Digestive

Help

This page offers a convenient way for you to interact with the "Digestive" challenge functions. You can also use GET requests to send and receive data directly from the listed routes/endpoints if you wish. For more information see the FAQ.

Your aim is to recover the FLAG value. Once you have have it, submit it on the ECC challenge page.

Source

import hashlib
import json
import string
from ecdsa import SigningKey

SK = SigningKey.generate() # uses NIST192p
VK = SK.verifying_key


class HashFunc:
    def __init__(self, data):
        self.data = data

    def digest(self):
        # return hashlib.sha256(data).digest()
        return self.data



@chal.route('/digestive/sign/<username>/')
def sign(username):
    sanitized_username = "".join(a for a in username if a in string.ascii_lowercase)
    msg = json.dumps({"admin": False, "username": sanitized_username})
    signature = SK.sign(
        msg.encode(),
        hashfunc=HashFunc,
    )

    # remember to remove the backslashes from the double-encoded JSON
    return {"msg": msg, "signature": signature.hex()}


@chal.route('/digestive/verify/<msg>/<signature>/')
def verify(msg, signature):
    try:
        VK.verify(
            bytes.fromhex(signature),
            msg.encode(),
            hashfunc=HashFunc,
        )
    except:
        return {"error": "Signature verification failed"}

    verified_input = json.loads(msg)
    if "admin" in verified_input and verified_input["admin"] == True:
        return {"flag": FLAG}
    else:
        return {"error": f"{verified_input['username']} is not an admin"}