Question

My client wants to encrypt/compress the html-code for their medical books in the iPhone bundle, to protect their IP.

Whats is a good way to prepare this file for the app bundle, and what complementary libraries (C, Obj-C) should I use to do the decryption and decompressing on the first launch of the app?

Copying the file to ~/Documents, then working on it seems like the best solution. Thoughts?

Answer 1

Here’s a few thoughts.

If the book text is all alphanumeric data, then don’t save the data as ASCII – save them in your own binary encoded format (for instance use 5 bits instead of 8 and pack into words). That gives you a bit of compression, slight obfuscation and a very cheap (in clock cycles) decompression. You would have a data format that is quick to access on the fly and will keep the casual curious hacker out of the text. Clock cycles would be my main concern and security second.

Another idea is store the decrypt key for a typical Blowfish encryption in obfuscated format in the app. Split into two or three constants that require some odd operation to restore for instance. But of course, now the overhead of Blowfish or whatever will be your concern.

Since you will not be able to implement perfect security (perfection is extremely expensive), the IP owners will have to use traditional copyright and trade secret techniques to fully protect their property. You’ve made it harder to hack, but it’s still up to the lawyers to be diligent, just a book on the shelf in the reserved section of the library (no photocopies please!).

Cheers