MessageDigest

public abstract class MessageDigest extends MessageDigestSpi

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.

Android provides the following MessageDigest algorithms:

Algorithm	Supported API Levels
MD5	1+
SHA-1	1+
SHA-224	1-8,22+
SHA-256	1+
SHA-384	1+
SHA-512	1+

These algorithms are described in the MessageDigest section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

See Also

• DigestInputStream
• DigestOutputStream

Protected Constructor Summary

MessageDigest(String algorithm) Creates a message digest with the specified algorithm name.

Public Method Summary

Object	clone() Returns a clone if the implementation is cloneable.
int	digest(byte[] buf, int offset, int len) Completes the hash computation by performing final operations such as padding.
byte[]	digest() Completes the hash computation by performing final operations such as padding.
byte[]	digest(byte[] input) Performs a final update on the digest using the specified array of bytes, then completes the digest computation.
final String	getAlgorithm() Returns a string that identifies the algorithm, independent of implementation details.
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.
static MessageDigest	getInstance(String algorithm) Returns a MessageDigest object that implements the specified digest algorithm.
static MessageDigest	getInstance(String algorithm, String provider) Returns a MessageDigest object that implements the specified digest algorithm.
static MessageDigest	getInstance(String algorithm, Provider provider) Returns a MessageDigest object that implements the specified digest algorithm.
final Provider	getProvider() Returns the provider of this message digest object.
static boolean	isEqual(byte[] digesta, byte[] digestb) Compares two digests for equality.
void	reset() Resets the digest for further use.
String	toString() Returns a string representation of this message digest object.
void	update(byte[] input) Updates the digest using the specified array of bytes.
void	update(byte[] input, int offset, int len) Updates the digest using the specified array of bytes, starting at the specified offset.
final void	update(ByteBuffer input) Update the digest using the specified ByteBuffer.
void	update(byte input) Updates the digest using the specified byte.

Inherited Method Summary

From class java.security.MessageDigestSpi

Object	clone() Returns a clone if the implementation is cloneable.
int	engineDigest(byte[] buf, int offset, int len) Completes the hash computation by performing final operations such as padding.
abstract byte[]	engineDigest() Completes the hash computation by performing final operations such as padding.
int	engineGetDigestLength() Returns the digest length in bytes.
abstract void	engineReset() Resets the digest for further use.
void	engineUpdate(ByteBuffer input) Update the digest using the specified ByteBuffer.
abstract void	engineUpdate(byte input) Updates the digest using the specified byte.
abstract void	engineUpdate(byte[] input, int offset, int len) Updates the digest using the specified array of bytes, starting at the specified offset.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Protected Constructors

protected MessageDigest (String algorithm)

Creates a message digest with the specified algorithm name.

Parameters

algorithm	the standard name of the digest algorithm. See the MessageDigest section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.

Public Methods

public Object clone ()

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 int digest (byte[] buf, int offset, int len)

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.

public byte[] digest ()

Completes the hash computation by performing final operations such as padding. The digest is reset after this call is made.

Returns

• the array of bytes for the resulting hash value.

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().

Parameters

input	the input to be updated before the digest is completed.

Returns

• the array of bytes for the resulting hash value.

public final String getAlgorithm ()

Returns a string that identifies the algorithm, independent of implementation details. The name should be a standard Java Security name (such as "SHA", "MD5", and so on). See the MessageDigest section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.

Returns

• the name of the algorithm

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.

Returns

• the digest length 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)

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.

Parameters

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.

Returns

• a Message Digest object that implements the specified algorithm.

Throws

NoSuchAlgorithmException	if no Provider supports a MessageDigestSpi implementation for the specified algorithm.

See Also

• Provider

public static MessageDigest getInstance (String algorithm, String provider)

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.

Parameters

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.
provider	the name of the provider.

Returns

• a MessageDigest object that implements the specified algorithm.

Throws

NoSuchAlgorithmException	if a MessageDigestSpi implementation for the specified algorithm is not available from the specified provider.
NoSuchProviderException	if the specified provider is not registered in the security provider list.
IllegalArgumentException	if the provider name is null or empty.

See Also

• Provider

public static MessageDigest getInstance (String algorithm, Provider provider)

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.

Parameters

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.
provider	the provider.

Returns

• a MessageDigest object that implements the specified algorithm.

Throws

NoSuchAlgorithmException	if a MessageDigestSpi implementation for the specified algorithm is not available from the specified Provider object.
IllegalArgumentException	if the specified provider is null.

See Also

• Provider

public final Provider getProvider ()

Returns the provider of this message digest object.

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.

Parameters

digesta	one of the digests to compare.
digestb	the other digest to compare.

Returns

• true if the digests are equal, false otherwise.

public void reset ()

Resets the digest for further use.

public String toString ()

Returns a string representation of this message digest object.

Returns

• a printable representation of this object.

public void update (byte[] input)

Updates the digest using the specified array of bytes.

Parameters

input	the 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.

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.

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.

Parameters

input	the ByteBuffer

public void update (byte input)

Updates the digest using the specified byte.

Parameters

input	the byte with which to update the digest.