Take a look at arc4random() implementations for a hint. The generator has to switch to a new key after (in the OpenBSD implementation, too lazy to check other i

Take a look at arc4random() implementations for a hint. The generator has to switch to a new key after (in the OpenBSD implementation, too lazy to check other implementations now) 1600000 bytes of output. How do you switch to a new key? OpenBSD implemented a sysctl to retrieve the output of the kernel prg. This is great, as it perfectly works in a chroot()ed environment. Other operating systems don't necessarily provide the same facility. They will try accessing /dev/urandom, and if it doesn't exist, revert to something pretty bad, like read whatever is on the stack and use that as a key. Sodium provides randombytes_random(), randombytes_uniform() and randombytes_buf() that you can use as drop-in replacements for arc4random(), arc4random_uniform() and arc4random_buf(). On Unix, the file descriptor to /dev/urandom will be kept open, and accessible after a chroot() call. On Windows, the crypto services provider will be transparently used instead.