# __X-MAS CTF 2018__
## _Santa's Secret B(i)smuth_
**Category:** | **Points:** | **Writeup Author**
--- | --- | ---
Crypto | 486 | MiKHalyCH
> Samba's Union have found some of Santa's ancient and most valuable secrets. Luckily, they are encrypted, even so, you must be quick enough to retrieve them before the Sambas do!
>Sadly, Santa does not remember the encryption scheme, he does remember though that it had something to do with bismuth, or was it something else...?
According to crypto tasks experience it was realy easy to understand that it is some secret sharing system. But it took a lot of time to find the right name of it.
One realy good step was googling [secret sharing smuth](http://lmgtfy.com/?q=secret+sharing+smuth).
This is [Asmuth-Bloom's threshold secret sharing scheme](http://cryptowiki.net/index.php?title=Asmuth-Bloom_scheme):
common_part = p
Secret = [(I_i, p_i) for i in range(10)]
[Solution](solver.py) can be easily found by [Chinese remainder theorem](https://en.wikipedia.org/wiki/Chinese_remainder_theorem).