We are using the keytool bundled with the java installation to generate keys to do an asymmetric RSA encryption. In the light of recent events somebody asked me whats happening under the hood of the java keytool. Especially regarding the randomness of the resulting numbers. (e.g. "huh why isn't there any random user input taken like mouse movements or keyboard input?"

So what are the 'randomness sources' of the java keytool to create its keys?

I did a quick research myself however the only information I found was a post from 2000:

The keytool.exe uses the SecureRandom as basis of its random numbers.

The Sun provider for SecureRandom follows the IEEE P1363 standard,

the Sun SecureRandom provider complies with NIST's FIPS PUB 140-1 section 4.11.

The Sun provider for SecureRandom mixes in other sources of entropy with the results from the thread contention process. Among other things this includes the current time, the state of the VM's memory usage, system properties, and file system activity.

The algorithm can perform poorly in the absence of a JIT and so we are considering supplying an alternative provider which will take advantage of platform specific support for an entropy gathering device such as /dev/random or the Pentium III thermal-noise RNG.

But this was back in 2K so may be someone of you could shed some light on that and provide an update to the above (different in Java7?). Depending on your answer I would be interessted if you would advise to switch to another provider like bouncycastle...

Update: I now assume that the keytool is using java.security.SecureRandom (and thus the default provider) as a base for its random numbers. I found another interessting article, which pointed me to the file which controls the configuration of the SecureRandom API JAVA_HOME/lib/security/java.security

In there it states the following:

Select the source of seed data for SecureRandom. By default an attempt is made to use the entropy gathering device specified by the securerandom.source property. If an exception occurs when accessing the URL then the traditional system/thread activity algorithm is used. On Solaris and Linux systems, if file:/dev/urandom is specified and it exists, a special SecureRandom implementation is activated by default. This "NativePRNG" reads random bytes directly from /dev/urandom. On Windows systems, the URLs file:/dev/random and file:/dev/urandom enables use of the Microsoft CryptoAPI seed functionality. securerandom.source=file:/dev/urandom

Since we are on a windows system I assume that the Microsoft CryptoAPI is used. Since Win7 is used it is the CNG (CryptoAPI Next Generation). Does anybody know what 'use of the Microsoft CryptoAPI seed functionality.' means? The most probable method seems to be: CryptGenRandom function

Update: Oracle seem to have improved some issues with Java 8.