File	Doc	Category	Size	Date	Package
SecureRandom.java	API Doc	Java SE 5 API	18625	Fri Aug 26 14:57:16 BST 2005	java.security

SecureRandom

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

SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
random.setSeed(seed);

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 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() 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. /* * 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) 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. 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 } } // set algorithm if SecureRandom not subclassed (JDK 1.1 style) if (getClass() == SecureRandom.class) { this.algorithm = prng; }
public static java.security.SecureRandom	getInstance(java.lang.String algorithm) Generates a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm. If the default provider package provides an implementation of the requested algorithm, an instance of SecureRandom containing that implementation is returned. If the algorithm is not available in the default package, other packages are searched. 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. 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 the RNG algorithm is not available in the caller's environment. 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) 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. 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. 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 the requested RNG implementation is not available from the provider. exception NoSuchProviderException if the provider has not been configured. 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) 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. Note: the provider doesn't have to be registered. 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. 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 the requested RNG implementation is not available from the provider. exception IllegalArgumentException if the 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. This method is used as the basis of all random entities returned by this class (except seed bytes). 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)); }