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+/* ExemptionMechanism.java -- Generic crypto-weakening mechanism.
+   Copyright (C) 2004  Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package javax.crypto;
+
+import gnu.java.security.Engine;
+
+import java.lang.reflect.InvocationTargetException;
+import java.security.AlgorithmParameters;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.Key;
+import java.security.NoSuchAlgorithmException;
+import java.security.NoSuchProviderException;
+import java.security.Provider;
+import java.security.Security;
+import java.security.spec.AlgorithmParameterSpec;
+
+/**
+ * An exemption mechanism, which will conditionally allow cryptography
+ * where it is not normally allowed, implements things such as <i>key
+ * recovery</i>, <i>key weakening</i>, or <i>key escrow</i>.
+ *
+ * <p><b>Implementation note</b>: this class is present for
+ * API-compatibility only; it is not actually used anywhere in this library
+ * and this library does not, in general, support crypto weakening.
+ *
+ * @author Casey Marshall (csm@gnu.org)
+ * @since 1.4
+ */
+public class ExemptionMechanism
+{
+
+  // Constants and fields.
+  // ------------------------------------------------------------------------
+
+  private static final String SERVICE = "ExemptionMechanism";
+  private ExemptionMechanismSpi emSpi;
+  private Provider provider;
+  private String mechanism;
+  private boolean virgin;
+
+  // Constructor.
+  // ------------------------------------------------------------------------
+
+  protected ExemptionMechanism(ExemptionMechanismSpi emSpi, Provider provider,
+                               String mechanism)
+  {
+    this.emSpi = emSpi;
+    this.provider = provider;
+    this.mechanism = mechanism;
+    virgin = true;
+  }
+
+  /**
+   * Create an instance of <code>ExemptionMechanism</code> for a designated
+   * <code>mechanism</code> from the first Security Provider offering it.
+   *
+   * @param mechanism the name of the exemption mechanism to create.
+   * @return a newly created instance of <code>ExemptionMechanism</code>.
+   * @throws IllegalArgumentException if the provider is null.
+   * @throws NoSuchAlgorithmException if no such exemption mechanism is
+   *           available from any known Security Provider.
+   * @throws IllegalArgumentException if <code>mechanism</code> is
+   *           <code>null</code> or is an empty string.
+   */
+  public static final ExemptionMechanism getInstance(String mechanism)
+      throws NoSuchAlgorithmException
+  {
+    Provider[] p = Security.getProviders();
+    NoSuchAlgorithmException lastException = null;
+    for (int i = 0; i < p.length; i++)
+      try
+        {
+          return getInstance(mechanism, p[i]);
+        }
+      catch (NoSuchAlgorithmException x)
+        {
+          lastException = x;
+        }
+    if (lastException != null)
+      throw lastException;
+    throw new NoSuchAlgorithmException(mechanism);
+  }
+
+  /**
+   * Create an instance of <code>ExemptionMechanism</code> for a designated
+   * <code>mechanism</code> from a named <code>provider</code>.
+   *
+   * @param mechanism the name of the exemption mechanism to create.
+   * @param provider the security provider to provide the exemption
+   *          <code>mechanism</code>.
+   * @return a newly created instance of <code>ExemptionMechanism</code>.
+   * @throws NoSuchAlgorithmException if no such exemption mechanism is
+   *           available from the named <code>provider</code>.
+   * @throws NoSuchProviderException if no Security Provider with the designated
+   *           name is known to the underlying JVM.
+   * @throws IllegalArgumentException if either <code>mechanism</code> or
+   *           <code>provider</code> is <code>null</code>, or if
+   *           <code>mechanism</code> is an empty string.
+   */
+  public static final ExemptionMechanism getInstance(String mechanism,
+                                                     String provider)
+      throws NoSuchAlgorithmException, NoSuchProviderException
+  {
+    if (provider == null)
+      throw new IllegalArgumentException("provider MUST NOT be null");
+    Provider p = Security.getProvider(provider);
+    if (p == null)
+      throw new NoSuchProviderException(provider);
+    return getInstance(mechanism, p);
+  }
+
+  /**
+   * Create an instance of <code>ExemptionMechanism</code> for a designated
+   * <code>mechanism</code> from a designated <code>provider</code>.
+   *
+   * @param mechanism the name of the exemption mechanism to create.
+   * @param provider the security provider to provide the exemption
+   *          <code>mechanism</code>.
+   * @return a newly created instance of <code>ExemptionMechanism</code>.
+   * @throws NoSuchAlgorithmException if an exemption mechanism could not be
+   *           created.
+   * @throws IllegalArgumentException if either <code>mechanism</code> or
+   *           <code>provider</code> is <code>null</code>, or if
+   *           <code>mechanism</code> is an empty string.
+   */
+  public static final ExemptionMechanism getInstance(String mechanism,
+                                                     Provider provider)
+      throws NoSuchAlgorithmException
+  {
+    StringBuilder sb = new StringBuilder("ExemptionMechanism [")
+        .append(mechanism).append("] from provider[")
+        .append(provider).append("] could not be created");
+    Throwable cause;
+    try
+      {
+        Object spi = Engine.getInstance(SERVICE, mechanism, provider);
+        return new ExemptionMechanism((ExemptionMechanismSpi) spi,
+                                      provider,
+                                      mechanism);
+      }
+    catch (InvocationTargetException x)
+      {
+        cause = x.getCause();
+        if (cause instanceof NoSuchAlgorithmException)
+          throw (NoSuchAlgorithmException) cause;
+        if (cause == null)
+          cause = x;
+      }
+    catch (ClassCastException x)
+      {
+        cause = x;
+      }
+    NoSuchAlgorithmException x = new NoSuchAlgorithmException(sb.toString());
+    x.initCause(cause);
+    throw x;
+  }
+
+  public final byte[] genExemptionBlob()
+    throws IllegalStateException, ExemptionMechanismException
+  {
+    if (virgin)
+      {
+        throw new IllegalStateException("not initialized");
+      }
+    return emSpi.engineGenExemptionBlob();
+  }
+
+  public final int genExemptionBlob(byte[] output)
+    throws IllegalStateException, ExemptionMechanismException,
+           ShortBufferException
+  {
+    return genExemptionBlob(output, 0);
+  }
+
+  public final int genExemptionBlob(byte[] output, int outputOffset)
+    throws IllegalStateException, ExemptionMechanismException,
+           ShortBufferException
+  {
+    if (virgin)
+      {
+        throw new IllegalStateException("not initialized");
+      }
+    return emSpi.engineGenExemptionBlob(output, outputOffset);
+  }
+
+  public final String getName()
+  {
+    return mechanism;
+  }
+
+  public final int getOutputSize(int inputLength) throws IllegalStateException
+  {
+    if (virgin)
+      {
+        throw new IllegalStateException("not initialized");
+      }
+    return emSpi.engineGetOutputSize(inputLength);
+  }
+
+  public final Provider getProvider()
+  {
+    return provider;
+  }
+
+  public final void init(Key key)
+    throws ExemptionMechanismException, InvalidKeyException
+  {
+    emSpi.engineInit(key);
+    virgin = false;
+  }
+
+  public final void init(Key key, AlgorithmParameters params)
+    throws ExemptionMechanismException, InvalidAlgorithmParameterException,
+           InvalidKeyException
+  {
+    emSpi.engineInit(key, params);
+    virgin = false;
+  }
+
+  public final void init(Key key, AlgorithmParameterSpec params)
+    throws ExemptionMechanismException, InvalidAlgorithmParameterException,
+           InvalidKeyException
+  {
+    emSpi.engineInit(key, params);
+    virgin = false;
+  }
+
+  public final boolean isCryptoAllowed(Key key)
+    throws ExemptionMechanismException
+  {
+    return true;
+  }
+
+  protected void finalize()
+  {
+  }
+}