# Amsterdam Writeup
### Crypto CTF 2020 - Crypto 55 - 96 solves
> Is it normal to have such [encoding](./amsterdam_9e529fa12c74f176f23ca19ea4d9aa5fe2e98e6e.txz)?
#### Encryption logic
Flag was encoded to bit contained list, and encoded again by adding binomai coefficients. 
#### Exploit
Write `decode()` function which simply reverses encryption logic. Used sage for faster calculation of binomials.
I get flag:
```CCTF{With_Re3p3ct_for_Sch4lkwijk_dec3nt_Encoding!}```
Exploit code: [solve.sage](solve.sage) with [config.py](config.py)