File	Doc	Category	Size	Date	Package
SecureRandom.java	API Doc	Java SE 6 API	19472	Tue Jun 10 00:25:46 BST 2008	java.security

SecureRandom

• java.lang.Object
  • java.util.Random

SecureRandom random = new SecureRandom();

SecureRandom random = new SecureRandom();
byte bytes[] = new byte[20];
random.nextBytes(bytes);

byte seed[] = random.generateSeed(20);

Fields Summary
private Provider	provider The provider.
private SecureRandomSpi	secureRandomSpi The provider implementation.
private String	algorithm
private static volatile SecureRandom	seedGenerator
static final long	serialVersionUID
private byte[]	state
private MessageDigest	digest
private byte[]	randomBytes
private int	randomBytesUsed
private long	counter

Constructors Summary
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 {@link Security#getProviders() 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. /* * This call to our superclass constructor will result in a call * to our own <code>setSeed</code> method, which will return * immediately when it is passed zero. */ super(0); getDefaultPRNG(false, null);
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 {@link Security#getProviders() Security.getProviders()} method. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard RNG algorithm names. param seed the seed. super(0); getDefaultPRNG(true, seed);
protected SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider) Creates a SecureRandom object. param secureRandomSpi the SecureRandom implementation. param provider the provider. this(secureRandomSpi, provider, null);
private SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider, String algorithm) super(0); this.secureRandomSpi = secureRandomSpi; this.provider = provider; this.algorithm = algorithm;

Methods Summary
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. param numBytes the number of seed bytes to generate. return the seed bytes. return secureRandomSpi.engineGenerateSeed(numBytes);
public java.lang.String	getAlgorithm() Returns the name of the algorithm implemented by this SecureRandom object. return the name of the algorithm or unknown if the algorithm name cannot be determined. since 1.5 return (algorithm != null) ? algorithm : "unknown";
private void	getDefaultPRNG(boolean setSeed, byte[] seed) String prng = getPrngAlgorithm(); if (prng == null) { // bummer, get the SUN implementation prng = "SHA1PRNG"; this.secureRandomSpi = new sun.security.provider.SecureRandom(); this.provider = new sun.security.provider.Sun(); if (setSeed) { this.secureRandomSpi.engineSetSeed(seed); } } else { try { SecureRandom random = SecureRandom.getInstance(prng); this.secureRandomSpi = random.getSecureRandomSpi(); this.provider = random.getProvider(); if (setSeed) { this.secureRandomSpi.engineSetSeed(seed); } } catch (NoSuchAlgorithmException nsae) { // never happens, because we made sure the algorithm exists throw new RuntimeException(nsae); } } // JDK 1.1 based implementations subclass SecureRandom instead of // SecureRandomSpi. They will also go through this code path because // they must call a SecureRandom constructor as it is their superclass. // If we are dealing with such an implementation, do not set the // algorithm value as it would be inaccurate. if (getClass() == SecureRandom.class) { this.algorithm = prng; }
public static java.security.SecureRandom	getInstance(java.lang.String algorithm) 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 {@link Security#getProviders() 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. param 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. return the new SecureRandom object. exception NoSuchAlgorithmException if no Provider supports a SecureRandomSpi implementation for the specified algorithm. see Provider since 1.2 Instance instance = GetInstance.getInstance("SecureRandom", SecureRandomSpi.class, algorithm); return new SecureRandom((SecureRandomSpi)instance.impl, instance.provider, algorithm);
public static java.security.SecureRandom	getInstance(java.lang.String algorithm, java.lang.String provider) 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 {@link Security#getProviders() 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. param 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. param provider the name of the provider. return the new SecureRandom object. exception NoSuchAlgorithmException if a SecureRandomSpi implementation for the specified algorithm is not available from the specified provider. exception NoSuchProviderException if the specified provider is not registered in the security provider list. exception IllegalArgumentException if the provider name is null or empty. see Provider since 1.2 Instance instance = GetInstance.getInstance("SecureRandom", SecureRandomSpi.class, algorithm, provider); return new SecureRandom((SecureRandomSpi)instance.impl, instance.provider, algorithm);
public static java.security.SecureRandom	getInstance(java.lang.String algorithm, java.security.Provider provider) 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. param 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. param provider the provider. return the new SecureRandom object. exception NoSuchAlgorithmException if a SecureRandomSpi implementation for the specified algorithm is not available from the specified Provider object. exception IllegalArgumentException if the specified provider is null. see Provider since 1.4 Instance instance = GetInstance.getInstance("SecureRandom", SecureRandomSpi.class, algorithm, provider); return new SecureRandom((SecureRandomSpi)instance.impl, instance.provider, algorithm);
private static java.lang.String	getPrngAlgorithm() Gets a default PRNG algorithm by looking through all registered providers. Returns the first PRNG algorithm of the first provider that has registered a SecureRandom implementation, or null if none of the registered providers supplies a SecureRandom implementation. List provs = Providers.getProviderList().providers(); for (Iterator t = provs.iterator(); t.hasNext();) { Provider p = (Provider)t.next(); for (Iterator u = p.getServices().iterator(); u.hasNext();) { Service s = (Service)u.next(); if (s.getType().equals("SecureRandom")) { return s.getAlgorithm(); } } } return null;
public final java.security.Provider	getProvider() Returns the provider of this SecureRandom object. return the provider of this SecureRandom object. return provider;
java.security.SecureRandomSpi	getSecureRandomSpi() Returns the SecureRandomSpi of this SecureRandom object. return secureRandomSpi;
public 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. This call may be used to seed other random number generators. 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. param numBytes the number of seed bytes to generate. return the seed bytes. see #setSeed if (seedGenerator == null) seedGenerator = new SecureRandom(); return seedGenerator.generateSeed(numBytes);
private static byte[]	longToByteArray(long l) Helper function to convert a long into a byte array (least significant byte first). byte[] retVal = new byte[8]; for (int i = 0; i < 8; i++) { retVal[i] = (byte) l; l >>= 8; } return retVal;
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). param numBits number of pseudo-random bits to be generated, where 0 <= numBits <= 32. return an int containing the user-specified number of pseudo-random bits (right justified, with leading zeros). int numBytes = (numBits+7)/8; byte b[] = new byte[numBytes]; int next = 0; nextBytes(b); for (int i = 0; i < numBytes; i++) next = (next << 8) + (b[i] & 0xFF); return next >>> (numBytes*8 - numBits);
public synchronized 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. param bytes the array to be filled in with random bytes. secureRandomSpi.engineNextBytes(bytes);
public synchronized 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. param seed the seed. see #getSeed secureRandomSpi.engineSetSeed(seed);
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. param seed the seed. see #getSeed /* * Ignore call from super constructor (as well as any other calls * unfortunate enough to be passing 0). It's critical that we * ignore call from superclass constructor, as digest has not * yet been initialized at that point. */ if (seed != 0) { secureRandomSpi.engineSetSeed(longToByteArray(seed)); }