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25 
26 package java.security;
27 
28 import java.nio.ByteBuffer;
29 
30 import sun.security.jca.JCAUtil;
31 
32 /**
33  * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>)
34  * for the {@code MessageDigest} class, which provides the functionality
35  * of a message digest algorithm, such as MD5 or SHA. Message digests are
36  * secure one-way hash functions that take arbitrary-sized data and output a
37  * fixed-length hash value.
38  *
39  * <p> All the abstract methods in this class must be implemented by a
40  * cryptographic service provider who wishes to supply the implementation
41  * of a particular message digest algorithm.
42  *
43  * <p> Implementations are free to implement the Cloneable interface.
44  *
45  * @author Benjamin Renaud
46  *
47  *
48  * @see MessageDigest
49  */
50 
51 public abstract class MessageDigestSpi {
52 
53     // for re-use in engineUpdate(ByteBuffer input)
54     private byte[] tempArray;
55 
56     /**
57      * Returns the digest length in bytes.
58      *
59      * <p>This concrete method has been added to this previously-defined
60      * abstract class. (For backwards compatibility, it cannot be abstract.)
61      *
62      * <p>The default behavior is to return 0.
63      *
64      * <p>This method may be overridden by a provider to return the digest
65      * length.
66      *
67      * @return the digest length in bytes.
68      *
69      * @since 1.2
70      */
engineGetDigestLength()71     protected int engineGetDigestLength() {
72         return 0;
73     }
74 
75     /**
76      * Updates the digest using the specified byte.
77      *
78      * @param input the byte to use for the update.
79      */
engineUpdate(byte input)80     protected abstract void engineUpdate(byte input);
81 
82     /**
83      * Updates the digest using the specified array of bytes,
84      * starting at the specified offset.
85      *
86      * @param input the array of bytes to use for the update.
87      *
88      * @param offset the offset to start from in the array of bytes.
89      *
90      * @param len the number of bytes to use, starting at
91      * {@code offset}.
92      */
engineUpdate(byte[] input, int offset, int len)93     protected abstract void engineUpdate(byte[] input, int offset, int len);
94 
95     /**
96      * Update the digest using the specified ByteBuffer. The digest is
97      * updated using the {@code input.remaining()} bytes starting
98      * at {@code input.position()}.
99      * Upon return, the buffer's position will be equal to its limit;
100      * its limit will not have changed.
101      *
102      * @param input the ByteBuffer
103      * @since 1.5
104      */
engineUpdate(ByteBuffer input)105     protected void engineUpdate(ByteBuffer input) {
106         if (input.hasRemaining() == false) {
107             return;
108         }
109         if (input.hasArray()) {
110             byte[] b = input.array();
111             int ofs = input.arrayOffset();
112             int pos = input.position();
113             int lim = input.limit();
114             engineUpdate(b, ofs + pos, lim - pos);
115             input.position(lim);
116         } else {
117             int len = input.remaining();
118             int n = JCAUtil.getTempArraySize(len);
119             if ((tempArray == null) || (n > tempArray.length)) {
120                 tempArray = new byte[n];
121             }
122             while (len > 0) {
123                 int chunk = Math.min(len, tempArray.length);
124                 input.get(tempArray, 0, chunk);
125                 engineUpdate(tempArray, 0, chunk);
126                 len -= chunk;
127             }
128         }
129     }
130 
131     /**
132      * Completes the hash computation by performing final
133      * operations such as padding. Once {@code engineDigest} has
134      * been called, the engine should be reset (see
135      * {@link #engineReset() engineReset}).
136      * Resetting is the responsibility of the
137      * engine implementor.
138      *
139      * @return the array of bytes for the resulting hash value.
140      */
engineDigest()141     protected abstract byte[] engineDigest();
142 
143     /**
144      * Completes the hash computation by performing final
145      * operations such as padding. Once {@code engineDigest} has
146      * been called, the engine should be reset (see
147      * {@link #engineReset() engineReset}).
148      * Resetting is the responsibility of the
149      * engine implementor.
150      *
151      * This method should be abstract, but we leave it concrete for
152      * binary compatibility.  Knowledgeable providers should override this
153      * method.
154      *
155      * @param buf the output buffer in which to store the digest
156      *
157      * @param offset offset to start from in the output buffer
158      *
159      * @param len number of bytes within buf allotted for the digest.
160      * Both this default implementation and the SUN provider do not
161      * return partial digests.  The presence of this parameter is solely
162      * for consistency in our API's.  If the value of this parameter is less
163      * than the actual digest length, the method will throw a DigestException.
164      * This parameter is ignored if its value is greater than or equal to
165      * the actual digest length.
166      *
167      * @return the length of the digest stored in the output buffer.
168      *
169      * @exception DigestException if an error occurs.
170      *
171      * @since 1.2
172      */
engineDigest(byte[] buf, int offset, int len)173     protected int engineDigest(byte[] buf, int offset, int len)
174                                                 throws DigestException {
175 
176         byte[] digest = engineDigest();
177         if (len < digest.length)
178                 throw new DigestException("partial digests not returned");
179         if (buf.length - offset < digest.length)
180                 throw new DigestException("insufficient space in the output "
181                                           + "buffer to store the digest");
182         System.arraycopy(digest, 0, buf, offset, digest.length);
183         return digest.length;
184     }
185 
186     /**
187      * Resets the digest for further use.
188      */
engineReset()189     protected abstract void engineReset();
190 
191     /**
192      * Returns a clone if the implementation is cloneable.
193      *
194      * @return a clone if the implementation is cloneable.
195      *
196      * @exception CloneNotSupportedException if this is called on an
197      * implementation that does not support {@code Cloneable}.
198      */
clone()199     public Object clone() throws CloneNotSupportedException {
200         if (this instanceof Cloneable) {
201             return super.clone();
202         } else {
203             throw new CloneNotSupportedException();
204         }
205     }
206 }
207