niteCTF 2021, Rabin to the Rescue Writeup

Description

  1. We have some cryptosystem that looks like an RSA, but it is not an RSA.
  2. We don’t know any parameters of the cryptosystem.
  3. We have an encryption oracle
  4. We have an encrypted flag

Solution

awawa@awawa-pc:~/Documents/CTF/niteCTF$ python3 rabin_solution.py  
[+] Opening connection to rabin.challenge.cryptonite.team on port 1337: Done
Obtaining x
Obtaining y
Calculating modulus
Obtaining flag
Factoring modulus
Decrypting
b'\x84\x14hMnf\xc7\xda\x12:\xac\xb7_\xdd\xe7\x06\xae\xc0\xf8\x99\x1a\xbbX\xf57\xc5\x9b\xde\xbc\x90&$\xfeq\x9d\x87\\U\xd4\xba\xcd2\xd0z\xe0\x06\td\x9e\xb4\xd1?\xe4\x06\x04\x84\x0e:\xec\x06\x19g}\x1c'
b'nite{r3p34t3d_r461n_3ncrypt10n_l1tr4lly_k1ll5_3d6f4adc5e}'
b'KQ\xbe0k\xdcCH\xa9u\xb6\x1eC\x1b\x9dk\r\xa8L\xea\xfa\x9f\x91\xa4\xf3\xbe\x88\xf3\xb44\x8aq\xe2t\xf2\x88\xef\\u\xae\xecI[\xd1\xd9\xb2\xc3&\x8e\x83\xc6;\xc7q`{\xdc\x8b\x8c\xcb\xdb=A\x8b'
b'8\xc2\xaa\x1d\x02\x8a\x84\xff\xd29\\\x14\x8e\xf5\xb9\xce\xd5\x8c\xdf\x12\x7f\x8d\xfb\x86uur\x1ev\xbf\x0e,\x8cp\xdc.\xdbX\xcb=U[\xa9\x15r\xcc\xa5\xa9A\x9dw9{\xc8\x08>\x97\xe3\xc0\x9e\xa1_\xa1\x0e'
awawa@awawa-pc:~/Documents/CTF/niteCTF$

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