# MessageDigest

public abstract class **MessageDigest** extends [MessageDigestSpi](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html)  
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 `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#update(byte)`
methods. At any point `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#reset()` can be called
to reset the digest. Once all the data to be updated has been
updated, one of the `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#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](https://developers.google.com/j2objc/javadoc/jre/technotes/guides/security/StandardNames.html#MessageDigest) of the Java Cryptography Architecture Standard Algorithm Name Documentation.

<br />

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/DigestInputStream.html`
- `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/DigestOutputStream.html`

### Protected Constructor Summary

|---|---|
|   | [MessageDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#MessageDigest(java.lang.String))([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) algorithm) Creates a message digest with the specified algorithm name. |

### Public Method Summary

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#clone())() Returns a clone if the implementation is cloneable. |
| int | [digest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#digest(byte[],%20int,%20int))(byte\[\] buf, int offset, int len) Completes the hash computation by performing final operations such as padding. |
| byte\[\] | [digest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#digest())() Completes the hash computation by performing final operations such as padding. |
| byte\[\] | [digest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#digest(byte[]))(byte\[\] input) Performs a final update on the digest using the specified array of bytes, then completes the digest computation. |
| final [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [getAlgorithm](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#getAlgorithm())() Returns a string that identifies the algorithm, independent of implementation details. |
| final int | [getDigestLength](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#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](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html) | [getInstance](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#getInstance(java.lang.String))([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) algorithm) Returns a MessageDigest object that implements the specified digest algorithm. |
| static [MessageDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html) | [getInstance](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#getInstance(java.lang.String,%20java.lang.String))([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) algorithm, [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) provider) Returns a MessageDigest object that implements the specified digest algorithm. |
| static [MessageDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html) | [getInstance](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#getInstance(java.lang.String,%20java.security.Provider))([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) algorithm, [Provider](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Provider.html) provider) Returns a MessageDigest object that implements the specified digest algorithm. |
| final [Provider](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Provider.html) | [getProvider](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#getProvider())() Returns the provider of this message digest object. |
| static boolean | [isEqual](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#isEqual(byte[],%20byte[]))(byte\[\] digesta, byte\[\] digestb) Compares two digests for equality. |
| void | [reset](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#reset())() Resets the digest for further use. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#toString())() Returns a string representation of this message digest object. |
| void | [update](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#update(byte[]))(byte\[\] input) Updates the digest using the specified array of bytes. |
| void | [update](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#update(byte[],%20int,%20int))(byte\[\] input, int offset, int len) Updates the digest using the specified array of bytes, starting at the specified offset. |
| final void | [update](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#update(java.nio.ByteBuffer))([ByteBuffer](https://developers.google.com/j2objc/javadoc/jre/reference/java/nio/ByteBuffer.html) input) Update the digest using the specified ByteBuffer. |
| void | [update](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#update(byte))(byte input) Updates the digest using the specified byte. |

### Inherited Method Summary

From class [java.security.MessageDigestSpi](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html)

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#clone())() Returns a clone if the implementation is cloneable. |
| int | [engineDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineDigest(byte[],%20int,%20int))(byte\[\] buf, int offset, int len) Completes the hash computation by performing final operations such as padding. |
| abstract byte\[\] | [engineDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineDigest())() Completes the hash computation by performing final operations such as padding. |
| int | [engineGetDigestLength](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineGetDigestLength())() Returns the digest length in bytes. |
| abstract void | [engineReset](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineReset())() Resets the digest for further use. |
| void | [engineUpdate](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineUpdate(java.nio.ByteBuffer))([ByteBuffer](https://developers.google.com/j2objc/javadoc/jre/reference/java/nio/ByteBuffer.html) input) Update the digest using the specified ByteBuffer. |
| abstract void | [engineUpdate](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineUpdate(byte))(byte input) Updates the digest using the specified byte. |
| abstract void | [engineUpdate](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineUpdate(byte[],%20int,%20int))(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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#clone())() Creates and returns a copy of this `Object`. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj) Compares this instance with the specified object and indicates if they are equal. |
| void | [finalize](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#finalize())() Invoked when the garbage collector has detected that this instance is no longer reachable. |
| final [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> | [getClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#getClass())() Returns the unique instance of `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html` that represents this object's class. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode())() Returns an integer hash code for this object. |
| final void | [notify](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#toString())() Returns a string containing a concise, human-readable description of this object. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long,%20int))(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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long))(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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait())() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object. |

## Protected Constructors

#### protected
**MessageDigest**
([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) 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](https://developers.google.com/j2objc/javadoc/jre/technotes/guides/security/StandardNames.html#MessageDigest) for information about standard algorithm names. |
|---|---|

## Public Methods

#### public [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)
**clone**
()

Returns a clone if the implementation is cloneable.

##### Returns

- a clone if the implementation is cloneable.

##### Throws

| [CloneNotSupportedException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/CloneNotSupportedException.html) | 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](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/DigestException.html) | 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 `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#update(byte[])`,
passing the *input* array to the `update` method,
then calls `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html#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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html)
**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](https://developers.google.com/j2objc/javadoc/jre/technotes/guides/security/StandardNames.html#MessageDigest)
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](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html)
**getInstance**
([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) 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 `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Security.html#getProviders()` method.

##### Parameters

| algorithm | the name of the algorithm requested. See the MessageDigest section in the [Java Cryptography Architecture Standard Algorithm Name Documentation](https://developers.google.com/j2objc/javadoc/jre/technotes/guides/security/StandardNames.html#MessageDigest) for information about standard algorithm names. |
|---|---|

##### Returns

- a Message Digest object that implements the specified algorithm.

##### Throws

| [NoSuchAlgorithmException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/NoSuchAlgorithmException.html) | if no Provider supports a MessageDigestSpi implementation for the specified algorithm. |
|---|---|

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Provider.html`

#### public static [MessageDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html)
**getInstance**
([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) algorithm, [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) 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 `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Security.html#getProviders()` method.

##### Parameters

| algorithm | the name of the algorithm requested. See the MessageDigest section in the [Java Cryptography Architecture Standard Algorithm Name Documentation](https://developers.google.com/j2objc/javadoc/jre/technotes/guides/security/StandardNames.html#MessageDigest) for information about standard algorithm names. |
| provider | the name of the provider. |
|---|---|

##### Returns

- a MessageDigest object that implements the specified algorithm.

##### Throws

| [NoSuchAlgorithmException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/NoSuchAlgorithmException.html) | if a MessageDigestSpi implementation for the specified algorithm is not available from the specified provider. |
| [NoSuchProviderException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/NoSuchProviderException.html) | if the specified provider is not registered in the security provider list. |
| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if the provider name is null or empty. |
|---|---|

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Provider.html`

#### public static [MessageDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html)
**getInstance**
([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) algorithm, [Provider](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Provider.html) 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](https://developers.google.com/j2objc/javadoc/jre/technotes/guides/security/StandardNames.html#MessageDigest) for information about standard algorithm names. |
| provider | the provider. |
|---|---|

##### Returns

- a MessageDigest object that implements the specified algorithm.

##### Throws

| [NoSuchAlgorithmException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/NoSuchAlgorithmException.html) | if a MessageDigestSpi implementation for the specified algorithm is not available from the specified Provider object. |
| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if the specified provider is null. |
|---|---|

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Provider.html`

#### public final [Provider](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Provider.html)
**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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html)
**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](https://developers.google.com/j2objc/javadoc/jre/reference/java/nio/ByteBuffer.html) 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. |
|---|---|