(Why) Cryptography & Steganography

I have the following two questions, for which, in my opinion, many of you would like to find the answer:

1) Why would you learn cryptography except for doing challenges? How much could it help you in "real" situations. And when I mean cryptography, I'm especially thinking about vigenere, playfair and so on, not at md5, des, etc.

2) Why would you learn steganography, except for doing challenges?

Because you never know what knowledge you are going to need, what parts of of these fields might apply to something you encounter. Frequency analysis is not limited to languages. Perhaps you learn about certain mathematical concepts because of interesting ciphers you encounter. Maybe learning about these things in this context is easier for you or gives you new insights.

I suspect you are thinking to much like "when am I ever going to encounter playfair in real life?" You are not, in all likeliness. But learning playfair need not just learn you playfair.

Quote from Hertz

Oct 19, 2011 - 15:01:05

1) Why would you learn cryptography except for doing challenges? How much could it help you in "real" situations. And when I mean cryptography, I'm especially thinking about vigenere, playfair and so on, not at md5, des, etc.

1) Fun-- same reason as all the challenge site problems.
2) History
3) Cognitive workout. Its good for observation and logic, for starters. They also make very good practice algorithms when you are learning a language.

If you only need to hide information for half an hour some of these are still viable options and I'd guess 99% of the world wouldn't be able to read your messages. If you are hiding messages from the police, playfair won't work, but for most of the world it would, especially given that most of the world is just lazy and would opt for TV over cracking your message. I'd still go with GPG though, if it were me, so really its back to 'fun'.

Quote from Hertz

Oct 19, 2011 - 15:01:05

2) Why would you learn steganography, except for doing challenges?

Steg is a different story. If I needed to communicate covertly with agents around the world, I'd do it with text or image steg in blog comments or online forums on various and sundry sites, and I've seen speculation that some organizations are doing just that. Such messages would be hard to find, hard to trace, and hard to decode/decrypt. Steg is a very powerful mechanism for transmitting secrets since there are a lot of different ways to do it, making automatic discovery/decoding difficult. Of the various steg challenges I've worked on, maybe a couple were cracked automatically by a software tool. Most I've had to reverse and decode by hand. Combined with encryption you've got a nasty beast of a message vehicle, and one that doesn't even look like a vehicle at all.