tl;dr

• Reverse bytearray to recover matrix cflag.
• Use first element of matrix to recover e (bruteforce &iroot)
• Reduce the flag to finite field of a 32-bit prime, solve for each character.

Writeup from Junior 35c3CTF’18

Junior 35c3CTF 2018: pretty-linear

Category: Crypto
Challenge Points: 158
Solves: 28

Description:

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The NSA gave us these packets, they said it should be just enough to break this crypto.

surveillance.pcap server.py

Difficulty estimate: Medium-Hard