### Archive

Posts Tagged ‘crackme’

## Generalized birthday paradox — keygenme3 by Dcoder

The birthday problem [0] asks what’s the probability that among $n$ 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%.

Categories: Reverse Engineering

## 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 :).

Categories: Reverse Engineering

## 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.

Categories: Reverse Engineering

## 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).