Hacker News Reader

Comment by stillinbeta | Hacker News Reader

/dev/random will block while waiting to collect entropy from the system. /dev/urandom will be satisfied with pseudorandom numbers. That's fine for many applications (e.g. a file filled with garbage) but not acceptable for things like cryptography.

View on HN

That entropy, by the way, is derived from the keyboard and mouse devices. If you want /dev/random to go faster, move your mouse and type more ..

Can it be configured to use other sources?

Does this mean that if I've got a server with no mouse/keyboard attached, /dev/random will block forever?

Logging into my slicehost server, and running cat /dev/random | hexdump -C seems to support this, more or less - only a few lines get output unless I start typing into the terminal - then it goes marginally faster.

You can buy hardware random number generators.

http://www.entropykey.co.uk/

http://www.idquantique.com/true-random-number-generator/prod...

http://www.gamesbyemail.com/dicegenerator

...among many others.

It will also use other interrupt timings in the creation of the entropy, most notably hard drives since they're rather random on when they reply back due to it having to rotate to the right place. Not sure how this works on an SSD. I also believe if you've got some kind of hardware RNG it will use that too.

Interesting. I don't see /dev/random blocking on Mac OS X (13" MacBook Pro). I wonder what the source is?

On OS X, /dev/random and /dev/urandom are the same thing (both acting like the traditional /dev/urandom).

Reply on news.ycombinator.com