Difference in output streams.

Bryan Duffy bryan88 at yahoo.com
Sun Nov 13 00:07:48 GMT 2011

Have the Entropy Key installed and working on Ubuntu 11.10 with no apparent problems.  Question about the
output from the various data streams available on the device sockets.

In Linux without an entropy key /dev/random is "blocked" and released in chunks from the entropy pool as entropy is available and /dev/urandom is not blocked and is a basically a PRNG that is rekeyed (not sure how often) from the entropy pool.

With the Entropy Key I notice there are 4 data streams:
1. The new /dev/tty???? has encrypted/armoured data from the key to the entropyd,
2. /dev/random seems to function the same as before, but much faster due to the Entropy Key,
3. /dev/urandom seems to function from a PRNG as before, but I would assume it is getting rekeyed much more frequently, so the data should be of a better quality (is that a fair assumption?).
4.  /dev/hwrng which is producing data at about 4 times as fast as /dev/random.

What are the entropy qualities of these devices with Entropy Key installed?
Which ones are truly random and which are rapidly keyed PRNGs?
Is /dev/hwrng direct output from the entropy key (after decrypting) or does it get modified by the kernel in some other way (mixed/rehashed)?
Lastly, why (maybe it's just my machine) does the /dev/hwrng output data about 4 times as fast as /dev/random if they are both being supplied by the same source of purely random data?  Shouldn't they be similar is rate.

I was hoping that someone could comment on these questions, and whether or not  /dev/hwrng is suitable for cryptographic keys or should I stick with /dev/random?

Thank you!

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