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Classical Cryptography

  • Cryptography FAQ The sci.crypt FAQ will answer many of your crypto questions from classical ciphers and basic definitions to modern encryption.
  • DOE Sysworks A personal favourite of mine, this site includes information on Classical Ciphers and the also features some of Lanaki's classical essays in html format. If you want the full set of Lanaki's essays then you will have to get the last few in text format from elsewhere however. If you are having difficulty with the crypts on this site then read Lanaki.
  • Crypto Drop Box An excellent resource with some great programs and links.
  • Lanaki's Crypto Course The full Lanaki course in text format.
  • A Cryptographic Compendium Another great site explaining ciphers from simple ciphers to complex modern day crypts.


  • RSA Factoring Challenge High level factoring challenges for real money.

    Other Challenge Sites

  • In no particular order, here are some other challenge sites which you may be interested in. These sites are for fun only, and not to be taken too seriously by people ;P However, the rules of challenge sites stress that: 1. Don't ask for help, if you can't do the challenges then you can't do the challenges, so go do something else instead. 2. Don't spoil it for others, many people enjoy these sites and the challenges, giving people the answers to anything does no one any good in the end. OK, enjoy:
  • HackQuest Now quite an established site and one of my personal favourites. I recommend you read the special challenges first otherwise you will find yourself doing some of the other levels again in order to complete one of the special ones.
  • ACM Problemset at Valladolid This is probably the biggest challenge type set you will ever see. About 1000 programming problems and 28000 players. You write your program and submit it by email. It is compiled and run automatically and your results emailed back straight away. The whole system is most excellent and I can see many more hours being spent on these problems.
  • Slyfx Slyfx attracts a lot of people to his game sites and the latest version is very interesting with problems starting at easy and ending at very hard :)
  • Mod-X One of the older challenge sites and now with 9 levels, each level is quite involved.
  • Reverse Course Completely rewritten and looking very good this course consists of crackmes, reversemes and math/brain fun levels. I have contributed a couple of problems to it and it should prove to be very challenging.
  • The Game The Games applet reversing challenges are a great experience. Arm yourself with a good java applet decompiler.
  • Arcanum 5000 users show that this is one of the older and more popular challenges. Unfortunately nothing has been added to it for a long time now.
  • +Ma A site of 'riddles' with some difficult and interesting problems. Persevere with the Alice problem at the start which is very hard and you will be rewarded with some nice (and easier) levels later on. The latest URL should work ok in IE.
  • HackerGames.Net summarises all of the latest challenge sites complete with reviews.
  • BlackSheep This site has rapidly become one of the best challenge sites around. Look out for my contributions to their levels :) It now has over 120 levels that are all accessible as soon as you register, it's popularity probably stems from the ability to see who is online at any moment in time and be able to message other people.
  • Net-Force BasTijs excellent site, quite original with some very difficult levels. Unfortunately it was originally in dutch and the forums although containing many hints are mostly in dutch.
  • Sers Another new site, and a cyberarmy type set of levels. A bit easy at the moment, hopefully some more levels will be up soon.
  • Mindlock Some more difficult levels, although few in number they are harder although maybe a little obscure.
  • Blind-Dice Varying levels of difficulty and a nice site although it appears a little quiet, and the most annoying thing is that it you cannot easily tell which levels you have and have not done without going to your history page.
  • Rankk The new version of the old Pyramid site, themed around ancient Egypt.
  • Aspect is one of the older challenge sites although it is unfortunately very short in its current reincarnation.
  • Open Source Institute run the geek challenges, a linear programming puzzle, bonus rounds and now reverse engineering challenge.

    Site design Cronos Sept 2001.
    All scripts and programs Cronos Sept 2001.