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      1 /*
      2  * Copyright (C) 2007 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.security;
     18 
     19 import java.security.NoSuchAlgorithmException;
     20 
     21 /**
     22  * Base class for producing a message digest from different hash encryptions.
     23  */
     24 public abstract class MessageDigest
     25 {
     26     /**
     27      * Returns a digest object of the specified type.
     28      *
     29      * @param algorithm  The type of hash function to use. Valid values are
     30      *                   <em>SHA-1</em> and <em>MD5</em>.
     31      * @return The respective MessageDigest object. Either a
     32      *         {@link android.security.Sha1MessageDigest} or
     33      *         {@link android.security.Md5MessageDigest} object.
     34      * @throws NoSuchAlgorithmException If an invalid <var>algorithm</var>
     35      *                                  is given.
     36      */
     37     public static MessageDigest getInstance(String algorithm)
     38         throws NoSuchAlgorithmException
     39     {
     40         if (algorithm == null) {
     41             return null;
     42         }
     43 
     44         if (algorithm.equals("SHA-1")) {
     45             return new Sha1MessageDigest();
     46         }
     47         else if (algorithm.equals("MD5")) {
     48             return new Md5MessageDigest();
     49         }
     50 
     51         throw new NoSuchAlgorithmException();
     52     }
     53 
     54     public abstract void update(byte[] input);
     55     public abstract byte[] digest();
     56 
     57     /**
     58      * Produces a message digest for the given input.
     59      *
     60      * @param input  The message to encrypt.
     61      * @return The digest (hash sum).
     62      */
     63     public abstract byte[] digest(byte[] input);
     64 }
     65