/*
 * @(#)Security.java	1.132 06/07/13
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.security;

import java.lang.reflect.*;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.io.*;
import java.net.URL;
import sun.security.util.Debug;
import sun.security.util.PropertyExpander;

import java.security.Provider.Service;

import sun.security.jca.*;

/**
 * <p>This class centralizes all security properties and common security
 * methods. One of its primary uses is to manage providers.
 *
 * @author Benjamin Renaud
 * @version 1.132, 07/13/06
 */

public final class Security {
    
    /* Are we debugging? -- for developers */
    private static final Debug sdebug =
			Debug.getInstance("properties");

    /* The java.security properties */
    private static Properties props; 

    // An element in the cache
    private static class ProviderProperty {
	String className;
	Provider provider;
    }

    static {
	// doPrivileged here because there are multiple
	// things in initialize that might require privs.
	// (the FileInputStream call and the File.exists call,
	// the securityPropFile call, etc)
	AccessController.doPrivileged(new PrivilegedAction() {
	    public Object run() { 
		initialize();
		return null;
	    }
	});
    }
    
    private static void initialize() {
	props = new Properties();
	boolean loadedProps = false;
	boolean overrideAll = false;

	// first load the system properties file
	// to determine the value of security.overridePropertiesFile
	File propFile = securityPropFile("java.security");
	if (propFile.exists()) {
	    try {
		FileInputStream fis = new FileInputStream(propFile);
		InputStream is = new BufferedInputStream(fis);
		props.load(is);
		is.close();
		loadedProps = true;

		if (sdebug != null) {
		    sdebug.println("reading security properties file: " +
				propFile);
		}
	    } catch (IOException e) {
		if (sdebug != null) {
		    sdebug.println("unable to load security properties from " +
				propFile);
		    e.printStackTrace();
		}
	    }
	}

	if ("true".equalsIgnoreCase(props.getProperty
		("security.overridePropertiesFile"))) {

	    String extraPropFile = System.getProperty
					("java.security.properties");
	    if (extraPropFile != null && extraPropFile.startsWith("=")) {
		overrideAll = true;
		extraPropFile = extraPropFile.substring(1);
	    }

	    if (overrideAll) {
		props = new Properties();
		if (sdebug != null) {
		    sdebug.println
			("overriding other security properties files!");
		}
	    }

	    // now load the user-specified file so its values
	    // will win if they conflict with the earlier values
	    if (extraPropFile != null) {
		try {
		    URL propURL;

		    extraPropFile = PropertyExpander.expand(extraPropFile);
		    propFile = new File(extraPropFile);
		    if (propFile.exists()) {
			propURL = new URL
				("file:" + propFile.getCanonicalPath());
		    } else {
			propURL = new URL(extraPropFile);
		    }
		    BufferedInputStream bis = new BufferedInputStream
					(propURL.openStream());
		    props.load(bis);
		    bis.close();
		    loadedProps = true;

		    if (sdebug != null) {
			sdebug.println("reading security properties file: " +
					propURL);
			if (overrideAll) {
			    sdebug.println
				("overriding other security properties files!");
			}
		    }
		} catch (Exception e) {
		    if (sdebug != null) {
			sdebug.println
				("unable to load security properties from " +
				extraPropFile);
			e.printStackTrace();
		    }
		}
	    }
	}

	if (!loadedProps) {
	    initializeStatic();
	    if (sdebug != null) {
		sdebug.println("unable to load security properties " +
			"-- using defaults");
	    }
	}

    }
    
    /* 
     * Initialize to default values, if <java.home>/lib/java.security
     * is not found.
     */
    private static void initializeStatic() {
	props.put("security.provider.1", "sun.security.provider.Sun");
	props.put("security.provider.2", "sun.security.rsa.SunRsaSign");
	props.put("security.provider.3", "com.sun.net.ssl.internal.ssl.Provider");
	props.put("security.provider.4", "com.sun.crypto.provider.SunJCE");
	props.put("security.provider.5", "sun.security.jgss.SunProvider");
	props.put("security.provider.6", "com.sun.security.sasl.Provider");
    }

    /**
     * Don't let anyone instantiate this. 
     */
    private Security() {
    }

    private static File securityPropFile(String filename) {
	// maybe check for a system property which will specify where to
	// look. Someday.
	String sep = File.separator;
	return new File(System.getProperty("java.home") + sep + "lib" + sep + 
			"security" + sep + filename);
    }

    /**
     * Looks up providers, and returns the property (and its associated
     * provider) mapping the key, if any.
     * The order in which the providers are looked up is the
     * provider-preference order, as specificed in the security
     * properties file.
     */
    private static ProviderProperty getProviderProperty(String key) {
	ProviderProperty entry = null;

	List providers = Providers.getProviderList().providers();
	for (int i = 0; i < providers.size(); i++) {

	    String matchKey = null;
	    Provider prov = (Provider)providers.get(i);	    
	    String prop = prov.getProperty(key);

	    if (prop == null) {
		// Is there a match if we do a case-insensitive property name
		// comparison? Let's try ...
		for (Enumeration e = prov.keys();
		     e.hasMoreElements() && prop == null; ) {
		    matchKey = (String)e.nextElement();
		    if (key.equalsIgnoreCase(matchKey)) {
			prop = prov.getProperty(matchKey);
			break;
		    }
		}
	    }

	    if (prop != null) {
		ProviderProperty newEntry = new ProviderProperty();
		newEntry.className = prop;
		newEntry.provider = prov;
		return newEntry;
	    }
	}

	return entry;
    }

    /**
     * Returns the property (if any) mapping the key for the given provider.
     */
    private static String getProviderProperty(String key, Provider provider) {
	String prop = provider.getProperty(key);
	if (prop == null) {
	    // Is there a match if we do a case-insensitive property name
	    // comparison? Let's try ...
	    for (Enumeration e = provider.keys();
		 e.hasMoreElements() && prop == null; ) {
		String matchKey = (String)e.nextElement();
		if (key.equalsIgnoreCase(matchKey)) {
		    prop = provider.getProperty(matchKey);
		    break;
		}
	    }
	}
	return prop;
    }

    /** 
     * Gets a specified property for an algorithm. The algorithm name
     * should be a standard name. See Appendix A in the <a href=
     * "../../../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a> 
     * for information about standard algorithm names.
     * One possible use is by specialized algorithm parsers, which may map 
     * classes to algorithms which they understand (much like Key parsers 
     * do).
     *
     * @param algName the algorithm name.
     *
     * @param propName the name of the property to get.
     * 
     * @return the value of the specified property.  
     *
     * @deprecated This method used to return the value of a proprietary
     * property in the master file of the "SUN" Cryptographic Service
     * Provider in order to determine how to parse algorithm-specific
     * parameters. Use the new provider-based and algorithm-independent
     * <code>AlgorithmParameters</code> and <code>KeyFactory</code> engine
     * classes (introduced in the J2SE version 1.2 platform) instead.
     */
@Deprecated
    public static String getAlgorithmProperty(String algName,
					      String propName) {
	ProviderProperty entry = getProviderProperty("Alg." + propName
						     + "." + algName);
	if (entry != null) {
	    return entry.className;
	} else {
	    return null;
	}
    }

    /**
     * Adds a new provider, at a specified position. The position is
     * the preference order in which providers are searched for
     * requested algorithms.  The position is 1-based, that is,
     * 1 is most preferred, followed by 2, and so on.
     * 
     * <p>If the given provider is installed at the requested position,
     * the provider that used to be at that position, and all providers
     * with a position greater than <code>position</code>, are shifted up
     * one position (towards the end of the list of installed providers).
     * 
     * <p>A provider cannot be added if it is already installed.
     * 
     * <p>First, if there is a security manager, its
     * <code>checkSecurityAccess</code> 
     * method is called with the string
     * <code>"insertProvider."+provider.getName()</code> 
     * to see if it's ok to add a new provider. 
     * If the default implementation of <code>checkSecurityAccess</code> 
     * is used (i.e., that method is not overriden), then this will result in
     * a call to the security manager's <code>checkPermission</code> method
     * with a
     * <code>SecurityPermission("insertProvider."+provider.getName())</code>
     * permission.
     *
     * @param provider the provider to be added.
     *
     * @param position the preference position that the caller would
     * like for this provider.
     * 
     * @return the actual preference position in which the provider was 
     * added, or -1 if the provider was not added because it is
     * already installed.
     *
     * @throws  NullPointerException if provider is null
     * @throws  SecurityException
     *          if a security manager exists and its <code>{@link
     *          java.lang.SecurityManager#checkSecurityAccess}</code> method
     *          denies access to add a new provider
     *
     * @see #getProvider
     * @see #removeProvider 
     * @see java.security.SecurityPermission
     */
    public static synchronized int insertProviderAt(Provider provider, 
	    int position) {
	String providerName = provider.getName();
	check("insertProvider." + providerName);
	ProviderList list = Providers.getFullProviderList();
	ProviderList newList = ProviderList.insertAt(list, provider, position - 1);
	if (list == newList) {
	    return -1;
	}
	Providers.setProviderList(newList);
	return newList.getIndex(providerName) + 1;
    }

    /**
     * Adds a provider to the next position available.
     *
     * <p>First, if there is a security manager, its
     * <code>checkSecurityAccess</code> 
     * method is called with the string
     * <code>"insertProvider."+provider.getName()</code> 
     * to see if it's ok to add a new provider. 
     * If the default implementation of <code>checkSecurityAccess</code> 
     * is used (i.e., that method is not overriden), then this will result in
     * a call to the security manager's <code>checkPermission</code> method
     * with a
     * <code>SecurityPermission("insertProvider."+provider.getName())</code>
     * permission.
     * 
     * @param provider the provider to be added.
     *
     * @return the preference position in which the provider was 
     * added, or -1 if the provider was not added because it is
     * already installed.
     *
     * @throws  NullPointerException if provider is null
     * @throws  SecurityException
     *          if a security manager exists and its <code>{@link
     *          java.lang.SecurityManager#checkSecurityAccess}</code> method
     *          denies access to add a new provider
     * 
     * @see #getProvider
     * @see #removeProvider
     * @see java.security.SecurityPermission
     */
    public static int addProvider(Provider provider) {
	/*
 	 * We can't assign a position here because the statically
	 * registered providers may not have been installed yet. 
	 * insertProviderAt() will fix that value after it has 
	 * loaded the static providers.
 	 */
	return insertProviderAt(provider, 0);
    }

    /**
     * Removes the provider with the specified name.
     *
     * <p>When the specified provider is removed, all providers located
     * at a position greater than where the specified provider was are shifted
     * down one position (towards the head of the list of installed
     * providers).
     *
     * <p>This method returns silently if the provider is not installed or
     * if name is null.
     * 
     * <p>First, if there is a security manager, its
     * <code>checkSecurityAccess</code> 
     * method is called with the string <code>"removeProvider."+name</code> 
     * to see if it's ok to remove the provider. 
     * If the default implementation of <code>checkSecurityAccess</code> 
     * is used (i.e., that method is not overriden), then this will result in
     * a call to the security manager's <code>checkPermission</code> method
     * with a <code>SecurityPermission("removeProvider."+name)</code>
     * permission.
     *
     * @param name the name of the provider to remove.
     *
     * @throws  SecurityException
     *          if a security manager exists and its <code>{@link
     *          java.lang.SecurityManager#checkSecurityAccess}</code> method
     *          denies
     *          access to remove the provider
     *
     * @see #getProvider
     * @see #addProvider
     */
    public static synchronized void removeProvider(String name) {
	check("removeProvider." + name);
	ProviderList list = Providers.getFullProviderList();
	ProviderList newList = ProviderList.remove(list, name);
	Providers.setProviderList(newList);
    }

    /**
     * Returns an array containing all the installed providers. The order of
     * the providers in the array is their preference order.
     * 
     * @return an array of all the installed providers.
     */
    public static Provider[] getProviders() {
	return Providers.getFullProviderList().toArray();
    }

    /**
     * Returns the provider installed with the specified name, if
     * any. Returns null if no provider with the specified name is
     * installed or if name is null.
     * 
     * @param name the name of the provider to get.
     * 
     * @return the provider of the specified name.
     *
     * @see #removeProvider
     * @see #addProvider
     */
    public static Provider getProvider(String name) {
	return Providers.getProviderList().getProvider(name);
    }

    /**
     * Returns an array containing all installed providers that satisfy the
     * specified selection criterion, or null if no such providers have been
     * installed. The returned providers are ordered
     * according to their <a href=
     * "#insertProviderAt(java.security.Provider, int)">preference order</a>. 
     *  
     * <p> A cryptographic service is always associated with a particular
     * algorithm or type. For example, a digital signature service is
     * always associated with a particular algorithm (e.g., DSA),
     * and a CertificateFactory service is always associated with
     * a particular certificate type (e.g., X.509).
     *
     * <p>The selection criterion must be specified in one of the following two
     * formats:
     * <ul>
     * <li> <i>&lt;crypto_service>.&lt;algorithm_or_type></i> <p> The
     * cryptographic service name must not contain any dots.
     * <p> A 
     * provider satisfies the specified selection criterion iff the provider 
     * implements the 
     * specified algorithm or type for the specified cryptographic service.
     * <p> For example, "CertificateFactory.X.509" 
     * would be satisfied by any provider that supplied
     * a CertificateFactory implementation for X.509 certificates.
     * <li> <i>&lt;crypto_service>.&lt;algorithm_or_type> 
     * &lt;attribute_name>:&lt attribute_value></i>
     * <p> The cryptographic service name must not contain any dots. There
     * must be one or more space charaters between the the
     * <i>&lt;algorithm_or_type></i> and the <i>&lt;attribute_name></i>.
     *  <p> A provider satisfies this selection criterion iff the
     * provider implements the specified algorithm or type for the specified 
     * cryptographic service and its implementation meets the
     * constraint expressed by the specified attribute name/value pair.
     * <p> For example, "Signature.SHA1withDSA KeySize:1024" would be
     * satisfied by any provider that implemented
     * the SHA1withDSA signature algorithm with a keysize of 1024 (or larger).
     *
     * </ul>
     *
     * <p> See Appendix A in the <a href=
     * "../../../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a>
     * for information about standard cryptographic service names, standard
     * algorithm names and standard attribute names.
     *
     * @param filter the criterion for selecting
     * providers. The filter is case-insensitive.
     *
     * @return all the installed providers that satisfy the selection
     * criterion, or null if no such providers have been installed.
     *
     * @throws InvalidParameterException
     *         if the filter is not in the required format
     * @throws NullPointerException if filter is null
     *
     * @see #getProviders(java.util.Map)
     * @since 1.3
     */
    public static Provider[] getProviders(String filter) {
	String key = null;
	String value = null;
	int index = filter.indexOf(':');

	if (index == -1) {
	    key = filter;
	    value = "";
	} else {
	    key = filter.substring(0, index);
	    value = filter.substring(index + 1);
	}

	Hashtable hashtableFilter = new Hashtable(1);
	hashtableFilter.put(key, value);

	return (getProviders(hashtableFilter));
    }

    /**
     * Returns an array containing all installed providers that satisfy the 
     * specified* selection criteria, or null if no such providers have been
     * installed. The returned providers are ordered
     * according to their <a href=
     * "#insertProviderAt(java.security.Provider, int)">preference order</a>. 
     * 
     * <p>The selection criteria are represented by a map.
     * Each map entry represents a selection criterion. 
     * A provider is selected iff it satisfies all selection
     * criteria. The key for any entry in such a map must be in one of the
     * following two formats:
     * <ul>
     * <li> <i>&lt;crypto_service>.&lt;algorithm_or_type></i>
     * <p> The cryptographic service name must not contain any dots.
     * <p> The value associated with the key must be an empty string.
     * <p> A provider
     * satisfies this selection criterion iff the provider implements the 
     * specified algorithm or type for the specified cryptographic service.
     * <li>  <i>&lt;crypto_service>.&lt;algorithm_or_type> &lt;attribute_name></i>
     * <p> The cryptographic service name must not contain any dots. There
     * must be one or more space charaters between the <i>&lt;algorithm_or_type></i>
     * and the <i>&lt;attribute_name></i>.
     * <p> The value associated with the key must be a non-empty string.
     * A provider satisfies this selection criterion iff the
     * provider implements the specified algorithm or type for the specified 
     * cryptographic service and its implementation meets the
     * constraint expressed by the specified attribute name/value pair. 
     * </ul>
     *
     * <p> See Appendix A in the <a href=
     * "../../../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a>
     * for information about standard cryptographic service names, standard
     * algorithm names and standard attribute names.
     *
     * @param filter the criteria for selecting
     * providers. The filter is case-insensitive.
     *
     * @return all the installed providers that satisfy the selection
     * criteria, or null if no such providers have been installed. 
     *
     * @throws InvalidParameterException
     *         if the filter is not in the required format
     * @throws NullPointerException if filter is null
     *
     * @see #getProviders(java.lang.String)
     * @since 1.3
     */
    public static Provider[] getProviders(Map<String,String> filter) {
	// Get all installed providers first.
	// Then only return those providers who satisfy the selection criteria.
	Provider[] allProviders = Security.getProviders();
	Set keySet = filter.keySet();
	LinkedHashSet candidates = new LinkedHashSet(5);

	// Returns all installed providers
	// if the selection criteria is null.
	if ((keySet == null) || (allProviders == null)) {
	    return allProviders;
	}
	
	boolean firstSearch = true;

	// For each selection criterion, remove providers
	// which don't satisfy the criterion from the candidate set.
	for (Iterator ite = keySet.iterator(); ite.hasNext(); ) {
	    String key = (String)ite.next();
	    String value = (String)filter.get(key);
	    
	    LinkedHashSet newCandidates = getAllQualifyingCandidates(key, value, 
							       allProviders);
	    if (firstSearch) {
		candidates = newCandidates;
		firstSearch = false;
	    }

	    if ((newCandidates != null) && !newCandidates.isEmpty()) {
		// For each provider in the candidates set, if it
		// isn't in the newCandidate set, we should remove
		// it from the candidate set.
		for (Iterator cansIte = candidates.iterator();
		     cansIte.hasNext(); ) {
		    Provider prov = (Provider)cansIte.next();
		    if (!newCandidates.contains(prov)) {
			cansIte.remove();
		    }
		}
	    } else {
		candidates = null;
		break;
	    }
	}

	if ((candidates == null) || (candidates.isEmpty()))
	    return null;

	Object[] candidatesArray = candidates.toArray();
	Provider[] result = new Provider[candidatesArray.length];

	for (int i = 0; i < result.length; i++) {
	    result[i] = (Provider)candidatesArray[i];
	}
	
	return result;
    }
    
    // Map containing cached Spi Class objects of the specified type
    private static final Map<String,Class> spiMap = 
				new ConcurrentHashMap<String,Class>();
    
    /**
     * Return the Class object for the given engine type 
     * (e.g. "MessageDigest"). Works for Spis in the java.security package
     * only.
     */
    private static Class getSpiClass(String type) {
	Class clazz = spiMap.get(type);
	if (clazz != null) {
	    return clazz;
	}
	try {
	    clazz = Class.forName("java.security." + type + "Spi");
	    spiMap.put(type, clazz);
	    return clazz;
	} catch (ClassNotFoundException e) {
	    throw (Error)new AssertionError("Spi class not found").initCause(e);
	}
    }

    /*
     * Returns an array of objects: the first object in the array is
     * an instance of an implementation of the requested algorithm
     * and type, and the second object in the array identifies the provider
     * of that implementation.
     * The <code>provider</code> argument can be null, in which case all
     * configured providers will be searched in order of preference.
     */
    static Object[] getImpl(String algorithm, String type, String provider)
	    throws NoSuchAlgorithmException, NoSuchProviderException {
	if (provider == null) {
	    return GetInstance.getInstance
	    	(type, getSpiClass(type), algorithm).toArray();
	} else {
	    return GetInstance.getInstance
	    	(type, getSpiClass(type), algorithm, provider).toArray();
	}
    }

    static Object[] getImpl(String algorithm, String type, String provider,
	    Object params) throws NoSuchAlgorithmException, 
	    NoSuchProviderException, InvalidAlgorithmParameterException {
	if (provider == null) {
	    return GetInstance.getInstance
	    	(type, getSpiClass(type), algorithm, params).toArray();
	} else {
	    return GetInstance.getInstance
	    	(type, getSpiClass(type), algorithm, params, provider).toArray();
	}
    }

    /*
     * Returns an array of objects: the first object in the array is
     * an instance of an implementation of the requested algorithm
     * and type, and the second object in the array identifies the provider
     * of that implementation.
     * The <code>provider</code> argument cannot be null.
     */
    static Object[] getImpl(String algorithm, String type, Provider provider)
	    throws NoSuchAlgorithmException {
	return GetInstance.getInstance
	    (type, getSpiClass(type), algorithm, provider).toArray();
    }

    static Object[] getImpl(String algorithm, String type, Provider provider,
	    Object params) throws NoSuchAlgorithmException, 
	    InvalidAlgorithmParameterException {
	return GetInstance.getInstance
	    (type, getSpiClass(type), algorithm, params, provider).toArray();
    }

    /**
     * Gets a security property value.
     *
     * <p>First, if there is a security manager, its
     * <code>checkPermission</code>  method is called with a 
     * <code>java.security.SecurityPermission("getProperty."+key)</code>
     * permission to see if it's ok to retrieve the specified
     * security property value.. 
     *
     * @param key the key of the property being retrieved.
     *
     * @return the value of the security property corresponding to key.
     *
     * @throws  SecurityException
     *          if a security manager exists and its <code>{@link
     *          java.lang.SecurityManager#checkPermission}</code> method
     *          denies
     *          access to retrieve the specified security property value
     * @throws  NullPointerException is key is null
     * 
     * @see #setProperty
     * @see java.security.SecurityPermission
     */
    public static String getProperty(String key) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    sm.checkPermission(new SecurityPermission("getProperty."+
						      key));
	}
	String name = props.getProperty(key);
	if (name != null)
	    name = name.trim();	// could be a class name with trailing ws
	return name;
    }

    /**
     * Sets a security property value.
     *
     * <p>First, if there is a security manager, its
     * <code>checkPermission</code> method is called with a 
     * <code>java.security.SecurityPermission("setProperty."+key)</code>
     * permission to see if it's ok to set the specified
     * security property value.
     *
     * @param key the name of the property to be set.
     *
     * @param datum the value of the property to be set.
     *
     * @throws  SecurityException
     *          if a security manager exists and its <code>{@link
     *          java.lang.SecurityManager#checkPermission}</code> method
     *          denies access to set the specified security property value
     * @throws  NullPointerException if key or datum is null
     * 
     * @see #getProperty
     * @see java.security.SecurityPermission
     */
    public static void setProperty(String key, String datum) {
	check("setProperty."+key);
	props.put(key, datum);
	invalidateSMCache(key);  /* See below. */
    }

    /*
     * Implementation detail:  If the property we just set in
     * setProperty() was either "package.access" or
     * "package.definition", we need to signal to the SecurityManager
     * class that the value has just changed, and that it should
     * invalidate it's local cache values.
     *
     * Rather than create a new API entry for this function,
     * we use reflection to set a private variable.
     */
    private static void invalidateSMCache(String key) {
	
	final boolean pa = key.equals("package.access");
	final boolean pd = key.equals("package.definition");

	if (pa || pd) {
	    AccessController.doPrivileged(new PrivilegedAction() {
		public Object run() {
		    try {
			/* Get the class via the bootstrap class loader. */
			Class cl = Class.forName(
			    "java.lang.SecurityManager", false, null);
			Field f = null;
			boolean accessible = false;

			if (pa) {
			    f = cl.getDeclaredField("packageAccessValid");
			    accessible = f.isAccessible();
			    f.setAccessible(true);
			} else {
			    f = cl.getDeclaredField("packageDefinitionValid");
			    accessible = f.isAccessible();
			    f.setAccessible(true);
			}
			f.setBoolean(f, false);
			f.setAccessible(accessible);
		    }
		    catch (Exception e1) {
			/* If we couldn't get the class, it hasn't
			 * been loaded yet.  If there is no such
			 * field, we shouldn't try to set it.  There
			 * shouldn't be a security execption, as we
			 * are loaded by boot class loader, and we
			 * are inside a doPrivileged() here.
			 *
			 * NOOP: don't do anything...
			 */
		    }
		    return null;
		}  /* run */
	    });  /* PrivilegedAction */
	}  /* if */
    }

    private static void check(String directive) {	
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkSecurityAccess(directive);
	}
    }
    
    /*
    * Returns all providers who satisfy the specified
    * criterion.
    */
    private static LinkedHashSet getAllQualifyingCandidates(String filterKey,
						 String filterValue,
						 Provider[] allProviders) {
	String[] filterComponents = getFilterComponents(filterKey,
							filterValue);

	// The first component is the service name.
	// The second is the algorithm name.
	// If the third isn't null, that is the attrinute name.
	String serviceName = filterComponents[0];
	String algName = filterComponents[1];
	String attrName = filterComponents[2];

	return getProvidersNotUsingCache(serviceName, algName, attrName,
					 filterValue, allProviders);
    }
	
    private static LinkedHashSet getProvidersNotUsingCache(String serviceName,
						     String algName,
						     String attrName,
						     String filterValue,
						     Provider[] allProviders) {
	LinkedHashSet candidates = new LinkedHashSet(5);
	for (int i = 0; i < allProviders.length; i++) {
	    if (isCriterionSatisfied(allProviders[i], serviceName, 
				     algName,
				     attrName, filterValue)) {
		candidates.add(allProviders[i]);
	    }
	}
	return candidates;
    }

    /*
     * Returns true if the given provider satisfies
     * the selection criterion key:value.
     */
    private static boolean isCriterionSatisfied(Provider prov, 
						String serviceName,
						String algName,
						String attrName,
						String filterValue) {
	String key = serviceName + '.' + algName;

	if (attrName != null) {
	    key += ' ' + attrName;
	}
      	// Check whether the provider has a property
	// whose key is the same as the given key.
	String propValue = getProviderProperty(key, prov);

	if (propValue == null) {
	    // Check whether we have an alias instead
	    // of a standard name in the key.
	    String standardName = getProviderProperty("Alg.Alias." + 
						      serviceName + "." +
						      algName,
						      prov);
	    if (standardName != null) {
		key = serviceName + "." + standardName;

		if (attrName != null) {
		    key += ' ' + attrName;
		}

		propValue = getProviderProperty(key, prov);
	    }
	    
	    if (propValue == null) {
		// The provider doesn't have the given
		// key in its property list.
		return false;
	    }
	}

	// If the key is in the format of:
	// <crypto_service>.<algorithm_or_type>,
        // there is no need to check the value.
	
	if (attrName == null) {
	    return true;
	}

	// If we get here, the key must be in the
	// format of <crypto_service>.<algorithm_or_provider> <attribute_name>.
	if (isStandardAttr(attrName)) {
	    return isConstraintSatisfied(attrName, filterValue, propValue);
	} else {
	    return filterValue.equalsIgnoreCase(propValue);
	}
    }
	    
    /*
     * Returns true if the attribute is a standard attribute;
     * otherwise, returns false.
     */
    private static boolean isStandardAttr(String attribute) {
	// For now, we just have two standard attributes: 
	// KeySize and ImplementedIn.
	if (attribute.equalsIgnoreCase("KeySize"))
	    return true;
	
	if (attribute.equalsIgnoreCase("ImplementedIn"))
	    return true;

	return false;
    }

    /*
     * Returns true if the requested attribute value is supported;
     * otherwise, returns false.
     */
    private static boolean isConstraintSatisfied(String attribute,
						 String value,
						 String prop) {
	// For KeySize, prop is the max key size the
	// provider supports for a specific <crypto_service>.<algorithm>.
	if (attribute.equalsIgnoreCase("KeySize")) {
	    int requestedSize = Integer.parseInt(value);
	    int maxSize = Integer.parseInt(prop);
	    if (requestedSize <= maxSize) {
		return true;
	    } else {
		return false;
	    }
	}

	// For Type, prop is the type of the implementation
	// for a specific <crypto service>.<algorithm>.
	if (attribute.equalsIgnoreCase("ImplementedIn")) {
	    return value.equalsIgnoreCase(prop);
	}

	return false;
    }

    static String[] getFilterComponents(String filterKey, String filterValue) {
	int algIndex = filterKey.indexOf('.');

	if (algIndex < 0) {
	    // There must be a dot in the filter, and the dot
	    // shouldn't be at the beginning of this string.
	    throw new InvalidParameterException("Invalid filter");
	}

	String serviceName = filterKey.substring(0, algIndex);
	String algName = null;
	String attrName = null;

	if (filterValue.length() == 0) {
	    // The filterValue is an empty string. So the filterKey 
	    // should be in the format of <crypto_service>.<algorithm_or_type>.
	    algName = filterKey.substring(algIndex + 1).trim();
	    if (algName.length() == 0) {
		// There must be a algorithm or type name.
		throw new InvalidParameterException("Invalid filter");
	    }
	} else {	
	    // The filterValue is a non-empty string. So the filterKey must be
	    // in the format of
	    // <crypto_service>.<algorithm_or_type> <attribute_name>
	    int attrIndex = filterKey.indexOf(' ');

	    if (attrIndex == -1) {
		// There is no attribute name in the filter.
		throw new InvalidParameterException("Invalid filter");
	    } else {
		attrName = filterKey.substring(attrIndex + 1).trim();
		if (attrName.length() == 0) {
		    // There is no attribute name in the filter.
		    throw new InvalidParameterException("Invalid filter");
		}
	    }
	
	    // There must be an algorithm name in the filter.
	    if ((attrIndex < algIndex) ||
		(algIndex == attrIndex - 1)) {
		throw new InvalidParameterException("Invalid filter");
	    } else {
		algName = filterKey.substring(algIndex + 1, attrIndex);
	    }
	}

	String[] result = new String[3];
	result[0] = serviceName;
	result[1] = algName;
	result[2] = attrName;

	return result;
    }

    /**
     * Returns a Set of Strings containing the names of all available
     * algorithms or types for the specified Java cryptographic service
     * (e.g., Signature, MessageDigest, Cipher, Mac, KeyStore). Returns
     * an empty Set if there is no provider that supports the  
     * specified service or if serviceName is null. For a complete list 
     * of Java cryptographic services, please see the 
     * <a href="../../../technotes/guides/security/crypto/CryptoSpec.html">Java 
     * Cryptography Architecture API Specification &amp; Reference</a>.
     * Note: the returned set is immutable.
     *
     * @param serviceName the name of the Java cryptographic 
     * service (e.g., Signature, MessageDigest, Cipher, Mac, KeyStore).
     * Note: this parameter is case-insensitive.
     *
     * @return a Set of Strings containing the names of all available 
     * algorithms or types for the specified Java cryptographic service
     * or an empty set if no provider supports the specified service.
     *
     * @since 1.4
     **/
    public static Set<String> getAlgorithms(String serviceName) {

	if ((serviceName == null) || (serviceName.length() == 0) ||
	    (serviceName.endsWith("."))) {
	    return Collections.EMPTY_SET;
	}

	HashSet result = new HashSet();
	Provider[] providers = Security.getProviders();

	for (int i = 0; i < providers.length; i++) {
	    // Check the keys for each provider.
	    for (Enumeration e = providers[i].keys(); e.hasMoreElements(); ) {
		String currentKey = ((String)e.nextElement()).toUpperCase();
		if (currentKey.startsWith(serviceName.toUpperCase())) {
		    // We should skip the currentKey if it contains a 
		    // whitespace. The reason is: such an entry in the
		    // provider property contains attributes for the
		    // implementation of an algorithm. We are only interested
		    // in entries which lead to the implementation
		    // classes.
		    if (currentKey.indexOf(" ") < 0) {
			result.add(currentKey.substring(serviceName.length() + 1));
		    }
		}
	    }	    
	}
	return Collections.unmodifiableSet(result);
    }
}