L M N O P Q R S T U V W X Y Z A B C D
F | F G H I J K L M N O P Q R S T U V W X Y Z A B C D E
G | G H I J K L M N O P Q R S T U V W X Y Z A B C D E F
H | H I J K L M N O P Q R S T U V W X Y Z A B C D E F G
I | I J K L M N O P Q R S T U V W X Y Z A B C D E F G H
J | J K L M N O P Q R S T U V W X Y Z A B C D E F G H I
K | K L M N O P Q R S T U V W X Y Z A B C D E F G H I J
L | L M N O P Q R S T U V W X Y Z A B C D E F G H I J K
M | M N O P Q R S T U V W X Y Z A B C D E F G H I J K L
N | N O P Q R S T U V W X Y Z A B C D E F G H I J K L M
O | O P Q R S T U V W X Y Z A B C D E F G H I J K L M N
P | P Q R S T U V W X Y Z A B C D E F G H I J K L M N O
Q | Q R S T U V W X Y Z A B C D E F G H I J K L M N O P
R | R S T U V W X Y Z A B C D E F G H I J K L M N O P Q
S | S T U V W X Y Z A B C D E F G H I J K L M N O P Q R
T | T U V W X Y Z A B C D E F G H I J K L M N O P Q R S
U | U V W X Y Z A B C D E F G H I J K L M N O P Q R S T
V | V W X Y Z A B C D E F G H I J K L M N O P Q R S T U
W | W X Y Z A B C D E F G H I J K L M N O P Q R S T U V
X | X Y Z A B C D E F G H I J K L M N O P Q R S T U V W
Y | Y Z A B C D E F G H I J K L M N O P Q R S T U V W X
Z | Z A B C D E F G H I J K L M N O P Q R S T U V W X Y

First Grep

#general#100pt#grep

Can you find the flag in file? This would be really tedious to look through manually, something tells me there is a better way. You can also find the file in /problems/first-grep_0_93be1631acf1a93b98cdcc3e7b9fdc52 on the shell server.

picoCTF{grep_is_good_to_find_things_4b2451ea}

grep picoCTF{ file

Overflow 0

#binary#unsolved#100pt

This should be easy. Overflow the correct buffer in this program and get a flag. Its also found in /problems/overflow-0_4_e130f4df1710865981d50f778a8059f7 on the shell server. Source.

Resources

#general#100pt#grep

We put together a bunch of resources to help you out on our website! If you go over there, you might even find a flag! https://picoctf.com/resources (link)

picoCTF{r3source_pag3_f1ag}

curl https://picoctf.com/resources | grep picoCTF{

caesar

#cryptography#100pt#caesar#brute

Decrypt this message (picoCTF{jyvzzpunaolybipjvunfzpthre}). You can find the ciphertext in /problems/caesar_0_22aa542fadadcc37b6ec6037c493ec9f on the shell server.

picoCTF{crossingtherubicongysimakx}

Use the decodeCaesar method in the earlier problems.

function decrypt(ciphertext) {
  const alphabets = "abcdefghijklmnopqrstuvwxyz";
  for (let i = 0; i < alphabets.length; i++) {
    console.log(decodeCaesar(ciphertext, alphabets, i));
  }
}

dont-use-client-side

#web#100pt#curl

Can you break into this super secure portal? https://2019shell1.picoctf.com/problem/12280/ (link) or http://2019shell1.picoctf.com:12280

picoCTF{no_clients_plz_577431}

Study the javascript code and repiece/reorder the flag.

curl https://2019shell1.picoctf.com/problem/12280/

logon

#web#100pt#postman

The factory is hiding things from all of its users. Can you login as logon and find what they've been looking at? https://2019shell1.picoctf.com/problem/49907/ (link) or http://2019shell1.picoctf.co

picoCTF{th3_c0nsp1r4cy_l1v3s_9e21365b}

  • Study the webpage with curl.
  • Nothing interesting in the HTML/JS/CSS except making a POST request using the form (check the action and form fields)
  • Use Postman to make a POST /login with request body (form-data): user:user and password:pwd.
  • We get a response that suggests redirecting us to the route /flag.
  • Check the response headers and cookies and we notice that admin:false is set by default from the server.
  • Navigate to the GET /flag endpoint and receive a clue that we logged in but cannot view the flag.
  • With the earlier knowledge about the server-set default cookie value for admin, change this in the request headers and resend the GET /flag request.

strings it

#general#100pt#strings#grep

Can you find the flag in file without running it? You can also find the file in /problems/strings-it_3_8386a6aa560aecfba03c0c6a550b5c51 on the shell server.

picoCTF{5tRIng5_1T_c7fff9e5}

strings strings | grep picoCTF{

vault-door-1

#reverse#100pt

This vault uses some complicated arrays! I hope you can make sense of it, special agent. The source code for this vault is here: VaultDoor1.java

picoCTF{d35cr4mbl3_tH3_cH4r4cT3r5_51e7fd}

Read and reverse-engineer the code.

what's a net cat?

#general#100pt#nc

Using netcat (nc) is going to be pretty important. Can you connect to 2019shell1.picoctf.com at port 4158 to get the flag?

picoCTF{nEtCat_Mast3ry_700da9c7}

nc 2019shell1.picoctf.com 4158

where are the robots

#web#100pt#robots#curl#grep

Can you find the robots? https://2019shell1.picoctf.com/problem/4159/ (link) or http://2019shell1.picoctf.com:

picoCTF{ca1cu1at1ng_Mach1n3s_a44f7}

Use the hint to arrive to robots.txt via https://en.wikipedia.org/wiki/Robots_exclusion_standard.

curl https://2019shell1.picoctf.com/problem/4159/
curl https://2019shell1.picoctf.com/problem/4159/robots.txt # see disallowed pages
curl https://2019shell1.picoctf.com/problem/4159/a44f7.html
curl https://2019shell1.picoctf.com/problem/4159/a44f7.html | grep picoCTF{

So Meta

#forensics#150pt#strings#grep

Find the flag in this picture. You can also find the file in /problems/so-meta_6_8d7541b8d04bd65a01336fdb8db6db24

picoCTF{s0_m3ta_505fdd8b}

Image provides no visual clues, check the file content with strings and grep.

strings pico_img.png | grep picoCTF{

What Lies Within

#forensics#unsolved#150pt

Theres something in the building. Can you retrieve the flag?

``

extensions

#forensics#150pt#file

This is a really weird text file TXT? Can you find the flag?

picoCTF{now_you_know_about_extensions}

file flag.txt
mv flag.txt flag.png  # open image file for flag

shark on wire 1

#forensics#unsolved#forensics#150pt

We found this packet capture. Recover the flag. You can also find the file in /problems/shark-on-wire-1_0_13d709ec13952807e477ba1b5404e620.

``

Based

#general#200pt#ascii

To get truly 1337, you must understand different data encodings, such as hexadecimal or binary. Can you get the flag from this program to prove you are on the way to becoming 1337? Connect with nc 2019shell1.picoctf.com 31615.

picoCTF{learning_about_converting_values_502ff297}

Use the following script to solve the problem for bases 2, 8, 16.

function getAsciiString(input, base) {
  return input
    .split(" ")
    .map(char => String.fromCharCode(parseInt(char, base)))
    .join("");
}

Client-side-again

Can you break into this super secure portal? https://2019shell1.picoctf.com/problem/47277/ (link) or http://2019shell1.picoctf.com:47277

picoCTF{not_this_again_d29871}

#web#200pt#obfuscation

Get source code and de-obfuscate code by:

  • Replacing 0x* numbers with actual numbers.
  • Rename variables (e.g. getValue).
  • Compute variables that depend on split.
  • Replace getValue(i) with the actual value in data retrieved (note that data array has been sorted).
  • Reverse-engineer the flag in the nested if conditions.
// de-obfuscated code
var data = [
  "29871}",
  "_again_d",
  "this",
  "Password\x20Verified",
  "Incorrect\x20password",
  "getElementById",
  "value",
  "substring",
  "picoCTF{",
  "not_this"
];
(function(dataArr, i) {
  var callback = function(j) {
    while (--j) {
      dataArr["push"](dataArr["shift"]());
    }
  };
  callback(++i);
})(data, 435);
var getValue = function(index) {
  index = index - 0;
  var result = data[index];
  return result;
};
// data = ["getElementById","value","substring","picoCTF{","not_this","29871}","_again_d","this","Password Verified","Incorrect password"]
function verify() {
  checkpass = document.getElementById("pass").value;
  if (checkpass.substring(0, 8) == "picoCTF{") {
    if (checkpass.substring(7, 9) == "{n") {
      if (checkpass.substring(8, 16) == "not_this") {
        if (checkpass.substring(3, 6) == "oCT") {
          if (checkpass.substring(24, 32) == "29871}") {
            if (checkpass.substring(6, 11) == "F{not") {
              if (checkpass.substring(16, 24) == "_again_d") {
                if (checkpass.substring(12, 16) == "this") {
                  alert("Password Verified");
                  // picoCTF{not_this_again_d29871}
                }
              }
            }
          }
        }
      }
    }
  } else {
    alert(getValue("Incorrect password"));
  }
}

First Grep: Part II

#general#200pt#grep

Can you find the flag in /problems/first-grep--part-ii_6_84224d7d745e41d24bde7e7bc7062bbe/files on the shell server? Remember to use grep.

picoCTF{grep_r_to_find_this_5241c61f}

grep -r picoCTF{ .

Flags

#cryptography#200pt

What do the flags mean?

PICOCTF{F1AG5AND5TUFF}

The image looks like a character mapping of visual flags to text characters. One such mapping exists: https://www.dcode.fr/maritime-signals-code.

Mr-Worldwide

#cryptography#200pt

A musician left us a message. What's it mean?

picoCTF{KODIAK_ALASKA}

The clue is in the name of the problem (i.e. worldwide). Take the first letters of cities (KODIAK) and first letters of regions ALASKA).

Open-to-admins

#web#200pt#postman

This secure website allows users to access the flag only if they are admin and if the time is exactly 1400. https://2019shell1.picoctf.com/problem/49858/ (link) or http://2019shell1.picoctf.com:49858

picoCTF{0p3n_t0_adm1n5_effb525e}

  • Check that there's nothing interesting in the HTML/CSS/JS with curl.
  • There is a link that links to /flag.
  • In Postman make a GET /flag request and we are informed we are not an admin nor the correct time.
  • Set admin=True;time=1400 from the problem description.
  • GET /flag now gives the flag.

Tapping

#cryptography#200pt#morsecode

Theres tapping coming in from the wires. What's it saying nc 2019shell1.picoctf.com 45168

PICOCTF{M0RS3C0D31SFUN348887105}

Run the nc on CLI and it looks like Morse code. Decode it with:

function decodeMorseCode(ciphertext) {
  const alphabets = {
    "-----": "0",
    ".----": "1",
    "..---": "2",
    "...--": "3",
    "....-": "4",
    ".....": "5",
    "-....": "6",
    "--...": "7",
    "---..": "8",
    "----.": "9",
    ".-": "a",
    "-...": "b",
    "-.-.": "c",
    "-..": "d",
    ".": "e",
    "..-.": "f",
    "--.": "g",
    "....": "h",
    "..": "i",
    ".---": "j",
    "-.-": "k",
    ".-..": "l",
    "--": "m",
    "-.": "n",
    "---": "o",
    ".--.": "p",
    "--.-": "q",
    ".-.": "r",
    "...": "s",
    "-": "t",
    "..-": "u",
    "...-": "v",
    ".--": "w",
    "-..-": "x",
    "-.--": "y",
    "--..": "z",
    "/": " ",
    "-·-·--": "!",
    "·-·-·-": ".",
    "--··--": ","
  };
  return ciphertext
    .split(" ")
    .map(char => (alphabets[char] ? alphabets[char] : char))
    .join("")
    .toUpperCase();
}

la cifra de

#cryptography#200pt#vigenere

I found this cipher in an old book. Can you figure out what it says? Connect with nc 2019shell1.picoctf.com 37608.

picoCTF{b311a50_0r_v1gn3r3_c1ph3re62e044a}

Connect with nc and see that we have to decode hgqqpohzCZK{m311a50_0x_a1rn3x3_h1ah3xj62p044a}

The ciphertext seems to preserve the character size of each word, suggesting a Vigenere cipher. Use an online tool https://www.guballa.de/vigenere-solver as suggested by the hint to crack this and capture the flag.

picobrowser

#web#200pt#postman

This website can be rendered only by picobrowser, go and catch the flag! https://2019shell1.picoctf.com/problem/21851/ (link) or http://2019shell1.picoctf.com:2185

picoCTF{p1c0_s3cr3t_ag3nt_3e1c0ea2}

  • Use Postman to make a GET request.
  • Study the HTML and see that there is a link to /flag.
  • Use Postman and make a request to GET /flag.
  • The webpage response suggests that we are PostmanRuntime/7.20.1 and not picobrowser.
  • Study the request headers and notice that User-Agent should be changed from PostmanRuntime/7.20.1 to picobrowser.
  • Resend the GET /flag request.

plumbing

#general#200pt#nc#grep

Sometimes you need to handle process data outside of a file. Can you find a way to keep the output from this program and search for the flag? Connect to 2019shell1.picoctf.com 63345

picoCTF{digital_plumb3r_4e7a5813}

As suggested, we should probably pipe this through grep

nc 2019shell1.picoctf.com 63345 | grep picoCTF{

rsa-pop-quiz

#cryptography#unsolved#200pt

Class, take your seats! It's PRIME-time for a quiz... nc 2019shell1.picoctf.com 53028

``

Learn how RSA works on https://simple.wikipedia.org/wiki/RSA_algorithm. Have the following scripts and a prime checker handy:

# scripts are done in Python to handle larger numbers
def n(p, q):
  return p * q

def q(n, p):
  return n / p

def t(p, q):
  return (p - 1) * (q - 1)

def c(m, e, n):
  return pow(m, e, n)
  • Problem 1:
    • Y: Both p, q are primes.
    • n(76753, 60413) = 4636878989
  • Problem 2:
    • Y: Both p n/p are primes.
    • q(5051846941, 54269) = 93089
  • Problem 3:
    • N: n is divisble by e.
  • Problem 4:
    • Y: Both p, q are primes.
    • t(12611, 66347) = 836623060
  • Problem 5:
    • Y: m is smaller than n.
    • c(6357294171489311547190987615544575133581967886499484091352661406414044440475205342882841236357665973431462491355089413710392273380203038793241564304774271529108729717, 3, 29129463609326322559521123136222078780585451208149138547799121083622333250646678767769126248182207478527881025116332742616201890576280859777513414460842754045651093593251726785499360828237897586278068419875517543013545369871704159718105354690802726645710699029936754265654381929650494383622583174075805797766685192325859982797796060391271817578087472948205626257717479858369754502615173773514087437504532994142632207906501079835037052797306690891600559321673928943158514646572885986881016569647357891598545880304236145548059520898133142087545369179876065657214225826997676844000054327141666320553082128424707948750331) = 256931246631782714357241556582441991993437399854161372646318659020994329843524306570818293602492485385337029697819837182169818816821461486018802894936801257629375428544752970630870631166355711254848465862207765051226282541748174535990314552471546936536330397892907207943448897073772015986097770443616540466471245438117157152783246654401668267323136450122287983612851171545784168132230208726238881861407976917850248110805724300421712827401063963117423718797887144760360749619552577176382615108244813
  • Problem 6:
    • N: Not possible to produce plaintext m with just information on the ciphertext c and public key (n, e).
  • Problem 7:
    • Y: q and p are primes.
    • Unsolved
  • Problem 8:
    • Unsolved

vault-door-3

#reverse#unsolved#200pt

This vault uses for-loops and byte arrays. The source code for this vault is here: VaultDoor3.java

``

whats-the-difference

#general#200pt#cmp#awk#tr#ascii

Can you spot the difference? kitters cattos. They are also available at /problems/whats-the-difference_0_00862749a2aeb45993f36cc9cf98a47a on the shell server

picoCTF{th3yr3_a5_d1ff3r3nt_4s_bu773r_4nd_j311y_aslkjfdsalkfslkflkjdsfdszmz10548}

Compare the two files using cmp. Note that the third column looks like ASCII codes. Use the getAsciiString method in earlier problems to get the flag.

cmp kitters.jpg cattos.jpg -l
cmp kitters.jpg cattos.jpg -l | awk '{print $3}' | tr '\n' ' '

where-is-the-file

#general#200pt

I've used a super secret mind trick to hide this file. Maybe something lies in /problems/where-is-the-file_3_19c1a7766ac2747c446eb9666a9b4fb4.

``

WhitePages

#forensics#250pt#xxd#awk#sed#ascii

I stopped using YellowPages and moved onto WhitePages... but the page they gave me is all blank!

picoCTF{not_all_spaces_are_created_equal_c167040c738e8bcae2109ef4be5960b1}

file whitepages.txt  # non-empty
xxd whitepages.txt  # only white-space characters 20 and e28083, try representing these as binary
xxd whitepages.txt | awk '{printf $2$3$4$5$6$7$8$9}' | sed s/e28083/1/g | sed s/20/0/g  # first possible binary string (bstring1)
xxd whitepages.txt | awk '{printf $2$3$4$5$6$7$8$9}' | sed s/e28083/0/g | sed s/20/1/g  # second possible binary string (bstring2)

We should group the binary string by bits. Let's use a general delimitate function below and call the getAsciiString method in earlier problems

function delimitate(input, width = 8, delimiter = " ") {
  let result = "";
  for (let i = 0; i < input.length; i++) {
    if (i > 0 && i % width == 0) {
      result += delimiter;
    }
    result += input[i];
  }
  return result;
}

getAsciiString(delimitate(bstring1), 2); // gibberish
getAsciiString(delimitate(bstring2), 2); // the flag shows up!

c0rrupt

#forensics#unsolved#250pt

We found this file. Recover the flag. You can also find the file in /problems/c0rrupt_0_1fcad1344c25a122a00721e4af86de13.

``

like1000

#forensics#250pt#tar

This .tar file got tarred alot. Also available at /problems/like1000_0_369bbdba2af17750ddf10cc415672f1c.

picoCTF{l0t5_0f_TAR5}

Scripting this in Python is easier than JS using the tarfile module.

import tarfile

def untar(tar_file):
    tf = tarfile.open(tar_file)
    tf.extractall()


def run():
    """Untars a tarfile recursively"""
    tar_count = 1000
    while tar_count > 0:
        tar_file = './{}.tar'.format(tar_count)
        print('Untarring file {}...'.format(tar_file))
        untar(tar_file)
        tar_count -= 1

run()

m00nwalk

#forensics#unsolved#250pt

Decode this message from the moon. You can also find the file in /problems/m00nwalk_5_72c1b4e13cc7ddd43d7fb3b0ae86afef.

``

Read about the WAV/RIFF format: https://www.isip.piconepress.com/projects/speech/software/tutorials/production/fundamentals/v1.0/section_02/s02_01_p05.html

We are interested in the data of the file. Use xxd and seek to 45 to obtain the data.

xxd -s 45 message.wav > data

Irish-Name-Repo 1

#web#300pt#sql

There is a website running at https://2019shell1.picoctf.com/problem/37868/ (link) or http://2019shell1.picoctf.com:37868. Do you think you can log us in? Try to see if you can login!

picoCTF{s0m3_SQL_a57b0b1d}

The website does not provide anything useful aside from a hint in the /support page where someone complains about a SQL Error. Together with the problem hint, let's try the simple SQL injections:

  • '--: Nothing happens, which means the filter conditions are applied before the injection.
  • 'OR 1=1--: We successfully logged in :)

waves over lambda

#cryptography#300pt#frequency#grep#sed

We made alot of substitutions to encrypt this. Can you decrypt it? Connect with nc 2019shell1.picoctf.com 45185

picoCTF{frequency_is_c_over_lambda_mupgpennod}

Store a persisted file to decrypt via nc 2019shell1.picoctf.com 45185 > substitutions.txt

hfigffb sl ijfvf gul, ul o juef uqvfuwn luow lcdfgjfvf, ijf hcbw cx ijf lfu. hflowfl jcqwobt csv jfuvil ictfijfv ijvcstj qcbt yfvocwl cx lfyuvuiocb, oi juw ijf fxxfpi cx duaobt sl icqfvubi cx fupj cijfv'l nuvblubw fefb pcbeopiocbl. ijf qugnfvijf hfli cx cqw xfqqcgljuw, hfpuslf cx jol dubn nfuvl ubw dubn eovisfl, ijf cbqn psljocb cb wfpa, ubw gul qnobt cb ijf cbqn vst. ijf uppcsbiubi juw hvcstji csi uqvfuwn u hcm cx wcdobcfl, ubw gul icnobt uvpjoifpisvuqqn goij ijf hcbfl. duvqcg lui pvcll-qfttfw votji uxi, qfubobt utuobli ijf dokkfb-duli. jf juw lsbafb pjffal, u nfqqcg pcdyqfmocb, u livuotji hupa, ub ulpfiop ulyfpi, ubw, goij jol uvdl wvcyyfw, ijf yuqdl cx jubwl csiguvwl, vflfdhqfw ub owcq. ijf wovfpicv, luiolxofw ijf ubpjcv juw tccw jcqw, duwf jol gun uxi ubw lui wcgb udcbtli sl. gf fmpjubtfw u xfg gcvwl qukoqn. uxifvguvwl ijfvf gul loqfbpf cb hcuvw ijf nupji. xcv lcdf vfulcb cv cijfv gf wow bci hftob ijui tudf cx wcdobcfl. gf xfqi dfwoiuioef, ubw xoi xcv bcijobt hsi yqupow liuvobt. ijf wun gul fbwobt ob u lfvfboin cx lioqq ubw fmzsoloif hvoqqoubpf. ijf guifv ljcbf yupoxopuqqn; ijf lan, goijcsi u lyfpa, gul u hfbotb oddfbloin cx sbliuobfw qotji; ijf efvn doli cb ijf fllfm duvlj gul qoaf u tuskn ubw vuwoubi xuhvop, jsbt xvcd ijf gccwfw volfl obqubw, ubw wvuyobt ijf qcg ljcvfl ob wouyjubcsl xcqwl. cbqn ijf tqccd ic ijf gfli, hvccwobt cefv ijf syyfv vfupjfl, hfpudf dcvf lcdhvf fefvn dobsif, ul ox ubtfvfw hn ijf uyyvcupj cx ijf lsb.

Use cat and grep to visually observe the file, apply frequencies based on the analyzer results, and make relevant substitutions with sed:

  • ijf -> THE
  • v -> R: exists in THEvE and THv cannot be TH[sm]
  • c -> O: exists in Tc and is a valid first character to many digraphs c*
  • e -> V: exists in OeER
  • x -> F: exists in many Ox occurrences
  • o -> I: exists as a single character and in relevant bigrams oF, oT
  • l -> S: exists in relevant bigrams Il and trigrams HIl
  • n -> Y, s -> U, q -> L, u -> A, t -> G: purely because we know HERE IS n0sR Fqut now implies HERE IS YOUR FLAG :P
  • w -> D: based on ALREAwY and SAIw
  • y -> P: based on yERIODS, DROyyED, and UyyER
  • h -> B: based on hESIDES and hUT
  • b -> N: based on HOLDIbG and SEPARATIOb
  • m -> x: based on BOm, EmxUISITE, ESSEm
  • g -> W: based on BETgEEN and gAS
  • p -> C: based on EFFEpT and EApH
  • d -> M: based on dORE, dINUTE
  • a -> K: based on BACa, DECa, LIaE
  • z -> Q: based on FREzUENCY
  • k -> Z: based on LAkILY

The final script will give us the flag!

cat substitutions.txt | sed 's/i/T/g; s/j/H/g; s/f/E/g; s/v/R/g; s/c/O/g; s/e/V/g; s/x/F/g; s/o/I/g; s/l/S/g; s/n/Y/g; s/s/U/g; s/q/L/g; s/u/A/g; s/t/G/g; s/w/D/g; s/y/P/g; s/h/B/g; s/b/N/g; s/m/X/g; s/g/W/g; s/p/C/g; s/d/M/g; s/a/K/g; s/z/Q/g; s/k/Z/g;'
-------------------------------------------------------------------------------
CONGRATS HERE IS YOUR FLAG - FREQUENCY_IS_C_OVER_LAMBDA_MUPGPENNOD
-------------------------------------------------------------------------------
BETWEEN US THERE WAS, AS I HAVE ALREADY SAID SOMEWHERE, THE BOND OF THE SEA. BESIDES HOLDING OUR HEARTS TOGETHER THROUGH LONG PERIODS OF SEPARATION, IT HAD THE EFFECT OF MAKING US TOLERANT OF EACH OTHER'S YARNSAND EVEN CONVICTIONS. THE LAWYERTHE BEST OF OLD FELLOWSHAD, BECAUSE OF HIS MANY YEARS AND MANY VIRTUES, THE ONLY CUSHION ON DECK, AND WAS LYING ON THE ONLY RUG. THE ACCOUNTANT HAD BROUGHT OUT ALREADY A BOX OF DOMINOES, AND WAS TOYING ARCHITECTURALLY WITH THE BONES. MARLOW SAT CROSS-LEGGED RIGHT AFT, LEANING AGAINST THE MIZZEN-MAST. HE HAD SUNKEN CHEEKS, A YELLOW COMPLEXION, A STRAIGHT BACK, AN ASCETIC ASPECT, AND, WITH HIS ARMS DROPPED, THE PALMS OF HANDS OUTWARDS, RESEMBLED AN IDOL. THE DIRECTOR, SATISFIED THE ANCHOR HAD GOOD HOLD, MADE HIS WAY AFT AND SAT DOWN AMONGST US. WE EXCHANGED A FEW WORDS LAZILY. AFTERWARDS THERE WAS SILENCE ON BOARD THE YACHT. FOR SOME REASON OR OTHER WE DID NOT BEGIN THAT GAME OF DOMINOES. WE FELT MEDITATIVE, AND FIT FOR NOTHING BUT PLACID STARING. THE DAY WAS ENDING IN A SERENITY OF STILL AND EXQUISITE BRILLIANCE. THE WATER SHONE PACIFICALLY; THE SKY, WITHOUT A SPECK, WAS A BENIGN IMMENSITY OF UNSTAINED LIGHT; THE VERY MIST ON THE ESSEX MARSH WAS LIKE A GAUZY AND RADIANT FABRIC, HUNG FROM THE WOODED RISES INLAND, AND DRAPING THE LOW SHORES IN DIAPHANOUS FOLDS. ONLY THE GLOOM TO THE WEST, BROODING OVER THE UPPER REACHES, BECAME MORE SOMBRE EVERY MINUTE, AS IF ANGERED BY THE APPROACH OF THE SUN.

Irish-Name-Repo 2

#web#350pt#curl#sql

There is a website running at https://2019shell1.picoctf.com/problem/7411/ (link). Someone has bypassed the login before, and now it's being strengthened. Try to see if you can still login! or http://2019shell1.picoctf.com:7411

picoCTF{m0R3_SQL_plz_c1c3dff7}

  • Similar to the Irish-Name-Repo 1 problem, try 'OR 1=1-- in the username field.
  • We see that the developer has fixed the issue and detected our SQL injection, and threw us a SQLi detected. message :(
  • We notice that we can send debug=1 in the request body and it will output us the SQL error!
  • Build the correct filter condition by injecting the at the name field and before the password field to capture the flag.
  • Successfully logged in :)
curl https://2019shell1.picoctf.com/problem/7411/login.php -d "username='admin--&debug=1"
curl https://2019shell1.picoctf.com/problem/7411/login.php -d "username=admin'--&debug=1"

Empire1 #400pt

#web#400pt#unsolved

Psst, Agent 513, now that you're an employee of Evil Empire Co., try to get their secrets off the company website. https://2019shell1.picoctf.com/problem/4155/ (link) Can you first find the secret code they assigned to you? or http://2019shell1.picoctf.com:4155

``

Irish-Name-Repo 3

#web#400pt#unsolved

There is a secure website running at https://2019shell1.picoctf.com/problem/45112/ (link) or http://2019shell1.picoctf.com:45112. Try to see if you can login as admin!

``

JaWT Scratchpad

#web#400pt#unsolved

Check the admin scratchpad! https://2019shell1.picoctf.com/problem/12283/ or http://2019shell1.picoctf.com:12283

``

Java Script Kiddie

#web#400pt#unsolved

The image link appears broken... https://2019shell1.picoctf.com/problem/57738 or http://2019shell1.picoctf.com:57738

``

cereal hacker 1

#web#400pt#unsolved

Login as admin. https://2019shell1.picoctf.com/problem/21885/ or http://2019shell1.picoctf.com:21885

``

Ghost_Diary

#binary#500pt#unsolved

Try writing in this ghost diary. Its also found in /problems/ghost-diary_6_5a9aa6b551e71294dfdc06646d2d7104 on the shell server.

``