Module java.base

Package javax.crypto

Class KeyAgreementSpi

java.lang.Object

javax.crypto.KeyAgreementSpi

public abstract class KeyAgreementSpi
extends Object

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 (engineDoPhase).

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.

Since:

1.4

See Also:

• KeyGenerator
• SecretKey

Constructor Summary

Constructors

Constructor	Description
KeyAgreementSpi()	Constructor for subclasses to call.

Method Summary

Modifier and Type	Method	Description
protected abstract Key	engineDoPhase(Key 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.
protected abstract byte[]	engineGenerateSecret()	Generates the shared secret and returns it in a new buffer.
protected abstract int	engineGenerateSecret(byte[] sharedSecret, int offset)	Generates the shared secret, and places it into the buffer sharedSecret, beginning at offset inclusive.
protected abstract SecretKey	engineGenerateSecret(String algorithm)	Creates the shared secret and returns it as a secret key object of the requested algorithm type.
protected abstract void	engineInit(Key key, SecureRandom random)	Initializes this key agreement with the given key and source of randomness.
protected abstract void	engineInit(Key key, AlgorithmParameterSpec params, SecureRandom random)	Initializes this key agreement with the given key, set of algorithm parameters, and source of randomness.

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

KeyAgreementSpi

public KeyAgreementSpi()

Constructor for subclasses to call.

Method Details

engineInit

protected abstract void engineInit(Key key,
 SecureRandom random)
                            throws InvalidKeyException

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 - if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type.

engineInit

protected abstract void engineInit(Key key,
 AlgorithmParameterSpec params,
 SecureRandom random)
                            throws InvalidKeyException,
InvalidAlgorithmParameterException

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 - if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type.

InvalidAlgorithmParameterException - if the given parameters are inappropriate for this key agreement.

engineDoPhase

protected abstract Key engineDoPhase(Key key,
 boolean lastPhase)
                              throws InvalidKeyException,
IllegalStateException

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 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 - if the given key is inappropriate for this phase.

IllegalStateException - if this key agreement has not been initialized.

engineGenerateSecret

protected abstract byte[] engineGenerateSecret()
                                        throws IllegalStateException

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

This method resets this KeyAgreementSpi object to the state that it was in after the most recent call to one of the init methods. After a call to generateSecret, the object can be reused for further key agreement operations by calling doPhase to supply new keys, and then calling generateSecret to produce a new secret. In this case, the private information and algorithm parameters supplied to init will be used for multiple key agreement operations. The init method can be called after generateSecret to change the private information used in subsequent operations.

Returns:

the new buffer with the shared secret

Throws:

IllegalStateException - if this key agreement has not been initialized or if doPhase has not been called to supply the keys for all parties in the agreement

engineGenerateSecret

protected abstract int engineGenerateSecret(byte[] sharedSecret,
 int offset)
                                     throws IllegalStateException,
ShortBufferException

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 to the state that it was in after the most recent call to one of the init methods. After a call to generateSecret, the object can be reused for further key agreement operations by calling doPhase to supply new keys, and then calling generateSecret to produce a new secret. In this case, the private information and algorithm parameters supplied to init will be used for multiple key agreement operations. The init method can be called after generateSecret to change the private information used in subsequent operations.

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 - if this key agreement has not been initialized or if doPhase has not been called to supply the keys for all parties in the agreement

ShortBufferException - if the given output buffer is too small to hold the secret

engineGenerateSecret

protected abstract SecretKey engineGenerateSecret(String algorithm)
                                           throws IllegalStateException,
NoSuchAlgorithmException,
InvalidKeyException

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

This method resets this KeyAgreementSpi object to the state that it was in after the most recent call to one of the init methods. After a call to generateSecret, the object can be reused for further key agreement operations by calling doPhase to supply new keys, and then calling generateSecret to produce a new secret. In this case, the private information and algorithm parameters supplied to init will be used for multiple key agreement operations. The init method can be called after generateSecret to change the private information used in subsequent operations.

Parameters:

algorithm - the requested secret key algorithm

Returns:

the shared secret key

Throws:

IllegalStateException - if this key agreement has not been initialized or if doPhase has not been called to supply the keys for all parties in the agreement

NoSuchAlgorithmException - if the requested secret key algorithm is not available

InvalidKeyException - 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)