Introduction

In this task, we are given a file vals.txt which contains the values of N, e, and c.

Explanatory notes
(N, e) is the public key
c is the ciphertext

Solving

This problem can be easily solved by integer factorization, explained more here. I used simple tool called X-RSA.

We can simply use the first attack for c, n, e and get the flag. This tools uses http://factordb.com/ under the hood but we can also compute it on our own machine using cado-nfs :D

utflag{just_send_plaintext}