public class SecureRandom extends Random
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.SecureRandomSpi,
Random,
Serialized Form| Modifier | Constructor and 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.
|
| Modifier and Type | Method and 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 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. |
nextBoolean, nextDouble, nextFloat, nextGaussian, nextInt, nextInt, nextLongpublic SecureRandom()
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 the SecureRandom section in the Java Cryptography Architecture Standard Algorithm Name Documentation 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.
public SecureRandom(byte[] seed)
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 the SecureRandom section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard RNG algorithm names.
seed - the seed.protected SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider)
secureRandomSpi - the SecureRandom implementation.provider - the provider.public static SecureRandom getInstance(String algorithm) throws NoSuchAlgorithmException
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.
algorithm - the name of the RNG algorithm.
See the SecureRandom section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard RNG algorithm names.NoSuchAlgorithmException - if no Provider supports a
SecureRandomSpi implementation for the
specified algorithm.Providerpublic static SecureRandom getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
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.
algorithm - the name of the RNG algorithm.
See the SecureRandom section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard RNG algorithm names.provider - the name of the provider.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.Providerpublic static SecureRandom getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
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.
algorithm - the name of the RNG algorithm.
See the SecureRandom section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard RNG algorithm names.provider - the provider.NoSuchAlgorithmException - if a SecureRandomSpi
implementation for the specified algorithm is not available
from the specified Provider object.IllegalArgumentException - if the specified provider is null.Providerpublic final Provider getProvider()
public String getAlgorithm()
unknown
if the algorithm name cannot be determined.public void setSeed(byte[] seed)
seed - the seed.getSeed(int)public void setSeed(long seed)
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.
setSeed in class Randomseed - the seed.getSeed(int)public void nextBytes(byte[] 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.
protected final int next(int numBits)
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).public static byte[] getSeed(int numBytes)
This method is only included for backwards compatibility.
The caller is encouraged to use one of the alternative
getInstance methods to obtain a SecureRandom object, and
then call the generateSeed method to obtain seed bytes
from that object.
numBytes - the number of seed bytes to generate.setSeed(byte[])public byte[] generateSeed(int numBytes)
numBytes - the number of seed bytes to generate.