Recently we ran into a problem where one of our Linux-based virtual machines was really slow due to a chronic shortage of "entropy".
I'm wondering if Windows virtual machines would suffer from the same problem. (A Google search gave me no relevant hits, but I could be using the wrong search terms.)
I have several Entropy Keys with egd in front of them and then all load balanced by haproxy. I then have many client machines using the haproxy service IP as a network source of entropy. I have no idea how much entropy they are requesting.
The Entropy Keys can produce a limited amount of usable entropy. The specs say about 30 kilobit/sec minimum. As far as I can see, the Entropy Key doesn't have a way to query how much it is being asked for. The EGD protocol seems quite hard to sniff to find this information. Clients can request a variable amount of entropy, and they might not get back the same amount.
Has anyone found a simple way to measure how much is being requested from an Entropy Key?
It would be good to know, in order to be able to plan when additional keys are required, and to spot haywire clients.
In my Apache configuration I have these lines:
SSLRandomSeed connect builtin
SSLRandomSeed connect file:/dev/random
SSLRandomSeed connect file:/dev/urandom 1024
How, exactly, does Apache interpret this? Does it first try builtin and then move to /dev/random if that fails? If it uses /dev/random, and /dev/random then runs out of entropy, does it automatically switch to /dev/urandom? Is there an Apache document somewhere that explains all this?
As you might know that it's not as easy to generate entropy on a virtual machine as on a "normal" pc. Generating a gpg-key on a virtual machine can take a while, even with the correct tools.
There are plenty more crypto functions out there which aren't so entropy aware as gpg is.
So can one say that cryptography is less secure on a virtual machine?
If I run this command in Ubuntu
sudo cat /proc/sys/kernel/random/entropy_avail
it returns a number that indicates how much "entropy" is available to the kernel, but that's about all I know. What unit is this entropy measured in? What is it used for? I've been told it's "bad" if that number is "low". How low is "low" and what "bad" things will happen if it is? What's a good range for it to be at? How is it determined?