SHA1PRNG forced in SecureRandom

[nicolasbon38]

In the KeyHelper class, an instance of SecureRandom is created and "SHA1PRNG" is passed to the constructor.

Why did you do this choice ? Wouldn't calling the constructor without argument to let the best PRNG on a given platform to be picked ?

[jrose-signal]

Excitingly, that code is over ten years old! Well before my time at Signal, and before I did anything with Android.

Given that we use the default SecureRandom elsewhere in libsignal, it would make sense to do the same here. There isn't even a performance argument, since registration IDs are only generated at registration and when you change your number.

[jrose-signal]

Ha, I accidentally autoclosed this with the fix in the private pre-release repo. The hardcoding of SHA1PRNG will be removed in the next release of libsignal, thanks for calling it out!