Added in API level 1

Summary: Protected Ctors | Methods | Inherited Methods

MessageDigest

public abstract class MessageDigest
extends MessageDigestSpi

java.lang.Object
↳	java.security.MessageDigestSpi
	↳	java.security.MessageDigest

---

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-256");

 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

Summary

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

Public methods
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 methods
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) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Protected constructors

MessageDigest

Added in API level 1

protected MessageDigest (String algorithm)

Creates a message digest with the specified algorithm name.

Parameters
algorithm	String: the standard name of the digest algorithm. See the MessageDigest section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.

Public methods

clone

Added in API level 1

public Object clone ()

Returns a clone if the implementation is cloneable.

Returns
Object	a clone if the implementation is cloneable.

Throws
CloneNotSupportedException	if this is called on an implementation that does not support Cloneable.

digest

Added in API level 1

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	byte: output buffer for the computed digest
offset	int: offset into the output buffer to begin storing the digest
len	int: number of bytes within buf allotted for the digest

Returns
int	the number of bytes placed into buf

Throws
DigestException	if an error occurs.

digest

Added in API level 1

public byte[] digest ()

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

Returns
byte[]	the array of bytes for the resulting hash value.

digest

Added in API level 1

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

Returns
byte[]	the array of bytes for the resulting hash value.

getAlgorithm

Added in API level 1

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-256"). See the MessageDigest section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.

Returns
String	the name of the algorithm

getDigestLength

Added in API level 1

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
int	the digest length in bytes, or 0 if this operation is not supported by the provider and the implementation is not cloneable.

getInstance

Added in API level 1

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.

Implementation Note:

• The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().

Parameters
algorithm	String: the name of the algorithm requested. See the MessageDigest section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.

Returns
MessageDigest	a MessageDigest object that implements the specified algorithm

Throws
NoSuchAlgorithmException	if no Provider supports a MessageDigestSpi implementation for the specified algorithm
NullPointerException	if algorithm is null

See also:

• Provider

getInstance

Added in API level 1

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	String: the name of the algorithm requested. See the MessageDigest section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
provider	String: the name of the provider.

Returns
MessageDigest	a MessageDigest object that implements the specified algorithm

Throws
IllegalArgumentException	if the provider name is null or empty
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
NullPointerException	if algorithm is null

See also:

• Provider

getInstance

Added in API level 1

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	String: the name of the algorithm requested. See the MessageDigest section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
provider	Provider: the provider.

Returns
MessageDigest	a MessageDigest object that implements the specified algorithm

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

See also:

• Provider

getProvider

Added in API level 1

public final Provider getProvider ()

Returns the provider of this message digest object.

Returns
Provider	the provider of this message digest object

isEqual

Added in API level 1

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

Compares two digests for equality. Two digests are equal if they have the same length and all bytes at corresponding positions are equal.

Implementation Note:

• All bytes in digesta are examined to determine equality. The calculation time depends only on the length of digesta. It does not depend on the length of digestb or the contents of digesta and digestb.

Parameters
digesta	byte: one of the digests to compare.
digestb	byte: the other digest to compare.

Returns
boolean	true if the digests are equal, false otherwise.

reset

Added in API level 1

public void reset ()

Resets the digest for further use.

toString

Added in API level 1

public String toString ()

Returns a string representation of this message digest object.

Returns
String	a string representation of the object.

update

Added in API level 1

public void update (byte[] input)

Updates the digest using the specified array of bytes.

Parameters
input	byte: the array of bytes.

update

Added in API level 1

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	byte: the array of bytes.
offset	int: the offset to start from in the array of bytes.
len	int: the number of bytes to use, starting at offset.

update

Added in API level 1

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	ByteBuffer: the ByteBuffer

update

Added in API level 1

public void update (byte input)

Updates the digest using the specified byte.

Parameters
input	byte: the byte with which to update the digest.