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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. However, support for key exchanges with more than two parties is implementation specific or as specified by the standard key agreement algorithm.

Every implementation of the Java platform is required to support the following standard KeyAgreement algorithm:

DiffieHellman

This algorithm is described in the KeyAgreement section of the Java Security Standard Algorithm Names Specification. Consult the release documentation for your implementation to see if any other algorithms are supported.

Since:

1.4

See Also:

Constructor Summary

KeyAgreement(KeyAgreementSpi keyAgreeSpi,
 Provider provider,
 String algorithm)

Modifier	Constructor	Description
`protected`	Creates a `KeyAgreement` object.

Method Summary

Modifier and Type	Method	Description
`final 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.
`final byte[]`	`generateSecret()`	Generates the shared secret and returns it in a new buffer.
`final int`	`generateSecret(byte[] sharedSecret, int offset)`	Generates the shared secret, and places it into the buffer `sharedSecret`, beginning at `offset` inclusive.
`final SecretKey`	`generateSecret(String algorithm)`	Creates the shared secret and returns it as a `SecretKey` object of the specified algorithm.
`final String`	`getAlgorithm()`	Returns the algorithm name of this `KeyAgreement` object.
`static final KeyAgreement`	`getInstance(String algorithm)`	Returns a `KeyAgreement` object that implements the specified key agreement algorithm.
`static final KeyAgreement`	`getInstance(String algorithm, String provider)`	Returns a `KeyAgreement` object that implements the specified key agreement algorithm.
`static final KeyAgreement`	`getInstance(String algorithm, Provider provider)`	Returns a `KeyAgreement` object that implements the specified key agreement algorithm.
`final Provider`	`getProvider()`	Returns the provider of this `KeyAgreement` object.
`final 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.
`final void`	`init(Key key, SecureRandom random)`	Initializes this key agreement with the given key and source of randomness.
`final void`	`init(Key key, AlgorithmParameterSpec params)`	Initializes this key agreement with the given key and set of algorithm parameters.
`final void`	`init(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

KeyAgreement

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

Creates a KeyAgreement object.

Parameters:: keyAgreeSpi - the delegate; provider - the provider; algorithm - the algorithm

Method Details

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

Returns a KeyAgreement object that implements the specified key agreement algorithm.

This method traverses the list of registered security providers, starting with the most preferred provider. A new KeyAgreement object encapsulating the KeyAgreementSpi implementation from the first provider that supports the specified algorithm is returned.

Note that the list of registered providers may be retrieved via the Security.getProviders() method.

Implementation Note:

The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different from the order of providers returned by Security.getProviders().

Parameters:

algorithm - the standard name of the requested key agreement algorithm. See the KeyAgreement section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.

Returns:

the new KeyAgreement object

Throws:

NoSuchAlgorithmException - if no Provider supports a KeyAgreementSpi implementation for the specified algorithm

NullPointerException - if algorithm is null

See Also:

getInstance

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

Returns a KeyAgreement object that implements the specified key agreement algorithm.

A new KeyAgreement object encapsulating the KeyAgreementSpi implementation from the specified provider is returned. The specified provider must be registered in the security provider list.

Note that the list of registered providers may be retrieved via the Security.getProviders() method.

Parameters:

provider - the name of the provider.

Returns:

the new KeyAgreement object

Throws:

IllegalArgumentException - if the provider is null or empty

NoSuchAlgorithmException - if a KeyAgreementSpi implementation for the specified algorithm is not available from the specified provider

NoSuchProviderException - if the specified provider is not registered in the security provider list

NullPointerException - if algorithm is null

See Also:

getInstance

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

Returns a KeyAgreement object that implements the specified key agreement algorithm.

A new KeyAgreement object encapsulating the KeyAgreementSpi implementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.

Parameters:

provider - the provider.

Returns:

the new KeyAgreement object

Throws:

IllegalArgumentException - if the provider is null

NoSuchAlgorithmException - if a KeyAgreementSpi implementation for the specified algorithm is not available from the specified Provider object

NullPointerException - if algorithm is null

See Also:

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.

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 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 KeyAgreement 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

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.

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

generateSecret

public final SecretKey generateSecret(String algorithm) throws IllegalStateException, NoSuchAlgorithmException, InvalidKeyException

Creates the shared secret and returns it as a SecretKey object of the specified algorithm.

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 specified secret-key algorithm is not available; InvalidKeyException - if the shared secret-key material cannot be used to generate a secret key of the specified algorithm (e.g., the key material is too short)

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