Computer Science and Offensive Security Knowledge Base

The Genchumen Knowledge-Base This project seeks to serve as a source for quick information to aid in solving Capture-The-Flag challenges, although it could very well serve as a general launching point for learning about cybersecurity.

Modulo Function Written as % or $\mod x$ The modulo function is the equivalent of taking the remainder of two numbers. Modular Equivalence A common way to express modular equivalence by a number $n$ is $x\equiv y\pmod n$ Greatest Common Divisor Written as $gcd(x,y)$ The greatest common divisor of two or more integers is the largest positive integer that divides each of the integers. Least Common Multiple Written as $lcm(x,y)$ Euler's Totient Function A....

Public-Key Cryptosystems Okamoto-Uchiyama The Okamoto-Uchiyama cryptosystem is homomorphic and malleable. cryptosystem. Choose random primes $p$ and $q$ Compute $n=p^2q$ Choose $g\in{2\ldots n-1}$ such that $g^{p-1} \not\equiv 1\bmod p^2$ Compute $h=g^n\bmod n$ Encryption Choose message $m<p$ Chose integer $r\in{1\ldots n-1}$ at random Compute ciphertext $c=g^mh^r\bmod n$ Decryption Define $L(x)=\frac{x-1}{p}$ $m=\frac{L(c^{p-1}\bmod p^2)}{L(g^{p-1}\bmod p^2)}\bmod p$ RSA Rivest-Shamir-Adleman Choose random primes $p$ and $q$ Compute $n=pq$ Compute [Euler's totient](algo....

Wired Equivalent Privacy WEP uses the Rivest Cipher 4 algorithm for packet encryption and the 32-bit version of the Cyclic Rendundancy Check to verify packet integrity. Fluhrer, Mantin, Shamir Attack The FMS attack exploits WEP's use of weak initialization vectors (only 24 bits) with RC4. Passive Initialization Vector Capture If a target network has enough traffic, an attacker can passively sniff packets until identical IV's are captured. Packet Injection Packet injection can be used to generate more traffic in a WEP network, generating more IV's to capture....

Image Coordinate Identification The goal of image coordinate identification questions is to find where an image was taken and/or other details surrounding the circumstances of the image. Reverse Image search Reverse image searching is one of the most bang-for-your-buck techniques in image coordinate identification. It also offers a launching point to find search terms that describe your image. Here are some good reverse image search engines: Google—especially for images taken from Google maps Yandex TinEye Flags Self-explanatory—images where you see a flag were probably taken in the place that uses said flag!...

Basic Tools strings binwalk Debuggers and Decompilers GNU Debugger Cutter