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. * *
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 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); ** * @see java.security.SecureRandomSpi * @see java.util.Random * * @version 1.47, 12/19/03 * @author Benjamin Renaud * @author Josh Bloch */ public class SecureRandom extends java.util.Random { /** * The provider. * * @serial * @since 1.2 */ private Provider provider = null; /** * The provider implementation. * * @serial * @since 1.2 */ private SecureRandomSpi secureRandomSpi = null; /* * The algorithm name of null if unknown. * * @serial * @since 1.5 */ private String algorithm; // Seed Generator private static SecureRandom seedGenerator = null; /** *
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() {
/*
* This call to our superclass constructor will result in a call
* to our own setSeed method, which will return
* immediately when it is passed zero.
*/
super(0);
getDefaultPRNG(false, null);
}
/**
*
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.
*/
public SecureRandom(byte seed[]) {
super(0);
getDefaultPRNG(true, seed);
}
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;
}
}
/**
* Creates a SecureRandom object.
*
* @param secureRandomSpi the SecureRandom implementation.
* @param provider the provider.
*/
protected SecureRandom(SecureRandomSpi secureRandomSpi,
Provider provider) {
this(secureRandomSpi, provider, null);
}
private SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider,
String algorithm) {
super(0);
this.secureRandomSpi = secureRandomSpi;
this.provider = provider;
this.algorithm = 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
*/
public static SecureRandom getInstance(String algorithm)
throws NoSuchAlgorithmException {
Instance instance = GetInstance.getInstance("SecureRandom",
SecureRandomSpi.class, algorithm);
return new SecureRandom((SecureRandomSpi)instance.impl,
instance.provider, algorithm);
}
/**
* 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
*/
public static SecureRandom getInstance(String algorithm, String provider)
throws NoSuchAlgorithmException, NoSuchProviderException {
Instance instance = GetInstance.getInstance("SecureRandom",
SecureRandomSpi.class, algorithm, provider);
return new SecureRandom((SecureRandomSpi)instance.impl,
instance.provider, algorithm);
}
/**
* 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
*/
public static SecureRandom getInstance(String algorithm,
Provider provider) throws NoSuchAlgorithmException {
Instance instance = GetInstance.getInstance("SecureRandom",
SecureRandomSpi.class, algorithm, provider);
return new SecureRandom((SecureRandomSpi)instance.impl,
instance.provider, algorithm);
}
/**
* Returns the SecureRandomSpi of this SecureRandom object.
*/
SecureRandomSpi getSecureRandomSpi() {
return secureRandomSpi;
}
/**
* Returns the provider of this SecureRandom object.
*
* @return the provider of this SecureRandom object.
*/
public final Provider getProvider() {
return provider;
}
/**
* 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
*/
public String getAlgorithm() {
return (algorithm != null) ? algorithm : "unknown";
}
/**
* 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
*/
synchronized public void setSeed(byte[] seed) {
secureRandomSpi.engineSetSeed(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
*/
public void setSeed(long seed) {
/*
* 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));
}
}
/**
* 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.
*/
synchronized public void nextBytes(byte[] bytes) {
secureRandomSpi.engineNextBytes(bytes);
}
/**
* 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).
*/
final protected int next(int numBits) {
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);
}
/**
* 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
*/
public static byte[] getSeed(int numBytes) {
if (seedGenerator == null)
seedGenerator = new SecureRandom();
return seedGenerator.generateSeed(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.
*/
public byte[] generateSeed(int numBytes) {
return secureRandomSpi.engineGenerateSeed(numBytes);
}
/**
* Helper function to convert a long into a byte array (least significant
* byte first).
*/
private static byte[] longToByteArray(long l) {
byte[] retVal = new byte[8];
for (int i = 0; i < 8; i++) {
retVal[i] = (byte) l;
l >>= 8;
}
return retVal;
}
/**
* 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.
*/
private static String getPrngAlgorithm() {
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;
}
// Declare serialVersionUID to be compatible with JDK1.1
static final long serialVersionUID = 4940670005562187L;
// Retain unused values serialized from JDK1.1
/**
* @serial
*/
private byte[] state;
/**
* @serial
*/
private MessageDigest digest = null;
/**
* @serial
*
* We know that the MessageDigest class does not implement
* java.io.Serializable. However, since this field is no longer
* used, it will always be NULL and won't affect the serialization
* of the SecureRandom class itself.
*/
private byte[] randomBytes;
/**
* @serial
*/
private int randomBytesUsed;
/**
* @serial
*/
private long counter;
}