Question
I am looking for an encrypted version control system . Basically I would like to
Have all files encrypted locally before sending to the server. The server should never receive any file or data unencrypted.
Every other feature should work pretty much the same way as SVN or CVS does today.
Can anyone recommend something like this? I did a lot of searches but I cant find anything.
Solution
You should encrypt the data pipe (ssl/ssh) instead, and secure the access to the server. Encrypting the data would force SVN to essentially treat everything as a binary file. It can't do any diff, so it can't store deltas. This defeats the purpose of a delta-based approach.
Your repository would get huge, very quickly. If you upload a file that's 100kb and then change 1 byte and checkin again, do that 8 more times (10 revs total), the repository would be storing 10 * 100kb, instead of 100kb + 9 little deltas (let's call it 101kb).
Update: @TheRook explains that it is possible to do deltas with encrypted repository. So it may be possible to do this. However, my initial advice stands: it's not worth the hassle, and you're better off with encrypting the ssl/ssh pipe and securing the server. i.e. "best practices".
Solution
It is possible to create a version control system of cipher text. It would be ideal to use a stream cipher such as RC4-drop1024 or AES-OFB mode. As long as the same key+iv is used for each revision. This will mean that the same PRNG stream will be generated each time and then XOR'ed with the code. If any individual byte is different, then you have a mismatch and the cipher text its self will be merged normally.
A block cipher in ECB mode could also be used, where the smallest mismatch would be 1 block in size, so it would be ideal to use small blocks. CBC mode on the other hand can produce widely different cipher text for each revision and thus is undesirable.
I recognize that this isn't very secure, OFB and ECB modes shouldn't normally be used as they are weaker than CBC mode. The sacrifice of the IV is also undesirable. Further more it isn't clear what attack is being defended against. Where as using something like SVN+HTTPS is very common and also secure. My post is merely stating that it is possible to do this efficiently.