Ciphers, cryptography and communications

Despite such a huge title I expect to keep everything simple.

I've always been interested in ciphers and puzzles. But I've never been this clever kid with extreme math skills, so I didn't tether my life to something obscure like pure math. Still, I'm a software engineer and I really like to tinker with things.

And couple of day ago I've finished Neal Stephenson's book Cryptonomicon and it reminded me about my interest.

What is all this about.

I have plans of making a series of posts about old ciphers. Old ones are special ones in my heart. First – because most of them are relatively simple. For almost anything ranging between Atbash and Enigma you need pretty simple modular arithmetic and a little bit of imagination.

I will try to eliminate as much math and imagination as possible from this equation by making interactive implementations of ciphers.

What about modern cryptography?

At first I need to mention that the history of cryptography has a pretty fun timeline. I call "old" everything from Atbash (~500 BC) up to Enigma (1932). And "modern" is everything from DES (1977) up to now. Between Enigma and DES we have a gap of silence when all cryptography was monopolized by military institutes. You can treat DES as the start of an era when cryptography got out of the box. It is still pretty fun since DES has severe design defects and it was declared cryptographically weak almost from the first publications. Of course, what do you expect when the NSA was involved in designing a cryptographic algorithm for public use?

Modern cryptography is complex, and part of its complexity is the applied usage of it. I don’t yet have plans to cover it, but I suggest you read this book: Bruce Schneier, Applied Cryptography Protocols

Motivational quote from it:

There are two kinds of cryptography in this world: cryptography that will stop your kid sister from reading your files, and cryptography that will stop major governments from reading your files. This book is about the latter.

Is there an uncrackable cipher?

Yep, use a one-time pad. If the pad is generated with a real RNG, nobody can crack it unless they have the pad.

What is the major flaw in any ciphers?

User. Or, if you want a less salty answer – protocol. In real life most of the governments will beat keys out of you one way or another. It is called Rubber-Hose Cryptanalysis. It may be either physical violence or you may be detained in prison like Francis Rawls. As you see, it is the case even in "democratic" countries.

I don't want to read your posts

Fine, no probs. Here is a list of incredible books on this topic:

• H. Beker and F. Piper, Cipher Systems: The Protection of Communications
• D. Kahn, The Codebreakers: The Story of Secret Writing
• D. Kahn, Kahn on Codes

What is on the plate

I expect to cover transpositional and substitutional (both mono- and polyalphabetic) ciphers. How to encrypt and decrypt texts with them.

What I gonna ignore

I'm not an expert in cryptography and cryptanalysis so I will intentionally ignore flaws in these ciphers. Most simple ciphers are extremely vulnerable to frequency analysis and with modern hardware it is boring to crack and analyze them.

What's next

No ETA, but let’s start with Atbash, Caesar cipher, Trithemius cipher and Scytale (not really a cipher, but a fun device).