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Is there a tool available for Linux systems that can measure the "quality" of entropy on the system?

I know how to count the entropy:

cat /proc/sys/kernel/random/entropy_avail

And I know that some systems have "good" sources of entropy (hardware entropy keys), and some don't (virtual machines).

But is there a tool that can provide a metric as to the "quality" of the entropy on the system?

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Im interested, Why would you want to calculate entropy of a system? –  whoami Feb 16 '12 at 11:45
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migrated from crypto.stackexchange.com Feb 15 '12 at 19:03

This question came from our site for software developers, mathematicians and others interested in cryptography.

3 Answers

up vote 4 down vote accepted

http://www.fourmilab.ch/random/ works for me.

sudo apt-get install ent
head -c 1M /dev/urandom > /tmp/out
ent /tmp/out
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this is good thanks @Marcin –  Nikhil Mulley Feb 16 '12 at 23:46
    
Cool tool. You can check a device in just one command with dd if=/dev/urandom bs=1M count=1 | ent –  l0b0 Jun 13 '13 at 15:22
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I think you are looking for:

cat /proc/sys/kernel/random/entropy_avail
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Sorry, no, I'm well aware of entropy_avail. I'm trying to measure the quality of that entropy. –  Dustin Kirkland Feb 15 '12 at 22:10
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Tools can only ever give you an upper bound on the entropy. For most uses, in particular security related uses you're more interested in a lower bound.

Calculating the entropy of an arbitrary file is mathematically impossible, so there can be no tool that can do it.

I can easily write a file generator that generates very low entropy files, but will still pass your entropy tests. Just use a crypto PRNG with a small seed.

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