MD5算法--Java类MessageDigest实现

  1 /*
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  3  * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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 24  */
 25 
 26 package java.security;
 27 
 28 import java.util.*;
 29 import java.lang.*;
 30 import java.io.IOException;
 31 import java.io.ByteArrayOutputStream;
 32 import java.io.PrintStream;
 33 import java.io.InputStream;
 34 import java.io.ByteArrayInputStream;
 35 
 36 import java.nio.ByteBuffer;
 37 
 38 /**
 39  * This MessageDigest class provides applications the functionality of a
 40  * message digest algorithm, such as SHA-1 or SHA-256.
 41  * Message digests are secure one-way hash functions that take arbitrary-sized
 42  * data and output a fixed-length hash value.
 43  *
 44  * <p>A MessageDigest object starts out initialized. The data is
 45  * processed through it using the {@link #update(byte) update}
 46  * methods. At any point {@link #reset() reset} can be called
 47  * to reset the digest. Once all the data to be updated has been
 48  * updated, one of the {@link #digest() digest} methods should
 49  * be called to complete the hash computation.
 50  *
 51  * <p>The <code>digest</code> method can be called once for a given number
 52  * of updates. After <code>digest</code> has been called, the MessageDigest
 53  * object is reset to its initialized state.
 54  *
 55  * <p>Implementations are free to implement the Cloneable interface.
 56  * Client applications can test cloneability by attempting cloning
 57  * and catching the CloneNotSupportedException: <p>
 58  *
 59 * <pre>
 60 * MessageDigest md = MessageDigest.getInstance("SHA");
 61 *
 62 * try {
 63 *     md.update(toChapter1);
 64 *     MessageDigest tc1 = md.clone();
 65 *     byte[] toChapter1Digest = tc1.digest();
 66 *     md.update(toChapter2);
 67 *     ...etc.
 68 * } catch (CloneNotSupportedException cnse) {
 69 *     throw new DigestException("couldn‘t make digest of partial content");
 70 * }
 71 * </pre>
 72  *
 73  * <p>Note that if a given implementation is not cloneable, it is
 74  * still possible to compute intermediate digests by instantiating
 75  * several instances, if the number of digests is known in advance.
 76  *
 77  * <p>Note that this class is abstract and extends from
 78  * <code>MessageDigestSpi</code> for historical reasons.
 79  * Application developers should only take notice of the methods defined in
 80  * this <code>MessageDigest</code> class; all the methods in
 81  * the superclass are intended for cryptographic service providers who wish to
 82  * supply their own implementations of message digest algorithms.
 83  *
 84  * <p> Every implementation of the Java platform is required to support
 85  * the following standard <code>MessageDigest</code> algorithms:
 86  * <ul>
 87  * <li><tt>MD5</tt></li>
 88  * <li><tt>SHA-1</tt></li>
 89  * <li><tt>SHA-256</tt></li>
 90  * </ul>
 91  * These algorithms are described in the <a href=
 92  * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">
 93  * MessageDigest section</a> of the
 94  * Java Cryptography Architecture Standard Algorithm Name Documentation.
 95  * Consult the release documentation for your implementation to see if any
 96  * other algorithms are supported.
 97  *
 98  * @author Benjamin Renaud
 99  *
100  * @see DigestInputStream
101  * @see DigestOutputStream
102  */
103 
104 public abstract class MessageDigest extends MessageDigestSpi {
105 
106     private String algorithm;
107 
108     // The state of this digest
109     private static final int INITIAL = 0;
110     private static final int IN_PROGRESS = 1;
111     private int state = INITIAL;
112 
113     // The provider
114     private Provider provider;
115 
116     /**
117      * Creates a message digest with the specified algorithm name.
118      *
119      * @param algorithm the standard name of the digest algorithm.
120      * See the MessageDigest section in the <a href=
121      * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">
122      * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
123      * for information about standard algorithm names.
124      */
125     protected MessageDigest(String algorithm) {
126         this.algorithm = algorithm;
127     }
128 
129     /**
130      * Returns a MessageDigest object that implements the specified digest
131      * algorithm.
132      *
133      * <p> This method traverses the list of registered security Providers,
134      * starting with the most preferred Provider.
135      * A new MessageDigest object encapsulating the
136      * MessageDigestSpi implementation from the first
137      * Provider that supports the specified algorithm is returned.
138      *
139      * <p> Note that the list of registered providers may be retrieved via
140      * the {@link Security#getProviders() Security.getProviders()} method.
141      *
142      * @param algorithm the name of the algorithm requested.
143      * See the MessageDigest section in the <a href=
144      * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">
145      * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
146      * for information about standard algorithm names.
147      *
148      * @return a Message Digest object that implements the specified algorithm.
149      *
150      * @exception NoSuchAlgorithmException if no Provider supports a
151      *          MessageDigestSpi implementation for the
152      *          specified algorithm.
153      *
154      * @see Provider
155      */
156     public static MessageDigest getInstance(String algorithm)
157     throws NoSuchAlgorithmException {
158         try {
159             Object[] objs = Security.getImpl(algorithm, "MessageDigest",
160                                              (String)null);
161             if (objs[0] instanceof MessageDigest) {
162                 MessageDigest md = (MessageDigest)objs[0];
163                 md.provider = (Provider)objs[1];
164                 return md;
165             } else {
166                 MessageDigest delegate =
167                     new Delegate((MessageDigestSpi)objs[0], algorithm);
168                 delegate.provider = (Provider)objs[1];
169                 return delegate;
170             }
171         } catch(NoSuchProviderException e) {
172             throw new NoSuchAlgorithmException(algorithm + " not found");
173         }
174     }
175 
176     /**
177      * Returns a MessageDigest object that implements the specified digest
178      * algorithm.
179      *
180      * <p> A new MessageDigest object encapsulating the
181      * MessageDigestSpi implementation from the specified provider
182      * is returned.  The specified provider must be registered
183      * in the security provider list.
184      *
185      * <p> Note that the list of registered providers may be retrieved via
186      * the {@link Security#getProviders() Security.getProviders()} method.
187      *
188      * @param algorithm the name of the algorithm requested.
189      * See the MessageDigest section in the <a href=
190      * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">
191      * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
192      * for information about standard algorithm names.
193      *
194      * @param provider the name of the provider.
195      *
196      * @return a MessageDigest object that implements the specified algorithm.
197      *
198      * @exception NoSuchAlgorithmException if a MessageDigestSpi
199      *          implementation for the specified algorithm is not
200      *          available from the specified provider.
201      *
202      * @exception NoSuchProviderException if the specified provider is not
203      *          registered in the security provider list.
204      *
205      * @exception IllegalArgumentException if the provider name is null
206      *          or empty.
207      *
208      * @see Provider
209      */
210     public static MessageDigest getInstance(String algorithm, String provider)
211         throws NoSuchAlgorithmException, NoSuchProviderException
212     {
213         if (provider == null || provider.length() == 0)
214             throw new IllegalArgumentException("missing provider");
215         Object[] objs = Security.getImpl(algorithm, "MessageDigest", provider);
216         if (objs[0] instanceof MessageDigest) {
217             MessageDigest md = (MessageDigest)objs[0];
218             md.provider = (Provider)objs[1];
219             return md;
220         } else {
221             MessageDigest delegate =
222                 new Delegate((MessageDigestSpi)objs[0], algorithm);
223             delegate.provider = (Provider)objs[1];
224             return delegate;
225         }
226     }
227 
228     /**
229      * Returns a MessageDigest object that implements the specified digest
230      * algorithm.
231      *
232      * <p> A new MessageDigest object encapsulating the
233      * MessageDigestSpi implementation from the specified Provider
234      * object is returned.  Note that the specified Provider object
235      * does not have to be registered in the provider list.
236      *
237      * @param algorithm the name of the algorithm requested.
238      * See the MessageDigest section in the <a href=
239      * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">
240      * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
241      * for information about standard algorithm names.
242      *
243      * @param provider the provider.
244      *
245      * @return a MessageDigest object that implements the specified algorithm.
246      *
247      * @exception NoSuchAlgorithmException if a MessageDigestSpi
248      *          implementation for the specified algorithm is not available
249      *          from the specified Provider object.
250      *
251      * @exception IllegalArgumentException if the specified provider is null.
252      *
253      * @see Provider
254      *
255      * @since 1.4
256      */
257     public static MessageDigest getInstance(String algorithm,
258                                             Provider provider)
259         throws NoSuchAlgorithmException
260     {
261         if (provider == null)
262             throw new IllegalArgumentException("missing provider");
263         Object[] objs = Security.getImpl(algorithm, "MessageDigest", provider);
264         if (objs[0] instanceof MessageDigest) {
265             MessageDigest md = (MessageDigest)objs[0];
266             md.provider = (Provider)objs[1];
267             return md;
268         } else {
269             MessageDigest delegate =
270                 new Delegate((MessageDigestSpi)objs[0], algorithm);
271             delegate.provider = (Provider)objs[1];
272             return delegate;
273         }
274     }
275 
276     /**
277      * Returns the provider of this message digest object.
278      *
279      * @return the provider of this message digest object
280      */
281     public final Provider getProvider() {
282         return this.provider;
283     }
284 
285     /**
286      * Updates the digest using the specified byte.
287      *
288      * @param input the byte with which to update the digest.
289      */
290     public void update(byte input) {
291         engineUpdate(input);
292         state = IN_PROGRESS;
293     }
294 
295     /**
296      * Updates the digest using the specified array of bytes, starting
297      * at the specified offset.
298      *
299      * @param input the array of bytes.
300      *
301      * @param offset the offset to start from in the array of bytes.
302      *
303      * @param len the number of bytes to use, starting at
304      * <code>offset</code>.
305      */
306     public void update(byte[] input, int offset, int len) {
307         if (input == null) {
308             throw new IllegalArgumentException("No input buffer given");
309         }
310         if (input.length - offset < len) {
311             throw new IllegalArgumentException("Input buffer too short");
312         }
313         engineUpdate(input, offset, len);
314         state = IN_PROGRESS;
315     }
316 
317     /**
318      * Updates the digest using the specified array of bytes.
319      *
320      * @param input the array of bytes.
321      */
322     public void update(byte[] input) {
323         engineUpdate(input, 0, input.length);
324         state = IN_PROGRESS;
325     }
326 
327     /**
328      * Update the digest using the specified ByteBuffer. The digest is
329      * updated using the <code>input.remaining()</code> bytes starting
330      * at <code>input.position()</code>.
331      * Upon return, the buffer‘s position will be equal to its limit;
332      * its limit will not have changed.
333      *
334      * @param input the ByteBuffer
335      * @since 1.5
336      */
337     public final void update(ByteBuffer input) {
338         if (input == null) {
339             throw new NullPointerException();
340         }
341         engineUpdate(input);
342         state = IN_PROGRESS;
343     }
344 
345     /**
346      * Completes the hash computation by performing final operations
347      * such as padding. The digest is reset after this call is made.
348      *
349      * @return the array of bytes for the resulting hash value.
350      */
351     public byte[] digest() {
352         /* Resetting is the responsibility of implementors. */
353         byte[] result = engineDigest();
354         state = INITIAL;
355         return result;
356     }
357 
358     /**
359      * Completes the hash computation by performing final operations
360      * such as padding. The digest is reset after this call is made.
361      *
362      * @param buf output buffer for the computed digest
363      *
364      * @param offset offset into the output buffer to begin storing the digest
365      *
366      * @param len number of bytes within buf allotted for the digest
367      *
368      * @return the number of bytes placed into <code>buf</code>
369      *
370      * @exception DigestException if an error occurs.
371      */
372     public int digest(byte[] buf, int offset, int len) throws DigestException {
373         if (buf == null) {
374             throw new IllegalArgumentException("No output buffer given");
375         }
376         if (buf.length - offset < len) {
377             throw new IllegalArgumentException
378                 ("Output buffer too small for specified offset and length");
379         }
380         int numBytes = engineDigest(buf, offset, len);
381         state = INITIAL;
382         return numBytes;
383     }
384 
385     /**
386      * Performs a final update on the digest using the specified array
387      * of bytes, then completes the digest computation. That is, this
388      * method first calls {@link #update(byte[]) update(input)},
389      * passing the <i>input</i> array to the <code>update</code> method,
390      * then calls {@link #digest() digest()}.
391      *
392      * @param input the input to be updated before the digest is
393      * completed.
394      *
395      * @return the array of bytes for the resulting hash value.
396      */
397     public byte[] digest(byte[] input) {
398         update(input);
399         return digest();
400     }
401 
402     /**
403      * Returns a string representation of this message digest object.
404      */
405     public String toString() {
406         ByteArrayOutputStream baos = new ByteArrayOutputStream();
407         PrintStream p = new PrintStream(baos);
408         p.print(algorithm+" Message Digest from "+provider.getName()+", ");
409         switch (state) {
410         case INITIAL:
411             p.print("<initialized>");
412             break;
413         case IN_PROGRESS:
414             p.print("<in progress>");
415             break;
416         }
417         p.println();
418         return (baos.toString());
419     }
420 
421     /**
422      * Compares two digests for equality. Does a simple byte compare.
423      *
424      * @param digesta one of the digests to compare.
425      *
426      * @param digestb the other digest to compare.
427      *
428      * @return true if the digests are equal, false otherwise.
429      */
430     public static boolean isEqual(byte[] digesta, byte[] digestb) {
431         if (digesta.length != digestb.length) {
432             return false;
433         }
434 
435         int result = 0;
436         // time-constant comparison
437         for (int i = 0; i < digesta.length; i++) {
438             result |= digesta[i] ^ digestb[i];
439         }
440         return result == 0;
441     }
442 
443     /**
444      * Resets the digest for further use.
445      */
446     public void reset() {
447         engineReset();
448         state = INITIAL;
449     }
450 
451     /**
452      * Returns a string that identifies the algorithm, independent of
453      * implementation details. The name should be a standard
454      * Java Security name (such as "SHA", "MD5", and so on).
455      * See the MessageDigest section in the <a href=
456      * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">
457      * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
458      * for information about standard algorithm names.
459      *
460      * @return the name of the algorithm
461      */
462     public final String getAlgorithm() {
463         return this.algorithm;
464     }
465 
466     /**
467      * Returns the length of the digest in bytes, or 0 if this operation is
468      * not supported by the provider and the implementation is not cloneable.
469      *
470      * @return the digest length in bytes, or 0 if this operation is not
471      * supported by the provider and the implementation is not cloneable.
472      *
473      * @since 1.2
474      */
475     public final int getDigestLength() {
476         int digestLen = engineGetDigestLength();
477         if (digestLen == 0) {
478             try {
479                 MessageDigest md = (MessageDigest)clone();
480                 byte[] digest = md.digest();
481                 return digest.length;
482             } catch (CloneNotSupportedException e) {
483                 return digestLen;
484             }
485         }
486         return digestLen;
487     }
488 
489     /**
490      * Returns a clone if the implementation is cloneable.
491      *
492      * @return a clone if the implementation is cloneable.
493      *
494      * @exception CloneNotSupportedException if this is called on an
495      * implementation that does not support <code>Cloneable</code>.
496      */
497     public Object clone() throws CloneNotSupportedException {
498         if (this instanceof Cloneable) {
499             return super.clone();
500         } else {
501             throw new CloneNotSupportedException();
502         }
503     }
504 
505 
506 
507 
508     /*
509      * The following class allows providers to extend from MessageDigestSpi
510      * rather than from MessageDigest. It represents a MessageDigest with an
511      * encapsulated, provider-supplied SPI object (of type MessageDigestSpi).
512      * If the provider implementation is an instance of MessageDigestSpi,
513      * the getInstance() methods above return an instance of this class, with
514      * the SPI object encapsulated.
515      *
516      * Note: All SPI methods from the original MessageDigest class have been
517      * moved up the hierarchy into a new class (MessageDigestSpi), which has
518      * been interposed in the hierarchy between the API (MessageDigest)
519      * and its original parent (Object).
520      */
521 
522     static class Delegate extends MessageDigest {
523 
524         // The provider implementation (delegate)
525         private MessageDigestSpi digestSpi;
526 
527         // constructor
528         public Delegate(MessageDigestSpi digestSpi, String algorithm) {
529             super(algorithm);
530             this.digestSpi = digestSpi;
531         }
532 
533         /**
534          * Returns a clone if the delegate is cloneable.
535          *
536          * @return a clone if the delegate is cloneable.
537          *
538          * @exception CloneNotSupportedException if this is called on a
539          * delegate that does not support <code>Cloneable</code>.
540          */
541         public Object clone() throws CloneNotSupportedException {
542             if (digestSpi instanceof Cloneable) {
543                 MessageDigestSpi digestSpiClone =
544                     (MessageDigestSpi)digestSpi.clone();
545                 // Because ‘algorithm‘, ‘provider‘, and ‘state‘ are private
546                 // members of our supertype, we must perform a cast to
547                 // access them.
548                 MessageDigest that =
549                     new Delegate(digestSpiClone,
550                                  ((MessageDigest)this).algorithm);
551                 that.provider = ((MessageDigest)this).provider;
552                 that.state = ((MessageDigest)this).state;
553                 return that;
554             } else {
555                 throw new CloneNotSupportedException();
556             }
557         }
558 
559         protected int engineGetDigestLength() {
560             return digestSpi.engineGetDigestLength();
561         }
562 
563         protected void engineUpdate(byte input) {
564             digestSpi.engineUpdate(input);
565         }
566 
567         protected void engineUpdate(byte[] input, int offset, int len) {
568             digestSpi.engineUpdate(input, offset, len);
569         }
570 
571         protected void engineUpdate(ByteBuffer input) {
572             digestSpi.engineUpdate(input);
573         }
574 
575         protected byte[] engineDigest() {
576             return digestSpi.engineDigest();
577         }
578 
579         protected int engineDigest(byte[] buf, int offset, int len)
580             throws DigestException {
581                 return digestSpi.engineDigest(buf, offset, len);
582         }
583 
584         protected void engineReset() {
585             digestSpi.engineReset();
586         }
587     }
588 }