On macOS, /dev/random never blocks. From the beginning up until 2014 or so, this was blatantly insecure: the only initial entropy was the system clock! In mic

On macOS, /dev/random never blocks. From the beginning up until 2014 or so, this was blatantly insecure: the only initial entropy was the system clock! In microseconds, not seconds, thankfully, but that's still a very low amount of entropy. securityd in userland would send the kernel more entropy once it came up, but before that point, /dev/random would just spew low-quality random numbers. Since 2014, however, macOS has expected to get a random seed from the bootloader, which in turn gets it from rdrand if available, or some complicated timer stuff if not. I'm not sure how secure the latter is, but as of Mojave, there are no longer any supported Macs without rdrand, making the issue moot...