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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code 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
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package java.security.spec;
  
  import java.security.spec.AlgorithmParameterSpec;
  
  /**
   * This class specifies the set of parameters used with mask generation
   * function MGF1 in OAEP Padding and RSA-PSS signature scheme, as
   * defined in the
   * <a href="http://www.ietf.org/rfc/rfc3447.txt">PKCS #1 v2.1</a>
   * standard.
   *
   * <p>Its ASN.1 definition in PKCS#1 standard is described below:
   * <pre>
   * MGF1Parameters ::= OAEP-PSSDigestAlgorthms
   * </pre>
   * where
   * <pre>
   * OAEP-PSSDigestAlgorithms    ALGORITHM-IDENTIFIER ::= {
   *   { OID id-sha1 PARAMETERS NULL   }|
   *   { OID id-sha224 PARAMETERS NULL   }|
   *   { OID id-sha256 PARAMETERS NULL }|
   *   { OID id-sha384 PARAMETERS NULL }|
   *   { OID id-sha512 PARAMETERS NULL },
   *   ...  -- Allows for future expansion --
   * }
   * </pre>
   * @see PSSParameterSpec
   * @see javax.crypto.spec.OAEPParameterSpec
   *
   * @author Valerie Peng
   *
   * @since 1.5
   */
  public class MGF1ParameterSpec implements AlgorithmParameterSpec {
  
      /**
       * The MGF1ParameterSpec which uses "SHA-1" message digest.
       */
      public static final MGF1ParameterSpec SHA1 =
          new MGF1ParameterSpec("SHA-1");
      /**
       * The MGF1ParameterSpec which uses "SHA-224" message digest.
       */
      public static final MGF1ParameterSpec SHA224 =
          new MGF1ParameterSpec("SHA-224");
      /**
       * The MGF1ParameterSpec which uses "SHA-256" message digest.
       */
      public static final MGF1ParameterSpec SHA256 =
          new MGF1ParameterSpec("SHA-256");
      /**
       * The MGF1ParameterSpec which uses "SHA-384" message digest.
       */
      public static final MGF1ParameterSpec SHA384 =
          new MGF1ParameterSpec("SHA-384");
      /**
       * The MGF1ParameterSpec which uses SHA-512 message digest.
       */
      public static final MGF1ParameterSpec SHA512 =
          new MGF1ParameterSpec("SHA-512");
  
      private String mdName;
  
      /**
       * Constructs a parameter set for mask generation function MGF1
       * as defined in the PKCS #1 standard.
       *
       * @param mdName the algorithm name for the message digest
       * used in this mask generation function MGF1.
       * @exception NullPointerException if {@code mdName} is null.
       */
      public MGF1ParameterSpec(String mdName) {
          if (mdName == null) {
              throw new NullPointerException("digest algorithm is null");
          }
          this.mdName = mdName;
      }
  
      /**
       * Returns the algorithm name of the message digest used by the mask
       * generation function.
       *
       * @return the algorithm name of the message digest.
       */
      public String getDigestAlgorithm() {
          return mdName;
      }
  }
  