How to encrypt a text file using C?

Question

I want to have a program like this:

scanf("%s", name);
scanf("%s", id);
scanf("%d", &age);

Now I want to write name, id and age to a file, but the file should be encrypted, so that only my program can read back the data it wrote.

Do I need to use one of the encryption libraries mentioned here (they all are pretty heavy duty libraries, I just need to encrypt a text file), or is there any other simpler method?

If an encryption library is the solution, which one is best suited for a simple text file encryption?

Answer 1

If you want security, it is a mistake to roll your own encryption library. Use a well established encryption library (even if it may seem bloated), and leave security and its proper implementation to the experts.

If you can use C++, I suggest Crypto++, and if you can't use C++, then I suggest you implement a C wrapper library around Crypto++. Another possibility is libcrypto, although it lacks support for AES.

I should warn you, though, that if the program and the text file are on the same machine, you will need to have the password supplied externally (e.g. by the user); passwords that are embedded in programs are easily extracted, and offer no security at all. If the program is inaccessible (e.g. it is located on a webserver, and someone with the text file won't have access to the executable), then it is ok.

Answer 2

Better use a symmetric-key algorithm, as AES. You can find small sourcecodes here for instance.

If your applications are critical, then you should use the libraries you linked to.