# KeyAgreementSpi

public abstract class **KeyAgreementSpi** extends [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)  
This class defines the *Service Provider Interface* (**SPI** )
for the `KeyAgreement` class.
All the abstract methods in this class must be implemented by each
cryptographic service provider who wishes to supply the implementation
of a particular key agreement algorithm.

The keys involved in establishing a shared secret are created by one
of the
key generators (`KeyPairGenerator` or
`KeyGenerator`), a `KeyFactory`, or as a result from
an intermediate phase of the key agreement protocol
(`https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyAgreementSpi.html#engineDoPhase(java.security.Key,%20boolean)`).

For each of the correspondents in the key exchange,
`engineDoPhase`
needs to be called. For example, if the key exchange is with one other
party, `engineDoPhase` needs to be called once, with the
`lastPhase` flag set to `true`.
If the key exchange is
with two other parties, `engineDoPhase` needs to be called twice,
the first time setting the `lastPhase` flag to
`false`, and the second time setting it to `true`.
There may be any number of parties involved in a key exchange.

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyGenerator.html`
- `https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/SecretKey.html`

### Public Constructor Summary

|---|---|
|   | [KeyAgreementSpi](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyAgreementSpi.html#KeyAgreementSpi())() |

### Protected Method Summary

|---|---|
| abstract [Key](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Key.html) | [engineDoPhase](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyAgreementSpi.html#engineDoPhase(java.security.Key,%20boolean))([Key](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Key.html) key, boolean lastPhase) Executes the next phase of this key agreement with the given key that was received from one of the other parties involved in this key agreement. |
| abstract byte\[\] | [engineGenerateSecret](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyAgreementSpi.html#engineGenerateSecret())() Generates the shared secret and returns it in a new buffer. |
| abstract [SecretKey](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/SecretKey.html) | [engineGenerateSecret](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyAgreementSpi.html#engineGenerateSecret(java.lang.String))([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) algorithm) Creates the shared secret and returns it as a secret key object of the requested algorithm type. |
| abstract int | [engineGenerateSecret](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyAgreementSpi.html#engineGenerateSecret(byte[],%20int))(byte\[\] sharedSecret, int offset) Generates the shared secret, and places it into the buffer `sharedSecret`, beginning at `offset` inclusive. |
| abstract void | [engineInit](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyAgreementSpi.html#engineInit(java.security.Key,%20java.security.SecureRandom))([Key](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Key.html) key, [SecureRandom](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/SecureRandom.html) random) Initializes this key agreement with the given key and source of randomness. |
| abstract void | [engineInit](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/KeyAgreementSpi.html#engineInit(java.security.Key,%20java.security.spec.AlgorithmParameterSpec,%20java.security.SecureRandom))([Key](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Key.html) key, [AlgorithmParameterSpec](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/spec/AlgorithmParameterSpec.html) params, [SecureRandom](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/SecureRandom.html) random) Initializes this key agreement with the given key, set of algorithm parameters, and source of randomness. |

### 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
**KeyAgreementSpi**
()

<br />

## Protected Methods

#### protected abstract [Key](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Key.html)
**engineDoPhase**
([Key](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Key.html) key, boolean lastPhase)

Executes the next phase of this key agreement with the given
key that was received from one of the other parties involved in this key
agreement.

##### Parameters

| key | the key for this phase. For example, in the case of Diffie-Hellman between 2 parties, this would be the other party's Diffie-Hellman public key. |
| lastPhase | flag which indicates whether or not this is the last phase of this key agreement. |
|---|---|

##### Returns

- the (intermediate) key resulting from this phase, or null if this phase does not yield a key

##### Throws

| [InvalidKeyException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/InvalidKeyException.html) | if the given key is inappropriate for this phase. |
| [IllegalStateException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalStateException.html) | if this key agreement has not been initialized. |
|---|---|

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

Generates the shared secret and returns it in a new buffer.

This method resets this `KeyAgreementSpi` object,
so that it
can be reused for further key agreements. Unless this key agreement is
reinitialized with one of the `engineInit` methods, the same
private information and algorithm parameters will be used for
subsequent key agreements.

##### Returns

- the new buffer with the shared secret

##### Throws

| [IllegalStateException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalStateException.html) | if this key agreement has not been completed yet |
|---|---|

#### protected abstract [SecretKey](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/SecretKey.html)
**engineGenerateSecret**
([String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) algorithm)

Creates the shared secret and returns it as a secret key object
of the requested algorithm type.

This method resets this `KeyAgreementSpi` object,
so that it
can be reused for further key agreements. Unless this key agreement is
reinitialized with one of the `engineInit` methods, the same
private information and algorithm parameters will be used for
subsequent key agreements.

##### Parameters

| algorithm | the requested secret key algorithm |
|---|---|

##### Returns

- the shared secret key

##### Throws

| [IllegalStateException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalStateException.html) | if this key agreement has not been completed yet |
| [NoSuchAlgorithmException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/NoSuchAlgorithmException.html) | if the requested secret key algorithm is not available |
| [InvalidKeyException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/InvalidKeyException.html) | if the shared secret key material cannot be used to generate a secret key of the requested algorithm type (e.g., the key material is too short) |
|---|---|

#### protected abstract int
**engineGenerateSecret**
(byte\[\] sharedSecret, int offset)

Generates the shared secret, and places it into the buffer
`sharedSecret`, beginning at `offset` inclusive.

If the `sharedSecret` buffer is too small to hold the
result, a `ShortBufferException` is thrown.
In this case, this call should be repeated with a larger output buffer.

This method resets this `KeyAgreementSpi` object,
so that it
can be reused for further key agreements. Unless this key agreement is
reinitialized with one of the `engineInit` methods, the same
private information and algorithm parameters will be used for
subsequent key agreements.

##### Parameters

| sharedSecret | the buffer for the shared secret |
| offset | the offset in `sharedSecret` where the shared secret will be stored |
|---|---|

##### Returns

- the number of bytes placed into `sharedSecret`

##### Throws

| [IllegalStateException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalStateException.html) | if this key agreement has not been completed yet |
| [ShortBufferException](https://developers.google.com/j2objc/javadoc/jre/reference/javax/crypto/ShortBufferException.html) | if the given output buffer is too small to hold the secret |
|---|---|

#### protected abstract void
**engineInit**
([Key](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Key.html) key, [SecureRandom](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/SecureRandom.html) random)

Initializes this key agreement with the given key and source of
randomness. The given key is required to contain all the algorithm
parameters required for this key agreement.

If the key agreement algorithm requires random bytes, it gets them
from the given source of randomness, `random`.
However, if the underlying
algorithm implementation does not require any random bytes,
`random` is ignored.

##### Parameters

| key | the party's private information. For example, in the case of the Diffie-Hellman key agreement, this would be the party's own Diffie-Hellman private key. |
| random | the source of randomness |
|---|---|

##### Throws

| [InvalidKeyException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/InvalidKeyException.html) | if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type. |
|---|---|

#### protected abstract void
**engineInit**
([Key](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/Key.html) key, [AlgorithmParameterSpec](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/spec/AlgorithmParameterSpec.html) params, [SecureRandom](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/SecureRandom.html) random)

Initializes this key agreement with the given key, set of
algorithm parameters, and source of randomness.

##### Parameters

| key | the party's private information. For example, in the case of the Diffie-Hellman key agreement, this would be the party's own Diffie-Hellman private key. |
| params | the key agreement parameters |
| random | the source of randomness |
|---|---|

##### Throws

| [InvalidKeyException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/InvalidKeyException.html) | if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type. |
| [InvalidAlgorithmParameterException](https://developers.google.com/j2objc/javadoc/jre/reference/java/security/InvalidAlgorithmParameterException.html) | if the given parameters are inappropriate for this key agreement. |
|---|---|