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java.security
abstract public class: MessageDigest [javadoc | source]
java.lang.Object
   java.security.MessageDigestSpi
      java.security.MessageDigest

Direct Known Subclasses:
    DummyMessageDigest, Delegate

This MessageDigest class provides applications the functionality of a message digest algorithm, such as SHA-1 or SHA-256. Message digests are secure one-way hash functions that take arbitrary-sized data and output a fixed-length hash value.

A MessageDigest object starts out initialized. The data is processed through it using the update methods. At any point reset can be called to reset the digest. Once all the data to be updated has been updated, one of the digest methods should be called to complete the hash computation.

The digest method can be called once for a given number of updates. After 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 MessageDigestSpi for historical reasons. Application developers should only take notice of the methods defined in this 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 MessageDigest algorithms:

These algorithms are described in the MessageDigest section of the Java Cryptography Architecture Standard Algorithm Name Documentation. Consult the release documentation for your implementation to see if any other algorithms are supported.
Nested Class Summary:
static class  MessageDigest.Delegate   
Constructor:
 protected MessageDigest(String algorithm) 
    Creates a message digest with the specified algorithm name.
Method from java.security.MessageDigest Summary:
clone,   digest,   digest,   digest,   getAlgorithm,   getDigestLength,   getInstance,   getInstance,   getInstance,   getProvider,   isEqual,   reset,   toString,   update,   update,   update,   update
Methods from java.security.MessageDigestSpi:
clone,   engineDigest,   engineDigest,   engineGetDigestLength,   engineReset,   engineUpdate,   engineUpdate,   engineUpdate
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.security.MessageDigest Detail:
 public Object clone() throws CloneNotSupportedException 
    Returns a clone if the implementation is cloneable.
 public byte[] digest() 
    Completes the hash computation by performing final operations such as padding. The digest is reset after this call is made.
 public byte[] digest(byte[] input) 
    Performs a final update on the digest using the specified array of bytes, then completes the digest computation. That is, this method first calls update(input) , passing the input array to the update method, then calls digest() .
 public int digest(byte[] buf,
    int offset,
    int len) throws DigestException 
    Completes the hash computation by performing final operations such as padding. The digest is reset after this call is made.
 public final String getAlgorithm() 
 public final int getDigestLength() 
    Returns the length of the digest in bytes, or 0 if this operation is not supported by the provider and the implementation is not cloneable.
 public static MessageDigest getInstance(String algorithm) throws NoSuchAlgorithmException 
    Returns a MessageDigest object that implements the specified digest algorithm.

    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 Security.getProviders() method.

 public static MessageDigest getInstance(String algorithm,
    String provider) throws NoSuchAlgorithmException, NoSuchProviderException 
    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 Security.getProviders() method.

 public static MessageDigest getInstance(String algorithm,
    Provider provider) throws NoSuchAlgorithmException 
    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.

 public final Provider getProvider() 
    Returns the provider of this message digest object.
 public static boolean isEqual(byte[] digesta,
    byte[] digestb) 
    Compares two digests for equality. Does a simple byte compare.
 public  void reset() 
    Resets the digest for further use.
 public String toString() 
    Returns a string representation of this message digest object.
 public  void update(byte input) 
    Updates the digest using the specified byte.
 public  void update(byte[] input) 
    Updates the digest using the specified array of bytes.
 public final  void update(ByteBuffer input) 
    Update the digest using the specified ByteBuffer. The digest is updated using the input.remaining() bytes starting at input.position(). Upon return, the buffer's position will be equal to its limit; its limit will not have changed.
 public  void update(byte[] input,
    int offset,
    int len) 
    Updates the digest using the specified array of bytes, starting at the specified offset.