README.md

ctfd_user-challange-dynamic-flag

CTFd Dynamic flag by user ID & chalange ID

Description

Code modification allows you to generate dynamic flags by user id and challange id.

Instruction

1. clone CTFd GitHub repository
2. change directory to CTFd cd CTFd
3. in file CTFd/api/v1/challenges.py replace line (2x)

status, message = chal_class.attempt(challenge, request)

to line

status, message = chal_class.attempt(challenge, request, user)

4. in file CTFd/plugins/challenges/__init__.py

• replace line

def attempt(cls, challenge, request):

to line

def attempt(cls, challenge, request, user):

• add block of code after flags = Flags.query.filter_by(challenge_id=challenge.id).all()

        import hashlib
        string_1=b"String1"
        string_2=b"String2"
        string_3=b"String3"
        user_id=int(user.id)
        challange_id=challenge.id
        flag_hash=hashlib.sha256(string_1+int(user_id).to_bytes(4, byteorder='big')+string_2+int(challange_id).to_bytes(4, byteorder='big')+string_3).hexdigest()
        if submission=="flag{"+flag_hash+"}":
            return True, "Correct"

Script

You can just execute automated script

Generate flag

After this steps you don't have to add flag to the challange. You can just generate and add flag to your CTF environment. It will be validated for the specific:

• Strings (3x)
• user id
• challange id