Credstuff

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 here.

Opening up usernames.txt and passwords.txt in Pycharm, we see cultiris is on line 378 of usernames.txt so we go to line 378 of passwords.txt and find an encrypted password:

cvpbPGS{P7e1S_54I35_71Z3}

The {} are in place, implying that it's some sort of transposition cipher for the letters. We've done it numerous times, but we try a caesar cipher decode:

from string import ascii_lowercase, ascii_uppercase

enc_flag = 'cvpbPGS{P7e1S_54I35_71Z3}'

for shift in range(26):
    flag = ''

    for c in enc_flag:
        if c in ascii_lowercase:
            flag += ascii_lowercase[(ascii_lowercase.index(c) + shift) % 26]
        elif c in ascii_uppercase:
            flag += ascii_uppercase[(ascii_uppercase.index(c) + shift) % 26]
        else:
            flag += c

    print(flag)

# picoCTF{C7r1F_54V35_71M3}

In fact the shift is 13, so it's just a ROT13.