Insecure random number generation in getkey()

[rcbarnett-zz]

MODSEC-316: I think there are a couple of problems with the getkey() implementation.

1. If the purpose of the key is to use it for crypto operations (I have not reviewed any other code, so I don't know.), then the standard random number generator is not sufficient. You'll want to use a proper PRNG.
2. Even that aside, in the current implementation, time is used to seed the RNG, but its resolution of the clock is in seconds. Which means it is easily predictable.
3. Re-seeding in the loop does not contribute to the randomness, and may actually be affecting it negatively.
4. From a glance, the loop does not seem correct. There might be an off-by-one issue there.

[rcbarnett-zz]

Original reporter: ivanr

[rcbarnett-zz]

bpinto: The loop issue is already fixed. Don't know what -1 was there :)

I was thinking about to use some proper PRNG but all ideas are platform dependent. Do you have a good idea how to implement something real random that is independent of platform ?

[rcbarnett-zz]

bpinto: I was using linear congruential approach but it would require 64 bits words for better efficiency. I will that if i found something better i will implement

thanks

[rcbarnett-zz]

ivanr: Is this random key stored somewhere, or is it truly ephemeral? If the latter, then it would probably break many requests on every re-configuration. As such, it's probably not very useful and you could just remove this functionality.

[rcbarnett-zz]

bpinto: Yes. If the user reload apache then modsec could drop some old session. But i prefer keep it on the game and add the ability to persist the key in the future.