Points: 200 Description: Rivest comes up with an encryption, and Shamir creates a service for decrypting any cipher text encrypted using Rivests’s encryption. Adleman is asked to decrypt a specific ciphertext, but he is not able to do so directly through Shamir’s service. Help him out. This CTF had some okay-ish crypto challenges(didn't like the first... Continue Reading →

# CNVService- AceBear CTF 2018 Writeup

This challenge was by far the most interesting and tricky Bit Flipping Attack I had come across, and I couldn't resist but share the write-up of this challenge. The challenge is one of the best illustrations of Bit Flipping Attack on Chained Block Cipher modes so, it is highly recommended for people who want to get... Continue Reading →

# Rule86 – Insomni’hack Teaser 2018 Writeup

Points: 78 Description: Kevin is working on a new synchronous stream cipher, but he has been re-using his key. Although I could not solve the challenge completely during the CTF (I was stuck in the last stage), I liked the idea behind the last part of the exploit and so I am writing this post... Continue Reading →

# DLP and Baby Step Giant Step Algorithm

Topics covered: Cyclic Groups Discrete Logarithm Problem Applications Attacks on DLP Brute Force Attack on DLP Baby Step Giant Step Algorithm CTF Challenges based on DLP Prerequisites: Mathematical Structures Cyclic Groups Abelian Groups in which all the elements can be produced using a single element in the group. This element is known as a generator... Continue Reading →

# Finite Fields- Number Theory

This blog post covers one of the most important Mathematical Structures for Cryptography- Fields. It is used in both Symmetric and Asymmetric key Cryptography. This blog post gives a basic introduction to Finite Fields and arithmetic operations on it, but I hope the purpose of it is served- to make people, who don't have basic knowledge... Continue Reading →

# ASIS Finals CTF 2017- Gracias Writeup

Points: 287 Solves: 9 Category: Crypto Description: Some people think that combination of cryptographic systems will definitely improve the security. That's your turn to prove them wrong. This challenge is a bit simpler than it looks like. It is a multi-prime RSA challenge where we are given an encryption script, which has two functions, one... Continue Reading →

# Polynomial Interpolation

I have been reading "How to Share a Secret" in detail for the past few weeks, a revolutionary research paper by Adi Shamir. This paper applies some of the concepts of Number Theory and Algebra, one of which is polynomial interpolation, and has been used to construct a secure and reliable key management system. The... Continue Reading →

# CBC Bit-Flipping Attack

In this blog post, the attack on CBC mode of block cipher encryption will be discussed and in the end, detailed writeup for the 16th challenge of Matasano-Crypto-Challenge i.e. about the Bit Flipping Attack in AES-CBC will be provided with explanation! I want the reader to go through these concepts discussed in the following blog... Continue Reading →

# Block-size Detection

In the previous blog, "Detecting the mode of block cipher being used" was discussed. In this blog, the second step in the attacking of a block cipher i.e. detecting the block size of the cipher, will be discussed. Link to the implementation script has been given at the end of this post which is written... Continue Reading →