Question

My application needs to use a couple of hard-coded symmetric cryptographic keys (while I know that storing a public key would be the only perfect solution, this is non-negotiable). We want the keys to be stored obfuscated, so that they won’t be recognizable by analyzing the executable, and be “live” in memory for as little time as possible – as to increase the difficulty of a memory dump retrieving them in clear-text. I’m interested in using C++ features (using some sort of scoped_key comes to mind). The solution must be portable – Windows, Linux, MacOS -, so it cannot take advantage of the operating system crypto API.

How would you go about designing such a system? Thanks a lot.

Answer 1

your scoped_key can be simply a KeyHolder object on the stack. Its constructor takes the obfuscated buffer and makes a real key out of it and its destructor zeros out the memory and deallocates the memory.

As for how to actually obfuscate the key in the binary, One silly choice you might try is put inside a much larger random binary block and remember its offset and size and probably XOR it with some short random sequence.

If you do the XORing thing you can actually avoid ever having the real key in memory. simply modify the decryption to read a byte from the key and before using it, to XOR it with the appropriate value.

*Add here disclaimer on how foolish security through obscurity is*