compact1, compact2, compact3

java.security

Class SecureRandom

java.lang.Object

java.util.Random

java.security.SecureRandom

All Implemented Interfaces:

Serializable

public class SecureRandom
extends Random

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 and nextBytes methods may block as entropy is being gathered, for example, if they need to read from /dev/random on various Unix-like operating systems.

See Also:

SecureRandomSpi, Random, Serialized Form

Constructor Summary

Constructors

Modifier	Constructor	Description
	SecureRandom()	Constructs a secure random number generator (RNG) implementing the default random number algorithm.
	SecureRandom(byte[] seed)	Constructs a secure random number generator (RNG) implementing the default random number algorithm.
protected	SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider)	Creates a SecureRandom object.

Method Summary

Modifier and Type	Method	Description
byte[]	generateSeed(int numBytes)	Returns the given number of seed bytes, computed using the seed generation algorithm that this class uses to seed itself.
String	getAlgorithm()	Returns the name of the algorithm implemented by this SecureRandom object.
static SecureRandom	getInstance(String algorithm)	Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm.
static