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javax.crypto

public abstract Class KeyAgreementSpi

extends Object
Class Inheritance
Known Direct Subclasses
com.sun.crypto.provider.DHKeyAgreement, sun.security.ec.ECDHKeyAgreement, sun.security.ec.XDHKeyAgreement
Imports
java.security.*, java.security.spec.*
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.

Author
Jan Luehe
Since
1.4
See Also
KeyGenerator, SecretKey

Constructor Summary

AccessConstructor and Description
public
KeyAgreementSpi()

Constructor for subclasses to call.

Method Summary

Modifier and TypeMethod and Description
protected abstract Key

Returns:

the (intermediate) key resulting from this phase, or null if this phase does not yield a key
engineDoPhase(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.
key, boolean
flag which indicates whether this is the last phase of this key agreement.
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[]

Returns:

the new buffer with the shared secret
engineGenerateSecret()

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

protected abstract int

Returns:

the number of bytes placed into sharedSecret
engineGenerateSecret(byte[]
the buffer for the shared secret
sharedSecret, int
the offset in sharedSecret where the shared secret will be stored
offset)

Generates the shared secret, and places it into the buffer sharedSecret, beginning at offset inclusive.

protected abstract SecretKey

Returns:

the shared secret key. The length of the key material may be adjusted to be compatible with the specified algorithm, regardless of whether the key is extractable. If algorithm is specified as "Generic" and it is supported by the implementation, the full shared secret is returned.
engineGenerateSecret(String
the requested secret key algorithm. This is different from the KeyAgreement algorithm provided to the getInstance method. See the SecretKey Algorithms section in the Java Security Standard Algorithm Names Specification for information about standard secret key algorithm names. Specify "Generic" if the output will be used as the input keying material of a key derivation function (KDF).
algorithm)

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

protected abstract void
engineInit(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.
key, SecureRandom
the source of randomness
random)

Initializes this key agreement with the given key and source of randomness.

protected abstract void
engineInit(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.
key, AlgorithmParameterSpec
the key agreement parameters
params, SecureRandom
the source of randomness
random)

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

Inherited from java.lang.Object:
cloneequalsfinalizegetClasshashCodenotifynotifyAlltoStringwaitwaitwait

Constructor Detail

KeyAgreementSpiback to summary
public KeyAgreementSpi()

Constructor for subclasses to call.

Method Detail

engineDoPhaseback to summary
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: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:boolean

flag which indicates whether this is the last phase of this key agreement.

Returns:Key

the (intermediate) key resulting from this phase, or null if this phase does not yield a key

Exceptions
InvalidKeyException:
if the given key is inappropriate for this phase.
IllegalStateException:
if this key agreement has not been initialized.
engineGenerateSecretback to summary
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:byte[]

the new buffer with the shared secret

Exceptions
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
engineGenerateSecretback to summary
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:byte[]

the buffer for the shared secret

offset:int

the offset in sharedSecret where the shared secret will be stored

Returns:int

the number of bytes placed into sharedSecret

Exceptions
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
engineGenerateSecretback to summary
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:String

the requested secret key algorithm. This is different from the KeyAgreement algorithm provided to the getInstance method. See the SecretKey Algorithms section in the Java Security Standard Algorithm Names Specification for information about standard secret key algorithm names. Specify "Generic" if the output will be used as the input keying material of a key derivation function (KDF).

Returns:SecretKey

the shared secret key. The length of the key material may be adjusted to be compatible with the specified algorithm, regardless of whether the key is extractable. If algorithm is specified as "Generic" and it is supported by the implementation, the full shared secret is returned.

Exceptions
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 supported
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)
External Specification
Java Security Standard Algorithm Names
engineInitback to summary
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: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:SecureRandom

the source of randomness

Exceptions
InvalidKeyException:
if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type.
engineInitback to summary
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: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:AlgorithmParameterSpec

the key agreement parameters

random:SecureRandom

the source of randomness

Exceptions
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.