java.lang.Object java.util.Random java.security.SecureRandom
This class provides a cryptographically strong random number generator (RNG). Many 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.
This class provides a cryptographically strong pseudo-random number generator (PRNG). A cryptographically strong pseudo-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 and therefore it is required that the seed material be unpredictable and that output of SecureRandom be cryptographically strong sequences as described in
RFC 1750: Randomness Recommendations for Security
.
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 and therefore it is required that the seed material be unpredictable and that output of SecureRandom be cryptographically strong sequences as described in
RFC 1750: Randomness Recommendations for Security
.
Like other algorithm-based classes in Java Security, SecureRandom provides implementation-independent algorithms, whereby a caller (application code) requests a particular PRNG algorithm and is handed back a SecureRandom object for that algorithm. It is also possible, if desired, to request a particular algorithm from a particular provider. See the getInstance methods.
Like other algorithm-based classes in Java Security, SecureRandom provides implementation-independent algorithms, whereby a caller (application code) requests a particular RNG algorithm and is handed back a SecureRandom object for that algorithm. It is also possible, if desired, to request a particular algorithm from a particular provider. See the getInstance methods.
Thus, there are two ways to request a SecureRandom object: by specifying either just an algorithm name, or both an algorithm name and a package provider.
SecureRandom random = SecureRandom.getInstance("SHA1PRNG");the system will determine if there is an implementation of the algorithm requested available in the environment, and if there is more than one, if there is a preferred one.
SecureRandom random = SecureRandom.getInstance("SHA1PRNG", "SUN");the system will determine if there is an implementation of the algorithm in the package requested, and throw an exception if there is not.
The SecureRandom implementation attempts to completely randomize the internal state of the generator itself unless the caller follows the call to a getInstance method with a call to the setSeed method:
SecureRandom random = SecureRandom.getInstance("SHA1PRNG"); random.setSeed(seed);
After the caller obtains the SecureRandom object from the getInstance call, it can call nextBytes to generate random bytes:
byte bytes[] = new byte[20]; random.nextBytes(bytes);
The caller 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);
Constructor Summary | |
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SecureRandom
() By using this constructor, the caller obtains a SecureRandom object containing the implementation from the highest-priority installed provider that has a SecureRandom implementation. |
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SecureRandom
(byte[] seed) By using this constructor, the caller obtains a SecureRandom object containing the implementation from the highest-priority installed provider that has a SecureRandom implementation. |
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protected |
SecureRandom
(
SecureRandomSpi
secureRandomSpi,
Provider
provider) Creates a SecureRandom object. |
Method Summary | |
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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. |
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static SecureRandom |
getInstance
Generates a SecureRandom object that implements |
static SecureRandom |
getInstance
Generates a SecureRandom object for the specified RNG |
static SecureRandom |
getInstance
(
String
algorithm,
String
Generates a SecureRandom object for the specified RNG algorithm, as supplied from the specified provider, if such a RNG implementation is available from the provider. |
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 |
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nextBoolean , nextDouble , nextFloat , nextGaussian , nextInt , nextInt , nextLong |
Methods inherited from class java.lang. Object |
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clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
Constructor Detail |
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public SecureRandom()
By using this constructor, the caller obtains a SecureRandom object containing the implementation from the highest-priority installed provider that has a SecureRandom implementation.
Note that this instance of SecureRandom has not been seeded. A call to the setSeed method will seed the SecureRandom object. If a call is not made to setSeed, the first call to the nextBytes method will force the SecureRandom object to seed itself.
This constructor is provided for backwards compatibility. The caller is encouraged to use one of the alternative getInstance methods to obtain a SecureRandom object.
public SecureRandom(byte[] seed)
By using this constructor, the caller obtains a SecureRandom object containing the implementation from the highest-priority installed provider that has a SecureRandom implementation. This constructor uses a user-provided seed in preference to the self-seeding algorithm referred to in the empty constructor description. It may be preferable to the empty constructor if the caller has access to high-quality random bytes from some physical device (for example, a radiation detector or a noisy diode).
This constructor is provided for backwards compatibility. The caller is encouraged to use one of the alternative getInstance methods to obtain a SecureRandom object, and then to call the setSeed method to seed it.
protected SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider)
Method Detail |
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public static SecureRandom getInstance(String algorithm) throws NoSuchAlgorithmException
Note that the returned instance of SecureRandom has not been seeded. A call to the setSeed method will seed the SecureRandom object. If a call is not made to setSeed, the first call to the nextBytes method will force the SecureRandom object to seed itself.
public static SecureRandom getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
Note that the returned instance of SecureRandom has not been seeded. A call to the setSeed method will seed the SecureRandom object. If a call is not made to setSeed, the first call to the nextBytes method will force the SecureRandom object to seed itself.
public static SecureRandom getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
Note that the returned instance of SecureRandom has not been seeded. A call to the setSeed method will seed the SecureRandom object. If a call is not made to setSeed, the first call to the nextBytes method will force the SecureRandom object to seed itself.
public final Provider getProvider()
public StringgetAlgorithm ()
public void setSeed(byte[] seed)
public void setSeed(long seed)
This method is defined for compatibility with java.util.Random.
public void nextBytes(byte[] bytes)
protected final int next(int numBits)
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.
public byte[] generateSeed(int numBytes)