javax.crypto
Class KeyAgreement

java.lang.Object
  javax.crypto.KeyAgreement

public class KeyAgreement
extends Object

This class provides the functionality of a key agreement (or key exchange) protocol. 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 For each of the correspondents in the key exchange, doPhase needs to be called. For example, if this key exchange is with one other party, doPhase needs to be called once, with the lastPhase flag set to true. If this key exchange is with two other parties, doPhase 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.

Version:

"$Id: KeyAgreement.java 1913 2007-08-08 02:41:53Z jpeters $"

Author:

Patric Kabus, Jan Peters

Field Summary

private String	algorithm_ The algorithm used by this instance.
private KeyAgreementSpi	keyAgreeSpi_ The key agreement implementation used by this instance.
private Provider	provider_ The provider used by this instance.

Constructor Summary

protected

KeyAgreement(KeyAgreementSpi keyAgreeSpi, Provider provider, String algorithm) Creates a KeyAgreement object.

Method Summary

Key	doPhase(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.
byte[]	generateSecret() Generates the shared secret and returns it in a new buffer.
int	generateSecret(byte[] sharedSecret, int offset) Generates the shared secret, and places it into the buffer sharedSecret, beginning at offset inclusive.
SecretKey	generateSecret(String algorithm) Creates the shared secret and returns it as a secret key object of the requested algorithm type.
String	getAlgorithm() Returns the algorithm name of this KeyAgreement object.
static KeyAgreement	getInstance(String algorithm) Generates a KeyAgreement object that implements the specified key agreement algorithm.
static KeyAgreement	getInstance(String algorithm, Provider provider) Generates a KeyAgreement object for the specified key agreement algorithm from the specified provider.
static KeyAgreement	getInstance(String algorithm, String provider) Generates a KeyAgreement object for the specified key agreement algorithm from the specified provider.
Provider	getProvider() Returns the provider of this KeyAgreement object.
void	init(Key key) Initializes this key agreement with the given key, which is required to contain all the algorithm parameters required for this key agreement.
void	init(Key key, AlgorithmParameterSpec params) Initializes this key agreement with the given key and set of algorithm parameters.
void	init(Key key, AlgorithmParameterSpec params, SecureRandom random) Initializes this key agreement with the given key, set of algorithm parameters, and source of randomness.
void	init(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

Field Detail

keyAgreeSpi_

private KeyAgreementSpi keyAgreeSpi_

The key agreement implementation used by this instance.

provider_

private Provider provider_

The provider used by this instance.

algorithm_

private String algorithm_

The algorithm used by this instance.

Constructor Detail

KeyAgreement

protected KeyAgreement(KeyAgreementSpi keyAgreeSpi,
                       Provider provider,
                       String algorithm)

Creates a KeyAgreement object.

Parameters:

keyAgreeSpi - the delegate.

provider - the provider.

algorithm - the algoritm.

Method Detail

getAlgorithm

public final String getAlgorithm()

Returns the algorithm name of this KeyAgreement object.

This is the same name that was specified in one of the getInstance calls that created this KeyAgreement object.

Returns:

the algorithm name of this KeyAgreement object.

getInstance

public static final KeyAgreement getInstance(String algorithm)
                                      throws NoSuchAlgorithmException

Generates a KeyAgreement object that implements the specified key agreement algorithm. If the default provider package provides an implementation of the requested key agreement algorithm, an instance of KeyAgreement containing that implementation is returned. If the algorithm is not available in the default provider package, other provider packages are searche

Parameters:

algorithm - the standard name of the requested key agreement algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.

Returns:

the new KeyAgreement object

Throws:

NoSuchAlgorithmException - if the specified algorithm is not available in the default provider package or any of the other provider packages that were searched.

NullPointerException - if the specified algorithm is null.

getInstance

public static final KeyAgreement getInstance(String algorithm,
                                             String provider)
                                      throws NoSuchAlgorithmException,
                                             NoSuchProviderException

Generates a KeyAgreement object for the specified key agreement algorithm from the specified provider.

Parameters:

algorithm - the standard name of the requested key agreement algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.

provider - the name of the provider

Returns:

the new KeyAgreement object

Throws:

IllegalArgumentException - if the provider is null.

NoSuchAlgorithmException - if the specified algorithm is not available from the specified provider.

NoSuchProviderException - if the specified provider has not been configured.

NullPointerException - if the specified algorithm is null.

getInstance

public static final KeyAgreement getInstance(String algorithm,
                                             Provider provider)
                                      throws NoSuchAlgorithmException

Generates a KeyAgreement object for the specified key agreement algorithm from the specified provider. Note: the provider doesn't have to be registered.

Parameters:

algorithm - the standard name of the requested key agreement algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.

provider - the provider

Returns:

the new KeyAgreement object

Throws:

IllegalArgumentException - if the provider is null.

NoSuchAlgorithmException - if the specified algorithm is not available from the specified provider.

NullPointerException - if the specified algorithm is null.

getProvider

public final Provider getProvider()

Returns the provider of this KeyAgreement object.

Returns:

the provider of this KeyAgreement object.

init

public final void init(Key key)
                throws InvalidKeyException

Initializes this key agreement with the given key, which is required to contain all the algorithm parameters required for this key agreement.

If this key agreement requires any random bytes, it will get them using the SecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness will be used.)

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.

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.

init

public final void init(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.

init

public final void init(Key key,
                       AlgorithmParameterSpec params)
                throws InvalidKeyException,
                       InvalidAlgorithmParameterException

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

If this key agreement requires any random bytes, it will get them using the SecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness will be used.)

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.

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.

init

public final void init(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.

doPhase

public final Key doPhase(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.

generateSecret

public final byte[] generateSecret()
                            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.

generateSecret

public final int generateSecret(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 init 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.

generateSecret

public final SecretKey generateSecret(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).