Tan

Tan

• Category: Crypto
• Score: 418/500
• Solves: 32

Description

tan(x) is a broken hash function in terms of collision resistance and second preimage resistance. But you surely can't find the preimage of tan(flag), right?

Solution

Let the flag be $m$ and the output be $t$, then $\arctan(t)+k\pi \approx m$ with some precision loss. Note that $m$ is an integer, so we can use LLL to minimize the decimal part of $\arctan(t)+k\pi$ then $m$ will magically appear.