# find_hash.py — find a flag that passes the checksum
import struct

def compute_hash(flag_bytes):
    eax = 0x65
    for b in flag_bytes:
        ecx = eax & 0xFFFFFFFF
        edx = eax & 0xFF  # dl only
        ecx = (ecx << 6) & 0xFFFFFFFF
        edx = (edx >> 6) & 0xFF
        eax = (eax + ecx) & 0xFFFFFFFF
        eax = (eax + edx) & 0xFFFFFFFF
        eax ^= b
    return eax & 0xFF

prefix = b"CTF{th1s_"
suffix = b"}"
# 64 bytes total: 9 prefix + 54 middle + 1 suffix
# Try different last middle byte
for last in range(0x21, 0x7F):
    middle = b"A" * 53 + bytes([last])
    flag = prefix + middle + suffix
    assert len(flag) == 64
    h = compute_hash(flag)
    if h == 0x0C:
        print(f"Found: {flag.decode()}")
        print(f"Hash: 0x{h:02x}")
        break