Volga CTF Quals: Crypto write-ups

Write-ups of various crypto challenges from Volga CTF Qualifier 2019


Hack.lu 2018 CTF- Relations Writeup

Relations Solved by: D1X1T, 4lph4, v3ctor, nsg99, s0rc3r3r  This was a fairly easy challenge although we are not given any encryption script. We are given three operations on the nc service to choose, XOR, ADD and DEC (decrypt). Then, we have to give an input string on which the selected operation is done. How the... Continue Reading →

InCTF 2017- GiantXOR Writeup

Author: s0rc3r3r Points: 250 Standard Encryption but can you break it? Intended Solution This challenge is a little bit tricky as compared to other crypto tasks. The text is encrypted using Repeating Key XOR, but instead of encrypting the normal plaintext, the function first encodes the message in base64 and then encrypts using Repeated Key... Continue Reading →

InCTF 2017- ‘RSA 1s Fun’ Writeup

Author: s0rc3r3r Points: 150 Mathematics and Crypto make a deadly combination! Intended Solution The challenge, as the description suggests, involves applying mathematics to solve the RSA based encryption system. The encryption code: Two different public keys e1 = 9 and e2 = 123 are being used to encrypt the same message and generate ciphertexts c1... Continue Reading →

CSAW Quals 2017 BabyCrypt Writeup

Solved by s0rc3r3r Points: 350 In this challenge, we were given a ciphertext encrypted using AES in ECB mode. In ECB mode, encryption of each plaintext block does not affect the encryption of the next plaintext block. Mostly in challenges, the attack on ciphertexts encrypted using block size mode of encryption works as follows: Mode... Continue Reading →

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