A challenger’s guide to basic crypto

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A challenger’s guide to basic crypto

Postby sabretooth » Fri Jun 27, 2008 7:23 pm

A challenger’s guide to basic crypto

Written by sabretooth

Greetings to all.
When talking about crypto we can mean a great deal things, but when confining this term to typical ‘challenge site’ scenarios then the following will be helpful.

I’m sure many of you have heard of SNEAK which was created by snarkles of the cyberarmy. Vermillion is a tool based on this and has many more functions. Try it out at http://vermillion.t35.com/ it even links to rainbow tables for cracking those pesky md5/sha hashes and also provides links to pages used to break playfair, vigenere etc

At this point for those of you saying ‘wtf’ then I suggest you get googling or head to wikipedia. I’m not going to do your homework for you but I’ll suggest some starting points.

Look for things like column transposition, playfair, vigenere, atbash, Caesar/ceasar cipher, rot-13, base 64, hex, md5.

It is useful to be able to recognise ciphers and encryptions by sight. Some of them are fairly obvious, for example a code ending in == is usually base64.
A long paragraph of gvt I lsye bsgt afdre ok dhy…. Could very well be basic mono-alpha substitution. Usually things which mention p*q are a basic starting point for RSA. WorDs WhicH ArE SPElt Like ThIS could very well be bacon cipher, or even binary if you take the caps as 1 and lowercase as 0… or even morse code.

A lot of this is common sense, but much more than that it is logically analysing what you have and applying techniques which logically fit.
For example there is very little point in applying atbash to a string of numbers. (go figure)

A final point I wish to make is about cracking one-way encryptions like MD5 and SHA1. One-way means it can be encrypted by a tool but cannot be reversed as easily. A couple of great programs for this though are ‘Cain and Abel’ and ‘cryptool’ (the latter can also have a go at RSA and playfair etc.)

This was by no means intended to get you through lots of crypto challenges, but use the ciphers and encryptions mentioned in this post as points of research and you’ll be well on the way to doing it for yourself !

Good luck and peace out

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Postby Nuke » Mon Jun 30, 2008 7:46 am

Good post, thx for the hint Sabre! :D
Look at you, hacker. A pathetic creature of meat and bone, panting and sweating as you run through my corridors. How can you challenge a perfect, immortal machine?
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