SecureRandom.SecureRandom

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Syntax 1

public SecureRandom()

Description

This empty constructor automatically seeds the generator. We attempt to provide sufficient seed bytes to completely randomize the internal state of the generator (20 bytes). Note, however, that our seed generation algorithm has not been thoroughly studied or widely deployed. It relies on counting the number of times that the calling thread can yield while waiting for another thread to sleep for a specified interval.

The first time this constructor is called in a given Virtual Machine, it may take several seconds of CPU time to seed the generator, depending on the underlying hardware. Successive calls run quickly because they rely on the same (internal) pseudo-random number generator for their seed bits.

The seeding procedure implemented by this constructor ensures that the sequence of pseudo-random bytes produced by each SecureRandom instance yields no useful information about the byte-sequence produced by any other instance. If however, the user wishes to produce multiple instances with truly unrelated seeds, the following code yields the desired result (at substantial CPU cost per instance!):

 SecureRandom rnd = new SecureRandom(SecureRandom.getSeed(20));

Syntax 2

public SecureRandom( byte seed[] )

Parameters

seed: the seed.

Description

This constructor uses a user-provided seed in preference to the self-seeding algorithm referred to in the empty constructor description. It may be preferable to the empty constructor if the caller has access to high-quality random bytes from some physical device (for example, a radiation detector or a noisy diode).