Crypto
The year is 20XX. ångstromCTF only has pwn challenges, and the winner is solely determined by who can establish a socket connection first. In the data remnants of an ancient hard disk, we've recovered a string of letters and digits. The only clue is the etching on the disk's surface: Paillier.
Author: defund
n: 99157116611790833573985267443453374677300242114595736901854871276546481648883
g: 99157116611790833573985267443453374677300242114595736901854871276546481648884
c: 2433283484328067719826123652791700922735828879195114568755579061061723786565164234075183183699826399799223318790711772573290060335232568738641793425546869
Since n is factorised at factordb.com
p = 310013024566643256138761337388255591613
q = 319848228152346890121384041219876391791
We simply need to decrypt it. The equation is on the Wikipedia page
https://en.wikipedia.org/wiki/Paillier_cryptosystem#Decryption
I implemented Paillier decryption in Ruby script.
$ ruby paillier_solve.rb
actf{crypto_lives}
actf{crypto_lives}