# MessageDigestSpi

public abstract class **MessageDigestSpi** extends [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)  

|---|---|---|
| Known Direct Subclasses [MessageDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html) |---|---| | [MessageDigest](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigest.html) | This MessageDigest class provides applications the functionality of a message digest algorithm, such as SHA-1 or SHA-256. | |||

This class defines the *Service Provider Interface* (**SPI** )
for the `MessageDigest` class, which provides the functionality
of a message digest algorithm, such as MD5 or SHA. Message digests are
secure one-way hash functions that take arbitrary-sized data and output a
fixed-length hash value.

All the abstract methods in this class must be implemented by a
cryptographic service provider who wishes to supply the implementation
of a particular message digest algorithm.

Implementations are free to implement the Cloneable interface.

##### See Also

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

### Public Constructor Summary

|---|---|
|   | [MessageDigestSpi](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#MessageDigestSpi())() |

### 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/MessageDigestSpi.html#clone())() Returns a clone if the implementation is cloneable. |

### Protected Method Summary

|---|---|
| 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. |

### Inherited Method Summary

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. |

## Public Constructors

#### public
**MessageDigestSpi**
()

<br />

## 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`. |
|---|---|

## Protected Methods

#### protected int
**engineDigest**
(byte\[\] buf, int offset, int len)

Completes the hash computation by performing final
operations such as padding. Once `engineDigest` has
been called, the engine should be reset (see
`https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineReset()`).
Resetting is the responsibility of the
engine implementor.

This method should be abstract, but we leave it concrete for
binary compatibility. Knowledgeable providers should override this
method.

##### Parameters

| buf | the output buffer in which to store the digest |
| offset | offset to start from in the output buffer |
| len | number of bytes within buf allotted for the digest. Both this default implementation and the SUN provider do not return partial digests. The presence of this parameter is solely for consistency in our API's. If the value of this parameter is less than the actual digest length, the method will throw a DigestException. This parameter is ignored if its value is greater than or equal to the actual digest length. |
|---|---|

##### Returns

- the length of the digest stored in the output buffer.

##### Throws

| [DigestException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/DigestException.html) | if an error occurs. |
|---|---|

#### protected abstract byte\[\]
**engineDigest**
()

Completes the hash computation by performing final
operations such as padding. Once `engineDigest` has
been called, the engine should be reset (see
`https://developers.google.com/j2objc/javadoc/jre/reference/java/security/MessageDigestSpi.html#engineReset()`).
Resetting is the responsibility of the
engine implementor.

##### Returns

- the array of bytes for the resulting hash value.

#### protected int
**engineGetDigestLength**
()

Returns the digest length in bytes.

This concrete method has been added to this previously-defined
abstract class. (For backwards compatibility, it cannot be abstract.)

The default behavior is to return 0.

This method may be overridden by a provider to return the digest
length.

##### Returns

- the digest length in bytes.

#### protected abstract void
**engineReset**
()

Resets the digest for further use.

#### protected void
**engineUpdate**
([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 |
|---|---|

#### protected abstract void
**engineUpdate**
(byte input)

Updates the digest using the specified byte.

##### Parameters

| input | the byte to use for the update. |
|---|---|

#### protected abstract void
**engineUpdate**
(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 to use for the update. |
| offset | the offset to start from in the array of bytes. |
| len | the number of bytes to use, starting at `offset`. |
|---|---|