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KeyAgreementSpi

public abstract class KeyAgreementSpi
extends Object

java.lang.Object
   ↳ javax.crypto.KeyAgreementSpi


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.

See also:

Summary

Public constructors

KeyAgreementSpi()

Protected methods

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.

abstract byte[] engineGenerateSecret()

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

abstract SecretKey engineGenerateSecret(String algorithm)

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

abstract int engineGenerateSecret(byte[] sharedSecret, int offset)

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

abstract void engineInit(Key key, SecureRandom random)

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

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.

Inherited methods

From class java.lang.Object

Public constructors

KeyAgreementSpi

Added in API level 1
KeyAgreementSpi ()

Protected methods

engineDoPhase

Added in API level 1
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.

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 or not 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
Throws
InvalidKeyException if the given key is inappropriate for this phase.
IllegalStateException if this key agreement has not been initialized.

engineGenerateSecret

Added in API level 1
byte[] engineGenerateSecret ()

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
byte[] the new buffer with the shared secret
Throws
IllegalStateException if this key agreement has not been completed yet

engineGenerateSecret

Added in API level 1
SecretKey engineGenerateSecret (String algorithm)

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 String: the requested secret key algorithm
Returns
SecretKey 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)

engineGenerateSecret

Added in API level 1
int engineGenerateSecret (byte[] sharedSecret, 
                int offset)

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 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
Throws
IllegalStateException if this key agreement has not been completed yet
ShortBufferException if the given output buffer is too small to hold the secret

engineInit

Added in API level 1
void engineInit (Key key, 
                SecureRandom random)

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
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

Added in API level 1
void engineInit (Key key, 
                AlgorithmParameterSpec params, 
                SecureRandom random)

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
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.
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