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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

KeyAgreementSpi()

Method Summary

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, AlgorithmParameterSpec params, SecureRandom random) Initializes this key agreement with the given key, set of algorithm parameters, and source of randomness.
protected abstract void	engineInit(Key key, SecureRandom random) Initializes this key agreement with the given key and source of randomness.

Methods inherited from class java.lang.Object

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

Constructor Detail

KeyAgreementSpi

public KeyAgreementSpi()

Method Detail

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 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 - 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, 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 - if this key agreement has not been completed yet

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, 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 - if this key agreement has not been completed yet

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, 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 - if this key agreement has not been completed yet

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)