#Sekai_CTF_2022
import hashlib
from os import urandom
from flag import FLAG
def gen_pubkey(secret: bytes, hasher=hashlib.sha512) -> list:
def hash(m): return hasher(m).digest()
state = hash(secret)
pubkey = []
for _ in range(len(hash(b'0')) * 4):
pubkey.append(int.from_bytes(state, 'big'))
state = hash(state)
return pubkey
def happiness(x: int) -> int:
return x - sum((x >> i) for i in range(1, x.bit_length()))
def encode_message(message: bytes, segment_len: int) -> list:
message += bytes(segment_len - len(message) % (segment_len))
encoded = []
for i in range(0, len(message), segment_len):
block = message[i:i + segment_len]
encoded.append(int.from_bytes(block, 'big'))
return encoded
def encrypt(pubkey: list, message: bytes) -> list:
encrypted_blocks = []
for block_int in encode_message(message, len(pubkey) // 4):
encrypted_blocks.append([happiness(i & block_int) for i in pubkey])
return encrypted_blocks
secret = urandom(16)
A = gen_pubkey(secret, hashlib.sha256)
enc = encrypt(A, FLAG)
print(secret.hex())
print(enc)
