SecureRandom (Java Platform SE 8 ) (original) (raw)

This class provides a cryptographically strong random number generator (RNG).

A cryptographically strong random number minimally complies with the statistical random number generator tests specified in FIPS 140-2, Security Requirements for Cryptographic Modules, section 4.9.1. Additionally, SecureRandom must produce non-deterministic output. Therefore any seed material passed to a SecureRandom object must be unpredictable, and all SecureRandom output sequences must be cryptographically strong, as described in RFC 1750: Randomness Recommendations for Security.

A caller obtains a SecureRandom instance via the no-argument constructor or one of the getInstance methods:

  SecureRandom random = new SecureRandom();

Many SecureRandom implementations are in the form of a pseudo-random number generator (PRNG), which means they use a deterministic algorithm to produce a pseudo-random sequence from a true random seed. Other implementations may produce true random numbers, and yet others may use a combination of both techniques.

Typical callers of SecureRandom invoke the following methods to retrieve random bytes:

  SecureRandom random = new SecureRandom();
  byte bytes[] = new byte[20];
  random.nextBytes(bytes);

Callers may also invoke the generateSeed method to generate a given number of seed bytes (to seed other random number generators, for example):

  byte seed[] = random.generateSeed(20);

Note: Depending on the implementation, the generateSeed andnextBytes methods may block as entropy is being gathered, for example, if they need to read from /dev/random on various Unix-like operating systems.