How to securely store a PrivateKey in code [duplicate]

Answer 1

It's impossible to secure a key in an untrusted environment. You can obfuscate your code, you can create a key from arbitrary variables, whatever. Ultimately, assuming that you use the standard javax.crypto library, you have to call Mac.getInstance(), and sometime later you'll call init() on that instance. Someone who wants your key will get it.

However, I think the solution is that you tie the key to the environment, not the program. A signature is meant to say that the data originated from a known source, and has not been tampered with since that source provided it. Currently, you're trying to say "guarantee that my program produced the data." Instead, change your requirement to "guarantee that a particular user of my program produced the data." The onus is then shifted to that user to take care of his/her key.

Answer 2

Forget about obscuring it in the code. It will only make your software harder to read, debug and maintain. You'll also be nailed if your software has to go through a security audit.

If you can't put the key in secure storage (securely on disk, secure memory or a passphrase in someones head), don't bother with anything else.

If you're in a *nix environment, storing the key on disk with root/root 400 permissions might be "good enough".

On Windows, you could use the DPAPI to store the data in Microsofts secure memory.

You could also use a lightweight PBE to encrypt the sensitive key and have the user enter the passphrase when the application starts up.

Answer 3

First off - good on you for thinking about this problem!

Is it possible to instead generate a private key, communicate with your Certificate Authority and have it sign the key (and manage a CRL as well)?

As an alternative, if this is going to be running on Windows, you can use the Crypto API to securely store a private key that is marked as not-exportable. How you distribute that key securely can be another challenge though.

Answer 4

Whose private key is that? The private key is supposed to be private, so it is wrong to distribute it.

Answer 5

Can you break the private key out into two parts: store one in your program, then interactively request the second half - when your app starts ?