MessageDigest JDK 1.6)

Description

publicabstract abstract class MessageDigest

This MessageDigest class provides applications the functionality of a message digest algorithm, such as MD5 or SHA.

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 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.

See also: DigestInputStream DigestOutputStream

Methods

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public Object clone () throws CloneNotSupportedException [Overrides MessageDigestSpi]

Returns a clone if the implementation is cloneable.

Returns a clone if the implementation is cloneable.
Returns: a clone if the implementation is cloneable.
Throws:
- CloneNotSupportedException - if this is called on an implementation that does not support Cloneable.

public byte digest ()

Completes the hash computation by performing final operations such as padding.

public byte digest (byte[] input)

Performs a final update on the digest using the specified array of bytes, then completes the digest computation.

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().
Returns: the array of bytes for the resulting hash value.
Parameters:
- input - the input to be updated before the digest is completed.

public int digest (byte[] buf, int offset, int len) throws DigestException

Completes the hash computation by performing final operations such as padding.

Completes the hash computation by performing final operations
such as padding. The digest is reset after this call is made.
Returns: the number of bytes placed into buf
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
Throws:
- DigestException - if an error occurs.

protectedabstract byte engineDigest () [Inherited From MessageDigestSpi]

Completes the hash computation by performing final operations such as padding.

protected int engineDigest (byte[] buf, int offset, int len) throws DigestException [Inherited From MessageDigestSpi]

Completes the hash computation by performing final operations such as padding.

Completes the hash computation by performing final
operations such as padding. Once engineDigest has
been called, the engine should be reset (see
engineReset).
Resetting is the responsibility of the
engine implementor.

This method should be abstract, but we leave it concrete for
binary compatibility. Knowledgeable providers should override this
method.
Returns: the length of the digest stored in the output buffer.
Parameters:
- buf - the output buffer in which to store the digest
- offset - offset to start from in the output buffer
- len - number of bytes within buf allotted for the digest. Both this default implementation and the SUN provider do not return partial digests. The presence of this parameter is solely for consistency in our API's. If the value of this parameter is less than the actual digest length, the method will throw a DigestException. This parameter is ignored if its value is greater than or equal to the actual digest length.
Throws:
- DigestException - if an error occurs.
Since: 1.2

protected int engineGetDigestLength () [Inherited From MessageDigestSpi]

Returns the digest length in bytes.

protectedabstract void engineReset () [Inherited From MessageDigestSpi]

Resets the digest for further use.

protectedabstract void engineUpdate (byte input) [Inherited From MessageDigestSpi]

Updates the digest using the specified byte.

protectedabstract void engineUpdate (byte[] input, int offset, int len) [Inherited From MessageDigestSpi]

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

Updates the digest using the specified array of bytes,
starting at the specified offset.
Parameters:
- input - the array of bytes to use for the update.
- offset - the offset to start from in the array of bytes.
- len - the number of bytes to use, starting at offset.

protected void engineUpdate (ByteBuffer input) [Inherited From MessageDigestSpi]

Update the digest using the specified ByteBuffer.

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.
Parameters:
- input - the ByteBuffer
Since: 1.5

publicfinal String getAlgorithm ()

Returns a string that identifies the algorithm, independent of implementation details.

publicfinal 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.

publicstatic MessageDigest getInstance (String algorithm) throws NoSuchAlgorithmException

Returns a MessageDigest object that implements the specified digest algorithm.

publicstatic MessageDigest getInstance (String algorithm, Provider provider) throws NoSuchAlgorithmException

Returns a MessageDigest object that implements the specified digest algorithm.

publicstatic MessageDigest getInstance (String algorithm, String provider) throws NoSuchAlgorithmException NoSuchProviderException

Returns a MessageDigest object that implements the specified digest algorithm.

publicfinal Provider getProvider ()

Returns the provider of this message digest object.

publicstatic boolean isEqual (byte[] digesta, byte[] digestb)

Compares two digests for equality.

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

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

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.

publicfinal void update (ByteBuffer input)

Update the digest using the specified ByteBuffer.