java.security

Class SecureRandom

public class SecureRandom extends Random

An interface to a cryptographically secure pseudo-random number generator (PRNG). Random (or at least unguessable) numbers are used in all areas of security and cryptography, from the generation of keys and initialization vectors to the generation of random padding bytes.

Constructor Summary
	SecureRandom() Default constructor for SecureRandom.
	SecureRandom(byte[] seed) A constructor for SecureRandom.
protected	SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider) A constructor for SecureRandom.

Method Summary
byte[]	generateSeed(int numBytes) Returns the specified number of seed bytes.
String	getAlgorithm() Returns the algorithm name used or "unknown" when the algorithm used couldn't be determined (as when constructed by the protected 2 argument constructor).
static SecureRandom	getInstance(String algorithm) Returns an instance of a `SecureRandom` from the first provider that implements it.
static SecureRandom	getInstance(String algorithm, String provider) Returns an instance of a `SecureRandom` for the specified algorithm from the named provider.
static SecureRandom	getInstance(String algorithm, Provider provider) Returns an instance of a `SecureRandom` for the specified algorithm from the given provider.
Provider	getProvider() Returns the provider being used by the current SecureRandom class.
static byte[]	getSeed(int numBytes) Returns the given number of seed bytes.
protected int	next(int numBits) Generates an integer containing the user specified number of random bits.
void	nextBytes(byte[] bytes) Generates a user specified number of bytes.
void	setSeed(byte[] seed) Seeds the SecureRandom.
void	setSeed(long seed) Seeds the SecureRandom.

Constructor Detail

SecureRandom

public SecureRandom()

Default constructor for SecureRandom. It constructs a new SecureRandom by instantating the first SecureRandom algorithm in the default security provier. It is not seeded and should be seeded using setSeed or else on the first call to getnextBytes it will force a seed. It is maintained for backwards compatibility and programs should use {@link #getInstance(java.lang.String)}.

SecureRandom

public SecureRandom(byte[] seed)

A constructor for SecureRandom. It constructs a new SecureRandom by instantating the first SecureRandom algorithm in the default security provier. It is seeded with the passed function and is useful if the user has access to hardware random device (like a radiation detector). It is maintained for backwards compatibility and programs should use getInstance.

Parameters: seed Seed bytes for class

SecureRandom

protected SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider)

A constructor for SecureRandom. It constructs a new SecureRandom using the specified SecureRandomSpi from the specified security provier.

Parameters: secureRandomSpi A SecureRandomSpi class provider A Provider class

Method Detail

generateSeed

public byte[] generateSeed(int numBytes)

Returns the specified number of seed bytes.

Parameters: numBytes number of seed bytes to get

Returns: an array containing the seed bytes

getAlgorithm

public String getAlgorithm()

Returns the algorithm name used or "unknown" when the algorithm used couldn't be determined (as when constructed by the protected 2 argument constructor).

Since: 1.5

getInstance

public static SecureRandom getInstance(String algorithm)

Returns an instance of a SecureRandom from the first provider that implements it.

Parameters: algorithm The algorithm name.

Returns: A new SecureRandom implementing the given algorithm.

Throws: NoSuchAlgorithmException If no installed provider implements the given algorithm. IllegalArgumentException if algorithm is null or is an empty string.

getInstance

public static SecureRandom getInstance(String algorithm, String provider)

Returns an instance of a SecureRandom for the specified algorithm from the named provider.

Parameters: algorithm The algorithm name. provider The provider name.

Returns: A new SecureRandom implementing the chosen algorithm.

Throws: NoSuchAlgorithmException If the named provider does not implement the algorithm, or if the implementation cannot be instantiated. NoSuchProviderException If no provider named provider is currently installed. IllegalArgumentException if either algorithm or provider is null or empty.

getInstance

public static SecureRandom getInstance(String algorithm, Provider provider)

Returns an instance of a SecureRandom for the specified algorithm from the given provider.

Parameters: algorithm The SecureRandom algorithm to create. provider The provider to use.

Throws: NoSuchAlgorithmException If the algorithm cannot be found, or if the class cannot be instantiated. IllegalArgumentException if either algorithm or provider is null, or if algorithm is an empty string.

getProvider

public final Provider getProvider()

Returns the provider being used by the current SecureRandom class.

Returns: The provider from which this SecureRandom was attained

getSeed

public static byte[] getSeed(int numBytes)

Returns the given number of seed bytes. This method is maintained only for backwards capability.

Parameters: numBytes number of seed bytes to get

Returns: an array containing the seed bytes

protected final int next(int numBits)

Generates an integer containing the user specified number of random bits. It is right justified and padded with zeros.

Parameters: numBits number of random bits to get, 0 <= numBits <= 32;

Returns: the random bits

nextBytes

public void nextBytes(byte[] bytes)

Generates a user specified number of bytes. This function is the basis for all the random functions.

Parameters: bytes array to store generated bytes in

setSeed

public void setSeed(byte[] seed)

Seeds the SecureRandom. The class is re-seeded for each call and each seed builds on the previous seed so as not to weaken security.

Parameters: seed seed bytes to seed with

setSeed

public void setSeed(long seed)

Seeds the SecureRandom. The class is re-seeded for each call and each seed builds on the previous seed so as not to weaken security.

Parameters: seed 8 seed bytes to seed with