Class 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.

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 Cryptography Architecture Standard Algorithm Name Documentation. Consult the release documentation for your implementation to see if any other algorithms are supported.
Since:
1.4
See Also:
KeyGenerator, SecretKey

Constructors

Modifier Constructor and Description
protected KeyAgreement(KeyAgreementSpi keyAgreeSpi, Provider provider, String algorithm)

Creates a KeyAgreement object.

Methods

Modifier and Type Method and Description
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 SecretKey object of the specified algorithm.
String getAlgorithm()

Returns the algorithm name of this KeyAgreement object.
static KeyAgreement getInstance(String algorithm)

Returns a KeyAgreement object that implements the specified key agreement algorithm.
static KeyAgreement getInstance(String algorithm, Provider provider)

Returns a KeyAgreement object that implements the specified key agreement algorithm.
static KeyAgreement getInstance(String algorithm, String provider)

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

Constructors

KeyAgreement

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

Creates a KeyAgreement object.

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

Methods

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.

Parameters:
algorithm - the standard name of the requested key agreement algorithm. See the KeyAgreement section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
Returns:
the new KeyAgreement object.
Throws:
NullPointerException - if the specified algorithm is null.
NoSuchAlgorithmException - if no Provider supports a KeyAgreementSpi implementation for the specified algorithm.
See Also:
Provider

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:
algorithm - the standard name of the requested key agreement algorithm. See the KeyAgreement section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider - the name of the provider.
Returns:
the new KeyAgreement object.
Throws:
NullPointerException - if the specified algorithm is null.
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.
IllegalArgumentException - if the provider is null or empty.
See Also:
Provider

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 object is returned. Note that the specified Provider object does not have to be registered in the provider list.

Parameters:
algorithm - the standard name of the requested key agreement algorithm. See the KeyAgreement section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider - the provider.
Returns:
the new KeyAgreement object.
Throws:
NullPointerException - if the specified algorithm is null.
NoSuchAlgorithmException - if a KeyAgreementSpi implementation for the specified algorithm is not available from the specified Provider object.
IllegalArgumentException - if the provider is null.
See Also:
Provider

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 KeyAgreement 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.

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 KeyAgreement 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 SecretKey object of the specified algorithm.

This method resets this KeyAgreement 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:
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 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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