It does fail if there is not enough entropy. > An error occurs if the PRNG has not been seeded with enough randomness to ensure an unpredictable byte sequence.

It does fail if there is not enough entropy. > An error occurs if the PRNG has not been seeded with enough randomness to ensure an unpredictable byte sequence. https://www.openssl.org/docs/crypto/RAND_bytes.html https://www.openssl.org/docs/crypto/RAND_bytes.html But there is also this: > Pseudo-random byte sequences generated by RAND_pseudo_bytes() will be unique if they are of sufficient length, but are not necessarily unpredictable.