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README.md

Challenge: credstuff

Category: Cryptography

Point Value: 100

Author: WILL HONG / LT 'SYREAL' JONES


Description:

We found a leak of a blackmarket website's login credentials. Can you find the password of the user 'cultiris' and successfully decrypt it? Download the leak here1. local The first user in usernames.txt corresponds to the first password in passwords.txt. The second user corresponds to the second password, and so on.

Write-Up:

Let's start by getting the leak and extracting it:

wget https://artifacts.picoctf.net/c/534/leak.tar
tar -xf leak.tar

Now we have a new folder in our working directory, with two files in it.

leak/passwords.txt
leak/usernames.txt

Opening them up we see single entries per line in both, with the passwords.txt looking like hashes.

usernames.txt

engineerrissoles
icebunt
fruitfultry
celebritypentathlon
galoshesopinion
favorboeing
...

passwords.txt

CMPTmLrgfYCexGzJu6TbdGwZa
GK73YKE2XD2TEnvJeHRBdfpt2
UukmEk5NCPGUSfs5tGWPK26gG
kaL36YJtvZMdbTdLuQRx84t85
K9gzHFpwF2azPayAUSrcL8fJ9
rYrtRbkHvJzPmDwzD6gSDbAE3
...

Knowing this I created a solve.py script to iterate through the files and search for our username:password hash combo.

usernameFile = './leak/usernames.txt'
passwordFile = './leak/passwords.txt'

userToFind = 'cultiris'

# open the files
un = open(usernameFile, 'r')
pw = open(passwordFile, 'r')

unList = un.readlines()
pwList = pw.readlines()

for x in range(len(unList)):
  if(userToFind in unList[x]):
    print(unList[x] + ' : ' + pwList[x])



un.close()
pw.close()

Running the script we get this Output:

└─$ python3 ./solve.py
cultiris
 : cvpbPGS{P7e1S_54I35_71Z3}

Now that doesnt looks like a password hash, and appeared to be in the format of our picoCTF{} flag. Because of previous challenges I've done I know that 'cvpbPGS' is 'picoCTF' put throught a ROT13 cypher. So using rot13.com, I plugged in the cyphered flag and got this result:

picoCTF{C7r1F_54V35_71M3}

FLAG:

picoCTF{C7r1F_54V35_71M3}

Footnotes

  1. Included links to the source code may be out of date as they were what I recorded during the competition, and may be different now. ↩