A MessageDigest object starts out initialized. The data is * processed through it using the {@link #update(byte) update} * methods. At any point {@link #reset() reset} can be called * to reset the digest. Once all the data to be updated has been * updated, one of the {@link #digest() digest} methods should * be called to complete the hash computation. * *
The {@code digest} method can be called once for a given number * of updates. After {@code digest} has been called, the MessageDigest * object is reset to its initialized state. * *
Implementations are free to implement the Cloneable interface. * Client applications can test cloneability by attempting cloning * and catching the CloneNotSupportedException:
* *
* MessageDigest md = MessageDigest.getInstance("SHA");
*
* try {
* md.update(toChapter1);
* MessageDigest tc1 = md.clone();
* byte[] toChapter1Digest = tc1.digest();
* md.update(toChapter2);
* ...etc.
* } catch (CloneNotSupportedException cnse) {
* throw new DigestException("couldn't make digest of partial content");
* }
*
*
* Note that if a given implementation is not cloneable, it is * still possible to compute intermediate digests by instantiating * several instances, if the number of digests is known in advance. * *
Note that this class is abstract and extends from * {@code MessageDigestSpi} for historical reasons. * Application developers should only take notice of the methods defined in * this {@code MessageDigest} class; all the methods in * the superclass are intended for cryptographic service providers who wish to * supply their own implementations of message digest algorithms. * *
Every implementation of the Java platform is required to support * the following standard {@code MessageDigest} algorithms: *
This method traverses the list of registered security Providers, * starting with the most preferred Provider. * A new MessageDigest object encapsulating the * MessageDigestSpi implementation from the first * Provider that supports the specified algorithm is returned. * *
Note that the list of registered providers may be retrieved via * the {@link Security#getProviders() Security.getProviders()} method. * * @param algorithm the name of the algorithm requested. * See the MessageDigest section in the * Java Cryptography Architecture Standard Algorithm Name Documentation * for information about standard algorithm names. * * @return a Message Digest object that implements the specified algorithm. * * @exception NoSuchAlgorithmException if no Provider supports a * MessageDigestSpi implementation for the * specified algorithm. * * @see Provider */ public static MessageDigest getInstance(String algorithm) throws NoSuchAlgorithmException { try { Object[] objs = Security.getImpl(algorithm, "MessageDigest", (String)null); if (objs[0] instanceof MessageDigest) { MessageDigest md = (MessageDigest)objs[0]; md.provider = (Provider)objs[1]; return md; } else { MessageDigest delegate = new Delegate((MessageDigestSpi)objs[0], algorithm); delegate.provider = (Provider)objs[1]; return delegate; } } catch(NoSuchProviderException e) { throw new NoSuchAlgorithmException(algorithm + " not found"); } } /** * Returns a MessageDigest object that implements the specified digest * algorithm. * *
A new MessageDigest object encapsulating the * MessageDigestSpi implementation from the specified provider * is returned. The specified provider must be registered * in the security provider list. * *
Note that the list of registered providers may be retrieved via * the {@link Security#getProviders() Security.getProviders()} method. * * @param algorithm the name of the algorithm requested. * See the MessageDigest section in the * Java Cryptography Architecture Standard Algorithm Name Documentation * for information about standard algorithm names. * * @param provider the name of the provider. * * @return a MessageDigest object that implements the specified algorithm. * * @exception NoSuchAlgorithmException if a MessageDigestSpi * implementation for the specified algorithm is not * available from the specified provider. * * @exception NoSuchProviderException if the specified provider is not * registered in the security provider list. * * @exception IllegalArgumentException if the provider name is null * or empty. * * @see Provider */ public static MessageDigest getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException { if (provider == null || provider.length() == 0) throw new IllegalArgumentException("missing provider"); Object[] objs = Security.getImpl(algorithm, "MessageDigest", provider); if (objs[0] instanceof MessageDigest) { MessageDigest md = (MessageDigest)objs[0]; md.provider = (Provider)objs[1]; return md; } else { MessageDigest delegate = new Delegate((MessageDigestSpi)objs[0], algorithm); delegate.provider = (Provider)objs[1]; return delegate; } } /** * Returns a MessageDigest object that implements the specified digest * algorithm. * *
A new MessageDigest object encapsulating the
* MessageDigestSpi implementation from the specified Provider
* object is returned. Note that the specified Provider object
* does not have to be registered in the provider list.
*
* @param algorithm the name of the algorithm requested.
* See the MessageDigest section in the
* Java Cryptography Architecture Standard Algorithm Name Documentation
* for information about standard algorithm names.
*
* @param provider the provider.
*
* @return a MessageDigest object that implements the specified algorithm.
*
* @exception NoSuchAlgorithmException if a MessageDigestSpi
* implementation for the specified algorithm is not available
* from the specified Provider object.
*
* @exception IllegalArgumentException if the specified provider is null.
*
* @see Provider
*
* @since 1.4
*/
public static MessageDigest getInstance(String algorithm,
Provider provider)
throws NoSuchAlgorithmException
{
if (provider == null)
throw new IllegalArgumentException("missing provider");
Object[] objs = Security.getImpl(algorithm, "MessageDigest", provider);
if (objs[0] instanceof MessageDigest) {
MessageDigest md = (MessageDigest)objs[0];
md.provider = (Provider)objs[1];
return md;
} else {
MessageDigest delegate =
new Delegate((MessageDigestSpi)objs[0], algorithm);
delegate.provider = (Provider)objs[1];
return delegate;
}
}
/**
* Returns the provider of this message digest object.
*
* @return the provider of this message digest object
*/
public final Provider getProvider() {
return this.provider;
}
/**
* Updates the digest using the specified byte.
*
* @param input the byte with which to update the digest.
*/
public void update(byte input) {
engineUpdate(input);
state = IN_PROGRESS;
}
/**
* Updates the digest using the specified array of bytes, starting
* at the specified offset.
*
* @param input the array of bytes.
*
* @param offset the offset to start from in the array of bytes.
*
* @param len the number of bytes to use, starting at
* {@code offset}.
*/
public void update(byte[] input, int offset, int len) {
if (input == null) {
throw new IllegalArgumentException("No input buffer given");
}
if (input.length - offset < len) {
throw new IllegalArgumentException("Input buffer too short");
}
engineUpdate(input, offset, len);
state = IN_PROGRESS;
}
/**
* Updates the digest using the specified array of bytes.
*
* @param input the array of bytes.
*/
public void update(byte[] input) {
engineUpdate(input, 0, input.length);
state = IN_PROGRESS;
}
/**
* Update the digest using the specified ByteBuffer. The digest is
* updated using the {@code input.remaining()} bytes starting
* at {@code input.position()}.
* Upon return, the buffer's position will be equal to its limit;
* its limit will not have changed.
*
* @param input the ByteBuffer
* @since 1.5
*/
public final void update(ByteBuffer input) {
if (input == null) {
throw new NullPointerException();
}
engineUpdate(input);
state = IN_PROGRESS;
}
/**
* Completes the hash computation by performing final operations
* such as padding. The digest is reset after this call is made.
*
* @return the array of bytes for the resulting hash value.
*/
public byte[] digest() {
/* Resetting is the responsibility of implementors. */
byte[] result = engineDigest();
state = INITIAL;
return result;
}
/**
* Completes the hash computation by performing final operations
* such as padding. The digest is reset after this call is made.
*
* @param buf output buffer for the computed digest
*
* @param offset offset into the output buffer to begin storing the digest
*
* @param len number of bytes within buf allotted for the digest
*
* @return the number of bytes placed into {@code buf}
*
* @exception DigestException if an error occurs.
*/
public int digest(byte[] buf, int offset, int len) throws DigestException {
if (buf == null) {
throw new IllegalArgumentException("No output buffer given");
}
if (buf.length - offset < len) {
throw new IllegalArgumentException
("Output buffer too small for specified offset and length");
}
int numBytes = engineDigest(buf, offset, len);
state = INITIAL;
return numBytes;
}
/**
* Performs a final update on the digest using the specified array
* of bytes, then completes the digest computation. That is, this
* method first calls {@link #update(byte[]) update(input)},
* passing the input array to the {@code update} method,
* then calls {@link #digest() digest()}.
*
* @param input the input to be updated before the digest is
* completed.
*
* @return the array of bytes for the resulting hash value.
*/
public byte[] digest(byte[] input) {
update(input);
return digest();
}
/**
* Returns a string representation of this message digest object.
*/
public String toString() {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream p = new PrintStream(baos);
p.print(algorithm+" Message Digest from "+provider.getName()+", ");
switch (state) {
case INITIAL:
p.print("