/*
* @(#)SecureRandom.java 1.47 03/12/19
*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.security;
import java.util.*;
import java.security.Provider.Service;
import sun.security.jca.*;
import sun.security.jca.GetInstance.Instance;
/**
* <p>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.
*
* <p>A cryptographically strong random number
* minimally complies with the statistical random number generator tests
* specified in <a href="http://csrc.nist.gov/cryptval/140-2.htm">
* <i>FIPS 140-2, Security Requirements for Cryptographic Modules</i></a>,
* 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 <a href="http://www.ietf.org/rfc/rfc1750.txt">
* <i>RFC 1750: Randomness Recommendations for Security</i></a>.
*
* <p>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 <code>getInstance</code> methods.
*
* <p>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.
*
* <ul>
*
* <li>If just an algorithm name is specified, as in:
* <pre>
* SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
* </pre>
* 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.<p>
*
* <li>If both an algorithm name and a package provider are specified, as in:
* <pre>
* SecureRandom random = SecureRandom.getInstance("SHA1PRNG", "SUN");
* </pre>
* the system will determine if there is an implementation of the
* algorithm in the package requested, and throw an exception if there
* is not.
*
* </ul>
*
* <p>The SecureRandom implementation attempts to completely
* randomize the internal state of the generator itself unless
* the caller follows the call to a <code>getInstance</code> method
* with a call to the <code>setSeed</code> method:
* <pre>
* SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
* random.setSeed(seed);
* </pre>
*
* <p>After the caller obtains the SecureRandom object from the
* <code>getInstance</code> call, it can call <code>nextBytes</code>
* to generate random bytes:
* <pre>
* byte bytes[] = new byte[20];
* random.nextBytes(bytes);
* </pre>
*
* <p>The caller may also invoke the <code>generateSeed</code> method
* to generate a given number of seed bytes (to seed other random number
* generators, for example):
* <pre>
* byte seed[] = random.generateSeed(20);
* </pre>
*
* @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;
/**
* <p>By using this constructor, the caller obtains a SecureRandom object
* containing the implementation from the highest-priority installed
* provider that has a SecureRandom implementation.
*
* <p>Note that this instance of SecureRandom has not been seeded.
* A call to the <code>setSeed</code> method will seed the SecureRandom
* object. If a call is not made to <code>setSeed</code>, the first call
* to the <code>nextBytes</code> method will force the SecureRandom object
* to seed itself.
*
* <p>This constructor is provided for backwards compatibility.
* The caller is encouraged to use one of the alternative
* <code>getInstance</code> methods to obtain a SecureRandom object.
*/
public SecureRandom() {
/*
* 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);
}
/**
* <p>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).
*
* <p>This constructor is provided for backwards compatibility.
* The caller is encouraged to use one of the alternative
* <code>getInstance</code> methods to obtain a SecureRandom object, and
* then to call the <code>setSeed</code> 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.
*
* <p>Note that the returned instance of SecureRandom has not been seeded.
* A call to the <code>setSeed</code> method will seed the SecureRandom
* object. If a call is not made to <code>setSeed</code>, the first call
* to the <code>nextBytes</code> method will force the SecureRandom object
* to seed itself.
*
* @param algorithm the name of the RNG algorithm.
* See Appendix A in the <a href=
* "../../../guide/security/CryptoSpec.html#AppA">
* Java Cryptography Architecture API Specification & Reference </a>
* 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.
*
* <p>Note that the returned instance of SecureRandom has not been seeded.
* A call to the <code>setSeed</code> method will seed the SecureRandom
* object. If a call is not made to <code>setSeed</code>, the first call
* to the <code>nextBytes</code> method will force the SecureRandom object
* to seed itself.
*
* @param algorithm the name of the RNG algorithm.
* See Appendix A in the <a href=
* "../../../guide/security/CryptoSpec.html#AppA">
* Java Cryptography Architecture API Specification & Reference </a>
* 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 <code>provider</code> doesn't have to be registered.
*
* <p>Note that the returned instance of SecureRandom has not been seeded.
* A call to the <code>setSeed</code> method will seed the SecureRandom
* object. If a call is not made to <code>setSeed</code>, the first call
* to the <code>nextBytes</code> method will force the SecureRandom object
* to seed itself.
*
* @param algorithm the name of the RNG algorithm.
* See Appendix A in the <a href=
* "../../../guide/security/CryptoSpec.html#AppA">
* Java Cryptography Architecture API Specification & Reference </a>
* 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 <code>provider</code> 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 <code>unknown</code> 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 <code>long seed</code>. The given seed supplements,
* rather than replaces, the existing seed. Thus, repeated calls
* are guaranteed never to reduce randomness.
*
* <p>This method is defined for compatibility with
* <code>java.util.Random</code>.
*
* @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 <code>java.util.Random</code> method, and serves
* to provide a source of random bits to all of the methods inherited
* from that class (for example, <code>nextInt</code>,
* <code>nextLong</code>, and <code>nextFloat</code>).
*
* @param numBits number of pseudo-random bits to be generated, where
* 0 <= <code>numBits</code> <= 32.
*
* @return an <code>int</code> 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.
*
* <p>This method is only included for backwards compatibility.
* The caller is encouraged to use one of the alternative
* <code>getInstance</code> methods to obtain a SecureRandom object, and
* then call the <code>generateSeed</code> 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;
}
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