Another good source explanation of the difference between urand and rand is the Linux source code, which is well commented: https://github.com/torvalds/linux/b

Another good source explanation of the difference between urand and rand is the Linux source code, which is well commented: https://github.com/torvalds/linux/blob/master/drivers/char/random.c https://github.com/torvalds/linux/blob/master/drivers/char/r... The operation is explained starting on line 52. The 2 paragraphs starting on line 78 explain the relationship behind the entropy estimator and the CSPRNG (It relies on SHA-1). > As more and more random bytes are requested [from /dev/urandom] without giving time for the entropy pool to recharge, this will result in random numbers that are merely cryptographically strong