java.security
Class MessageDigest

java.lang.Object
  |
  +--java.security.MessageDigest

public abstract class MessageDigest

extends Object

This MessageDigest class provides applications the functionality of a message digest algorithm, such as MD5 or SHA. 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 method. At any point reset can be called to reset the digest. Once all the data to be updated has been updated, the digest method 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.

Method Summary

int	digest(byte[] buf, int offset, int len) Completes the hash computation by performing final operations such as padding.
static MessageDigest	getInstance(String algorithm) Generates a MessageDigest object that implements the specified digest algorithm.
void	reset() Resets the digest for further use.
void	update(byte[] input, int offset, int len) Updates the digest using the specified array of bytes, starting at the specified offset.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

getInstance

public static MessageDigest getInstance(String algorithm)
                                 throws NoSuchAlgorithmException

Generates a MessageDigest object that implements the specified digest algorithm.

Parameters:

algorithm - the name of the algorithm requested. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

Returns:

a MessageDigest object implementing the specified algorithm.

Throws:

NoSuchAlgorithmException - if the algorithm is not available in the caller's environment.

update

public void update(byte[] input,
                   int offset,
                   int len)

Updates the digest using the specified array of bytes, starting at the specified offset.

Parameters:

input - the array of bytes.

offset - the offset to start from in the array of bytes.

len - the number of bytes to use, starting at offset.

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.

Parameters:

buf - output buffer for the computed digest

offset - offset into the output buffer to begin storing the digest

len - number of bytes within buf allotted for the digest

Returns:

the number of bytes placed into buf

Throws:

DigestException - if an error occurs.

reset

public void reset()

Resets the digest for further use.