Kaiwen He kevin-he-01

Sprint — Google CTF 2020

Author: Kevin He
Team: 3PAC
Challenge Category: Reversing
Points: 173
Attachments: sprint.elf

Sprint faster than this binary!

Abstract

Chunk Norris — Google CTF 2020

Author: Kevin He
Team: 3PAC
Challenge Category: Crypto
Points: 98
Attachments: See challenge.py and output.txt in this Gist.

Chunk Norris is black belt in fast random number generation.

Start off by examining the code for challenge.py. It uses RSA — a modern public key cryptography algorithm — to encrypt the flag. The idea behind public key cryptography is that given the public key, everyone can encrypt plaintext messages, but only the party who possesses the secret private key can decrypt the ciphertext back into plaintext. In this challenge, only the public key is given, and it consists of the modulo n — a product of 2 large prime numbers — and the exponent e. However, the security of RSA heavily depends on the fact that its public key modulo n cannot be factored into its constituent primes p and q. Once p and q are known, the private key `d

	Will:
	https://avatars.githubusercontent.com/u/59716405?v=4

	Bill:
	https://lh3.googleusercontent.com/pw/AM-JKLXQ2ix4dg-PzLrPOSMOOy6M3PSUrijov9jCLXs4IGSTwN73B4kr-F6Nti_4KsiUU8LzDSGPSWNKnFdKIPqCQ2dFTRbARsW76pevHPBzc51nceZDZrMPmDfAYyI4XNOnPrZarGlLLUZW9wal6j-z9uA6WQ=w854-h924-no?authuser=0

	Kevin:
	https://avatars.githubusercontent.com/u/32375681?v=4

	Bill mocking:

	from pwn import *

	r = remote('gelcode.hsc.tf', 1337)

	# Run mkshellcode.py to generate this file
	with open('sc.in', 'rb') as scf:
	r.send(scf.read())

	r.interactive()