java.security
Class MessageDigest

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

public abstract class MessageDigest

extends MessageDigestSpi

This class provides the functionality of a digest algorithm, like MD5 or SHA. This class is is abstract and extends from MessageDigestSpi to be compatible with JDK, which does it for historical reasons (check the JDK's Javadoc files).

Constructor Summary

protected

MessageDigest(String algorithmName) Create a new MessageDigest with its algorithm set to the argument.

Method Summary

Object	clone() Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
byte[]	digest() Computes and answers the final hash value that the receiver represents.
byte[]	digest(byte[] bytesToHash) Includes the bytes of the argument in the hash value computed by the receiver, and then computes the final digest value.
int	digest(byte[] buffer, int offset, int length) Computes the digest and stores it into the buffer passed as parameter.
String	getAlgorithm() Answers the standard Java Security name for the algorithm being used by the receiver.
int	getDigestLength() Return the engine digest length in bytes.
static MessageDigest	getInstance(String algorithmName) Answers a new MessageDigest which is capable of running the algorithm described by the argument.
static MessageDigest	getInstance(String algorithmName, Provider provider) Answers a new MessageDigest which is capable of running the algorithm described by the argument.
static MessageDigest	getInstance(String algorithmName, String providerName) Answers a new MessageDigest which is capable of running the algorithm described by the argument.
Provider	getProvider() Returns the Provider of the digest represented by the receiver.
static boolean	isEqual(byte[] digesta, byte[] digestb) Does a simply byte-per-byte compare of the two digests.
void	reset() Puts the receiver back in an initial state, such that it is ready to compute a new hash.
String	toString() Answers a string containing a concise, human-readable description of the receiver.
void	update(byte byteToHash) Includes the argument in the hash value computed by the receiver.
void	update(byte[] bytesToHash) Includes the bytes of the argument in the hash value computed by the receiver.
void	update(byte[] bytesToHash, int offset, int count) Includes a range of bytes from the first argument in the hash value computed by the receiver.

Methods inherited from class java.security.MessageDigestSpi

engineDigest, engineDigest, engineGetDigestLength, engineReset, engineUpdate, engineUpdate

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

MessageDigest

protected MessageDigest(String algorithmName)

Create a new MessageDigest with its algorithm set to the argument.

Parameters:

algorithmName - java.lang.String the algorithm that the receiver will represent

Method Detail

clone

public Object clone()
             throws CloneNotSupportedException

Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.

Classes which wish to support cloning must specify that they implement the Cloneable interface, since the native implementation checks for this.

Overrides:

clone in class MessageDigestSpi

Returns:

a shallow copy of this object

Throws:

CloneNotSupportedException - if the component does not implement the interface Cloneable

digest

public byte[] digest()

Computes and answers the final hash value that the receiver represents. After the digest is computed the receiver is reset.

Returns:

the hash the receiver computed

See Also:

reset()

digest

public byte[] digest(byte[] bytesToHash)

Includes the bytes of the argument in the hash value computed by the receiver, and then computes the final digest value.

Parameters:

bytesToHash - byte[] the source array

Returns:

the hash the receiver computed

See Also:

update(byte), update(byte[]), update(byte[], int, int), digest(), digest(byte[]), digest(byte[], int, int)

digest

public int digest(byte[] buffer,
                  int offset,
                  int length)
           throws DigestException

Computes the digest and stores it into the buffer passed as parameter.

Parameters:

buffer - byte[] the array into which to store the digest

offset - the starting offset into the array

length - the number of bytes available to store the digest

Returns:

the number of bytes copied

Throws:

DigestException - If an error occurs

See Also:

digest(), digest(byte[]), digest(byte[], int, int)

getAlgorithm

public final String getAlgorithm()

Answers the standard Java Security name for the algorithm being used by the receiver.

Returns:

String the name of the algorithm

getDigestLength

public final int getDigestLength()

Return the engine digest length in bytes. Default is 0.

Returns:

int the engine digest length in bytes

getInstance

public static MessageDigest getInstance(String algorithmName)
                                 throws NoSuchAlgorithmException

Answers a new MessageDigest which is capable of running the algorithm described by the argument. The result will be an instance of a subclass of MessageDigest which implements that algorithm.

Parameters:

algorithmName - java.lang.String Name of the algorithm desired

Returns:

MessageDigest a concrete implementation for the algorithm desired.

Throws:

NoSuchAlgorithmException - If the algorithm cannot be found

getInstance

public static MessageDigest getInstance(String algorithmName,
                                        String providerName)
                                 throws NoSuchAlgorithmException,
                                        NoSuchProviderException

Answers a new MessageDigest which is capable of running the algorithm described by the argument. The result will be an instance of a subclass of MessageDigest which implements that algorithm.

Parameters:

algorithmName - java.lang.String Name of the algorithm desired

providerName - java.lang.String Name of the provider which has to implement the algorithm

Returns:

MessageDigest a concrete implementation for the algorithm desired.

Throws:

NoSuchAlgorithmException - If the algorithm cannot be found

NoSuchProviderException - If the provider cannot be found

getInstance

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

Answers a new MessageDigest which is capable of running the algorithm described by the argument. The result will be an instance of a subclass of MessageDigest which implements that algorithm.

Parameters:

provider - Provider Provider which has to implement the algorithm

Returns:

MessageDigest a concrete implementation for the algorithm desired.

Throws:

NoSuchAlgorithmException - If the algorithm cannot be found

getProvider

public final Provider getProvider()

Returns the Provider of the digest represented by the receiver.

Returns:

Provider an instance of a subclass of java.security.Provider

isEqual

public static boolean isEqual(byte[] digesta,
                              byte[] digestb)

Does a simply byte-per-byte compare of the two digests.

Parameters:

digesta - One of the digests to compare

digestb - The digest to compare to

Returns:

true if the two hashes are equal false if the two hashes are not equal

reset

public void reset()

Puts the receiver back in an initial state, such that it is ready to compute a new hash.

See Also:

MessageDigest.Wrapper.engineReset()

toString

public String toString()

Answers a string containing a concise, human-readable description of the receiver.

Overrides:

toString in class Object

Returns:

a printable representation for the receiver.

update

public void update(byte[] bytesToHash)

Includes the bytes of the argument in the hash value computed by the receiver.

Parameters:

bytesToHash - byte[] the source array

update

public void update(byte[] bytesToHash,
                   int offset,
                   int count)

Includes a range of bytes from the first argument in the hash value computed by the receiver.

Parameters:

bytesToHash - byte[] the source array

offset - the starting offset into the array

count - the number of bytes to include in the hash

update

public void update(byte byteToHash)

Includes the argument in the hash value computed by the receiver.

Parameters:

byteToHash - byte the byte to feed to the hash algorithm

See Also:

reset()