java.lang.Object
- java.security.MessageDigestSpi
- - java.security.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.
Every implementation of the Java platform is required to support the following standard MessageDigest algorithms:
- MD5
- SHA-1
- SHA-256
These algorithms are described in the MessageDigest section of the Java Cryptography Architecture Standard Algorithm Name Documentation. Consult the release documentation for your implementation to see if any other algorithms are supported.

Constructor Summary

Constructors
Modifier Constructor Description

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

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`java.lang.Object`	`clone()`	Returns a clone if the implementation is cloneable.
`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.
`int`	`digest(byte[] buf, int offset, int len)`	Completes the hash computation by performing final operations such as padding.
`java.lang.String`	`getAlgorithm()`	Returns a string that identifies the algorithm, independent of implementation details.
`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(java.lang.String algorithm)`	Returns a MessageDigest object that implements the specified digest algorithm.
`static MessageDigest`	`getInstance(java.lang.String algorithm, java.lang.String provider)`	Returns a MessageDigest object that implements the specified digest algorithm.
`static boolean`	`isEqual(byte[] digesta, byte[] digestb)`	Compares two digests for equality.
`void`	`reset()`	Resets the digest for further use.
`java.lang.String`	`toString()`	Returns a string representation of this message digest object.
`void`	`update(byte input)`	Updates the digest using the specified byte.
`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.

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(java.lang.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 Security Standard Algorithm Names Specification for information about standard algorithm names. Consult the release documentation for your implementation to see which algorithms are supported.
- Method Detail
  - getInstance
```
public static MessageDigest getInstance(java.lang.String algorithm)
                                 throws NoSuchAlgorithmException
```
    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.
    
    Parameters:
    
    algorithm - the name of the algorithm requested. See the MessageDigest Algorithms section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names. Consult the release documentation for your implementation to see which types are supported.
    
    Returns:
    
    a Message Digest object that implements the specified algorithm.
    
    Throws:
    
    NoSuchAlgorithmException - if no Provider supports a MessageDigestSpi implementation for the specified algorithm.
  - getInstance
```
public static MessageDigest getInstance(java.lang.String algorithm,
                                        java.lang.String provider)
                                 throws NoSuchAlgorithmException,
                                        NoSuchProviderException
```
    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.
    
    Parameters:
    
    algorithm - the name of the algorithm requested. See the MessageDigest Algorithms section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names. Consult the release documentation for your implementation to see which types are supported.
    
    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.
    
    java.lang.IllegalArgumentException - if the provider name is null or empty.
  - update
```
public void update(byte input)
```
    Updates the digest using the specified byte.
    
    Parameters:
    
    input - the byte with which to update the digest.
  - 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.
  - update
```
public void update(byte[] input)
```
    Updates the digest using the specified array of bytes.
    
    Parameters:
    
    input - the array of bytes.
  - digest
```
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.
  - 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.
  - digest
```
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.
  - toString
```
public java.lang.String toString()
```
    Returns a string representation of this message digest object.
    
    Overrides:
    
    toString in class java.lang.Object
  - isEqual
```
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.
  - reset
```
public void reset()
```
    Resets the digest for further use.
  - getAlgorithm
```
public final java.lang.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 Algorithms section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
    
    Returns:
    
    the name of the algorithm
  - getDigestLength
```
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.
    
    Since:
    
    1.2
  - clone
```
public java.lang.Object clone()
                       throws java.lang.CloneNotSupportedException
```
    Returns a clone if the implementation is cloneable.
    
    Overrides:
    
    clone in class MessageDigestSpi
    
    Returns:
    
    a clone if the implementation is cloneable.
    
    Throws:
    
    java.lang.CloneNotSupportedException - if this is called on an implementation that does not support Cloneable.

Class MessageDigest

Constructor Summary

Method Summary

Methods inherited from class java.security.MessageDigestSpi

Methods inherited from class java.lang.Object

Constructor Detail

MessageDigest

Method Detail

getInstance

getInstance

update

update

update

digest

digest

digest

toString

isEqual

reset

getAlgorithm

getDigestLength

clone