How do I generate random bytes with `openssl`?

Another command in openssl is rand. We invoke it like this:

$ openssl rand -hex 10
aa27660aa7e186902981

Here, 10 indicates the number of random bytes to print to standard out. -hex prints those bytes in hex format - 2 characters per byte, so 20 characters.

The output comes from a PRNG. The PRNG is seeded with, amongst other randomness sources, a file at ~/.rnd. This file contains random bytes:

$ cat ~/.rnd
33k�ɱ��%�*��#Yn�� ]w$Lkn���M|cW@9%V
...

OpenSSL apparently uses this location to store previously-gathered entropy. You can delete it at any time without any ill effects.

What can computers do? What are the limits of mathematics? And just how busy can a busy beaver be? This year, I’m writing Busy Beavers, a unique interactive book on computability theory. You and I will take a practical and modern approach to answering these questions — or at least learning why some questions are unanswerable!

It’s only $19, and you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

After months of secret toil, I and Andrew Carr released Everyday Data Science, a unique interactive online course! You’ll make the perfect glass of lemonade using Thompson sampling. You’ll lose weight with differential equations. And you might just qualify for the Olympics with a bit of statistics!

It’s $29, but you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

More by Jim

Tagged . All content copyright James Fisher 2017. This post is not associated with my employer. Found an error? Edit this page.

How do I generate random bytes with openssl?

More by Jim

How do I generate random bytes with `openssl`?