Notes

import requests
import json
from datetime import datetime, timedelta
from Crypto.Hash import SHA256
from Crypto.PublicKey import ECC
from Crypto.Signature import DSS

# URLs for the time-server and content-server
TIME_SERVER_URL = 'https://web-one-day-one-letter-time-lz56g6.wanictf.org'
CONTENT_SERVER_URL = 'https://web-one-day-one-letter-content-lz56g6.wanictf.org'

def get_pubkey():
response = requests.get(f'{TIME_SERVER_URL}/pubkey')
return ECC.import_key(response.text)

def get_signed_timestamp():
response = requests.get(TIME_SERVER_URL)
data = response.json()
return data['timestamp'], data['signature']

def get_flag_hint(timestamp, signature):
data = {
'timestamp': timestamp,
'signature': signature,
'timeserver': 'web-one-day-one-letter-time-lz56g6.wanictf.org'
}
headers = {'Content-Type': 'application/json'}
response = requests.post(CONTENT_SERVER_URL, headers=headers, data=json.dumps(data))
return response.text

def main():
pubkey = get_pubkey()
base_time = datetime(1970, 1, 1) # UNIX epoch

for i in range(12):
target_day = i * (60*60*24) # Calculate the target day in seconds since epoch
timestamp = int(base_time.timestamp()) + target_day

# Request the signed timestamp from the time-server
signed_timestamp, signature = get_signed_timestamp()

# Replace the signed timestamp with our calculated timestamp
signed_timestamp = str(timestamp)
h = SHA256.new(signed_timestamp.encode('utf-8'))
verifier = DSS.new(pubkey, 'fips-186-3')

# Verify the signature
if verifier.verify(h, bytes.fromhex(signature)):
# Send the timestamp and signature to the content-server
result = get_flag_hint(signed_timestamp, signature)
print(f"Timestamp: {signed_timestamp}, Flag hint: {result}")
else:
print(f"Signature verification failed for timestamp {signed_timestamp}")

if __name__ == "__main__":
main()