Note : keys are encoded in PEM format but it’s not relevant for this example. Now you have a valid public key, we just need to compute the private exponent as the modular inverse of modulo. Note : Now, in real world RSA, you don’t use Euler’s totient function but rather Carmichael’s totient function. To choose a valid public exponent you first need to compute, also called Euler’s totient function. With and being prime integers (chosen carefully) Here comes the most important part, this must be fully understood in order to understand the attacks that will be described. As it’s an asymmetric cipher, you have two keys, a public key containing the couple (, ) and a private key containing a bunch of information but mainly the couple (, ). It doesn’t require a lot of maths knowledge to understand how it works. RSA is based on simple modular arithmetics. How simple maths can keep your data private I’m not talking about RSA used with padding as it is in real world cryptography.
#OMNISPHERE CHALLENGE CODE RSA 512 HOW TO#
I will try to be beginner friendly and repeat myself in the beginning but afterwards I will assume that the reader has learnt the concepts.īefore entering into the details on how to break RSA based challenges, let’s see how textbook RSA works. The aim of this series is to understand the attacks you use and which one is most appropriate depending on the task.
I’m not going to give you scripts that will do all the work for you but rather explain how the attacks work. In this series I will try to go through every attacks (that I’m aware of) against RSA which are useful for solving CTF tasks.