SecureRandom (Java Platform SE 6)
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java.security
Class SecureRandom
java.lang.Object
java.util.Random
java.security.SecureRandom
All Implemented Interfaces: Serializable
public class SecureRandomextends 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);
See Also:SecureRandomSpi,
Random,
Serialized Form
Constructor Summary
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
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 SecureRandom
getInstance(String algorithm,
Provider provider)
Returns a SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm.
static SecureRandom
getInstance(String algorithm,
String provider)
Returns a SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm.
Provider
getProvider()
Returns the provider of this SecureRandom object.
static byte[]
getSeed(int numBytes)
Returns the given number of seed bytes, computed using the seed
generation algorithm that this class uses to seed itself.
protected int
next(int numBits)
Generates an integer containing the user-specified number of
pseudo-random bits (right justified, with leading zeros).
void
nextBytes(byte[] bytes)
Generates a user-specified number of random bytes.
void
setSeed(byte[] seed)
Reseeds this random object.
void
setSeed(long seed)
Reseeds this random object, using the eight bytes contained
in the given long seed.
Methods inherited from class java.util.Random
nextBoolean, nextDouble, nextFloat, nextGaussian, nextInt, nextInt, nextLong
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Constructor Detail
SecureRandom
public SecureRandom()
Constructs a secure random number generator (RNG) implementing the
default random number algorithm.
This constructor traverses the list of registered security Providers,
starting with the most preferred Provider.
A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the first
Provider that supports a SecureRandom (RNG) algorithm is returned.
If none of the Providers support a RNG algorithm,
then an implementation-specific default is returned.
Note that the list of registered providers may be retrieved via
the Security.getProviders() method.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard RNG algorithm names.
The returned SecureRandom object has not been seeded. To seed the
returned object, call the setSeed method.
If setSeed is not called, the first call to
nextBytes will force the SecureRandom object to seed itself.
This self-seeding will not occur if setSeed was
previously called.
SecureRandom
public SecureRandom(byte[] seed)
Constructs a secure random number generator (RNG) implementing the
default random number algorithm.
The SecureRandom instance is seeded with the specified seed bytes.
This constructor traverses the list of registered security Providers,
starting with the most preferred Provider.
A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the first
Provider that supports a SecureRandom (RNG) algorithm is returned.
If none of the Providers support a RNG algorithm,
then an implementation-specific default is returned.
Note that the list of registered providers may be retrieved via
the Security.getProviders() method.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard RNG algorithm names.
Parameters:seed - the seed.
SecureRandom
protected SecureRandom(SecureRandomSpi secureRandomSpi,
Provider provider)
Creates a SecureRandom object.
Parameters:secureRandomSpi - the SecureRandom implementation.provider - the provider.
Method Detail
getInstance
public static SecureRandom getInstance(String algorithm)
throws NoSuchAlgorithmException
Returns a SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm.
This method traverses the list of registered security Providers,
starting with the most preferred Provider.
A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the first
Provider that supports the specified algorithm is returned.
Note that the list of registered providers may be retrieved via
the Security.getProviders() method.
The returned SecureRandom object has not been seeded. To seed the
returned object, call the setSeed method.
If setSeed is not called, the first call to
nextBytes will force the SecureRandom object to seed itself.
This self-seeding will not occur if setSeed was
previously called.
Parameters:algorithm - the name of the RNG algorithm.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard RNG algorithm names.
Returns:the new SecureRandom object.
Throws:
NoSuchAlgorithmException - if no Provider supports a
SecureRandomSpi implementation for the
specified algorithm.Since:
1.2
See Also:Provider
getInstance
public static SecureRandom getInstance(String algorithm,
String provider)
throws NoSuchAlgorithmException,
NoSuchProviderException
Returns a SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm.
A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the specified provider
is returned. The specified provider must be registered
in the security provider list.
Note that the list of registered providers may be retrieved via
the Security.getProviders() method.
The returned SecureRandom object has not been seeded. To seed the
returned object, call the setSeed method.
If setSeed is not called, the first call to
nextBytes will force the SecureRandom object to seed itself.
This self-seeding will not occur if setSeed was
previously called.
Parameters:algorithm - the name of the RNG algorithm.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard RNG algorithm names.provider - the name of the provider.
Returns:the new SecureRandom object.
Throws:
NoSuchAlgorithmException - if a SecureRandomSpi
implementation for the specified algorithm is not
available from the specified provider.
NoSuchProviderException - if the specified provider is not
registered in the security provider list.
IllegalArgumentException - if the provider name is null
or empty.Since:
1.2
See Also:Provider
getInstance
public static SecureRandom getInstance(String algorithm,
Provider provider)
throws NoSuchAlgorithmException
Returns a SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm.
A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the specified Provider
object is returned. Note that the specified Provider object
does not have to be registered in the provider list.
The returned SecureRandom object has not been seeded. To seed the
returned object, call the setSeed method.
If setSeed is not called, the first call to
nextBytes will force the SecureRandom object to seed itself.
This self-seeding will not occur if setSeed was
previously called.
Parameters:algorithm - the name of the RNG algorithm.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard RNG algorithm names.provider - the provider.
Returns:the new SecureRandom object.
Throws:
NoSuchAlgorithmException - if a SecureRandomSpi
implementation for the specified algorithm is not available
from the specified Provider object.
IllegalArgumentException - if the specified provider is null.Since:
1.4
See Also:Provider
getProvider
public final Provider getProvider()
Returns the provider of this SecureRandom object.
Returns:the provider of this SecureRandom object.
getAlgorithm
public String getAlgorithm()
Returns the name of the algorithm implemented by this SecureRandom
object.
Returns:the name of the algorithm or unknown
if the algorithm name cannot be determined.Since:
1.5
setSeed
public void setSeed(byte[] seed)
Reseeds this random object. The given seed supplements, rather than
replaces, the existing seed. Thus, repeated calls are guaranteed
never to reduce randomness.
Parameters:seed - the seed.See Also:getSeed(int)
setSeed
public void setSeed(long seed)
Reseeds this random object, using the eight bytes contained
in the given long seed. The given seed supplements,
rather than replaces, the existing seed. Thus, repeated calls
are guaranteed never to reduce randomness.
This method is defined for compatibility with
java.util.Random.
Overrides:setSeed in class Random
Parameters:seed - the seed.See Also:getSeed(int)
nextBytes
public void nextBytes(byte[] bytes)
Generates a user-specified number of random bytes.
If a call to setSeed had not occurred previously,
the first call to this method forces this SecureRandom object
to seed itself. This self-seeding will not occur if
setSeed was previously called.
Overrides:nextBytes in class Random
Parameters:bytes - the array to be filled in with random bytes.
next
protected final int next(int numBits)
Generates an integer containing the user-specified number of
pseudo-random bits (right justified, with leading zeros). This
method overrides a java.util.Random method, and serves
to provide a source of random bits to all of the methods inherited
from that class (for example, nextInt,
nextLong, and nextFloat).
Overrides:next in class Random
Parameters:numBits - number of pseudo-random bits to be generated, where
0
generateSeed
public byte[] generateSeed(int numBytes)
Returns the given number of seed bytes, computed using the seed
generation algorithm that this class uses to seed itself. This
call may be used to seed other random number generators.
Parameters:numBytes - the number of seed bytes to generate.
Returns:the seed bytes.
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Submit a bug or featureFor further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples. Copyright 2009 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.
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