Software tools to automatically decrypt a file, whose encryption algorithm (and/or encryption keys) isn't known?

If you've written your own "novel" encryption, without any "industry standard encryption techniques", and you don't know how to test it (ie: you are not an expert cryptographer), then I can already tell you the result.

If you've written your own "novel" encryption, without any "industry standard encryption techniques", and you don't know how to test it (ie: you are not an expert cryptographer), then I can already tell you the result. Your scheme is hopelessly flawed, and can be broken by even undergraduate level cryptographers. Not that your scheme will ever encrypt anything so valuable as to be worth the time to crack.

Cryptography is NOT for the inexperienced. More than any other discipline, it constantly builds on previous knowledge. There are no "revolutions" in crypto, and a new-and-novel-scheme is NEVER recommended.

Nice answer abelenky. – Anthony May 24 '10 at 16:18 Hmmm OK I suspected of course that I'd get an answer like this, but I'd still like to try for myself, if for nothing else but to learn how things work along the way. And who knows where a little lateral thinking can sometimes lead... Say you were running a class competition for the students to write their own ciphers - is there a program you could use to test them and adjudicate the winner?

– Andrew May 24 '10 at 16:45 No, of course not. If you're running a cryptography competition, you'd have judges with the necessary experience to mathematically analyze the algorithms. If you really don't want to believe the advice posted here, write your encryption program, encrypt a plain-text file, and offer a cash prize to anyone that can decrypt the file.

– wadesworld May 24 '10 at 16:52 So, Wade, you are saying 'No, there are no such programs'? Also, offering a cash prize to decrypt a single text file - isn't that a bit unlikely, wouldn't they need more to go on? - for all they know it could be a one-time pad.

– Andrew May 24 '10 at 16:59 3 I would say that there are no such programs. In fact, I would go so far as to say that deciding whether an algorithm can be reversed is equivalent to the Halting Problem. Even an half baked implementation of such a program might run for years without determining anything useful about the strength of a cipher.

– Allen May 24 '10 at 19:10.

Bruce Schneier has written well on this very subject. Please read Memo to the Amateur Cipher Designer. You would do well to get his book Applied Cryptography, read his blog where he occasionally points out flawed schemes, read cryptanalysis papers to see what an a real attack looks like.

Attacks usually rely on mathematical properties of the algorithm. And that is just Schneier. There are many other cryptologists you could learn from.

Read the bibliography of Schneier's book for links.

Thanks for the pointers – Andrew May 24 '10 at 17:02.

If you are writing a program for fun or to learn about encryption, great, explore and learn. If you are using a major language there are lots of available libraries free to use that will do encryption properly for you. I'd highly recommend leveraging one of these libraries if you are doing this as a professional endeavor.

If you are looking to learn more about encryption start with the book Applied Cryptography from Bruce Schneier its old but will give you a good base understanding and you can find newer texts from him or other reputable authors to build upon that knowledge. He has a site at schneier.com.

Thanks for the book recommendation. – Andrew May 24 '10 at 17:01.

Crypto cracking tools are invariably algorithm-specific.

Thanks. Kind of thought that would be the first answer posted (if it's true). – Andrew May 24 '10 at 17:21.

I can't agree enough with @abelenky and @MegaCraig: if you actually care about securing data, creating your own encryption scheme is a horrible idea. If you want to learn, you may want to start with the Wikipedia article on cryptanalysis. If you follow up with the articles on various types of cryptanalysis, you can often find links to tools that will perform that specific type of cryptanalysis, e.g. , this tool for doing frequency analysis.

Thanks, Hank. I am not doing this to secure my own or anyone else's important data. I've already been reading through all the wikipedia articles.

The type of tool you linked to is what I was looking for, although I would be interested in any more sophisticated ones because I don't think frequency analysis would work whatsoever. Hopefully I'll find some. – Andrew May 24 '10 at 16:52.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.