> On Jan 6, 2016, at 12:01 AM, Sean Mullan <sean.mul...@oracle.com> wrote:
>
> If you think getFullEntropy is sufficient, then let's just keep the one
> method.
I thought about this more and we can actually do
/**
* An interface of a source of entropy input.
* <p>
* This interface has 2 methods returning byte arrays containing entropy.
* The result of {@link #getFullEntropy} contains full entropy and that of
* {@link #getEntropy} contains the request amount of entropy but might not
* be full. The default implementation of the methods inside this interface
* are dependent on each other. An implementation must implement at least
* one of them to be useful.
*
* @since 1.9
*/
public interface EntropyInput {
/**
* Fills a byte array with full entropy.
* <p>
* This method might block and/or fail.
*
* @implSpec The default implementation calls {@link #getEntropy}
* to return a byte array which might not have full entropy, and then
* calls the hashdf conditioning function defined in NIST SP 800-90Ar1
* 10.3.1 to condense it into an array with full entropy.
*
* @param entropy the byte array with filled entropy.
* @throws EntropyNotAvailableException if not enough entropy is available.
*/
default void getFullEntropy(byte[] entropy) {
byte[] raw = getEntropy(entropy.length);
if (raw.length != entropy.length) {
try {
MessageDigest md = MessageDigest.getInstance("SHA-256", "SUN");
raw = HashDrbg.hashDf(md, md.getDigestLength(),
entropy.length, raw);
} catch (Exception e) {
throw new InternalError(e);
}
}
System.arraycopy(raw, 0, entropy, 0, raw.length);
}
/**
* Returns a byte array with at least length*8 bits of entropy.
* <p>
* This method might block and/or fail.
*
* @implSpec The default implementation calls {@link #getFullEntropy}
* to return a byte array which has full entropy.
*
* @param length the minimum size of entropy requested in bytes
* @return a byte array containing entropy
* @throws EntropyNotAvailableException if not enough entropy is available.
*/
default byte[] getEntropy(int length) {
byte[] result = new byte[length];
getFullEntropy(result);
return result;
}
}
