A Classical Introduction to Cryptography - Exercise Book

About the Challenges

We plan to periodically publish some challenge related to cryptography. Most of the time, it will show how to exploit some of the classical pitfalls one may find in cryptography. Needless to say, some of these are already described in the exercise book. These challenges shall be a good way to practice some of the exciting attacks presented in the book! We will also publish a sort of Hall of Fame of the first undergraduate students who will break our challenges.

Hall of Fame!

Challenge 1

Nathalie Casati and Laurent Fasnacht solved the first challenge. Well done! They were able to factor the RSA modulus within 280 hours on an Athlon 2000+, using a modified p-1 factorization algorithm (yes, some specials 1024 bit RSA modulus are "easy" to factorize... check the book!).

Challenge 1: A (weak) 1024-bit RSA modulus

The objective of this challenge is quite simple. You are given an RSA modulus n of 1024 bits, which is the product of two primes of about 512 bits each. The goal of this challenge is to factorize n, i.e., to recover the two prime numbers p and q such that n = p*q. The value of n can be downloaded here.

If you manage to solve this challenge, send your result to

so that your name appears in the Hall of Fame!

Good Luck!

Hall of Fame for Challenge 1

Nathalie Casati and Laurent Fasnacht solved the first challenge. Well done! They were able to factor the RSA modulus within 280 hours on an Athlon 2000+, using a modified p-1 factorization algorithm.