## Generalized birthday paradox — keygenme3 by Dcoder

The birthday problem [0] asks what’s the probability that among people at least two of them have the same birthday. The “paradox” is that the answer is counterintuitive — in a group of 23, the probability is close to 50%.

## Hyperelliptic curve crypto — Dcoder’s keygenme #2

Apparently ordinary elliptic curves in crackmes are getting boring, so Dcoder decided to make things interesting with hyperelliptic curves. Due to intricate nature of HE curves, performing computations on them is more expensive, than for ordinary curves, but on the other hand HE curves provide superior bitstrength security, with regard to size of the base field, they are defined over.

In this blog post, I will try to introduce HE curves, and how to use them in crypto. Using that knowledgle, it will be easy to analyze and break a signature scheme implemented in keygenme #2 by Dcoder. Note that this won’t be a rigorous mathematical dissertation, but a “tutorial” for mathematically inclined programmer :).

## Dongles and Nyberg-Rueppel signature scheme

“Dongle me” by cyclops is, as name suggest, a crackme that requires a hardware dongle, or a software emulator. These two technical problems, combined with an uncommon authentication scheme, make it an interesting target to analyse.

## Solving confidence 2011 crackme for fun and profit

Confidence is a security conference organized in Poland. During this year’s edition (and like during few previous editions) a crackme contest took place — attendees were invited to provide a solution (serial, keygen). The fastest one would win the prize (pocketbook reader).

## Solving Pimp crackme by j00ru and Gynvael Coldwind

I figured a nice tutorial would be more interesting than yet another “hello world” post, so here it goes — solution for Pimp crackme, a winning entry for Pimp my crackme contest (polish) by j00ru and Gynvael. You can download entires (all three of them) from the contest’s page. AFAIK I’m the only person who submitted a solution.

Let’s see what we are up against.

Looks nice :).