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 (see 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 KeyGenerator
* @see SecretKey
*/
public abstract class KeyAgreementSpi
{
public KeyAgreementSpi()
{
}
/**
* 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.
*
* @param 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.
* @param random the source of randomness
* @exception InvalidKeyException if the given key is inappropriate for this key agreement, e.g., is
* of the wrong type or has an incompatible algorithm type.
*/
protected abstract void engineInit(
Key key,
SecureRandom random)
throws InvalidKeyException;
/**
* Initializes this key agreement with the given key, set of
* algorithm parameters, and source of randomness.
*
* @param 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.
* @param params the key agreement parameters
* @param random the source of randomness
* @exception InvalidKeyException if the given key is inappropriate for this key agreement, e.g., is of the
* wrong type or has an incompatible algorithm type.
* @exception InvalidAlgorithmParameterException if the given parameters are inappropriate for this key
* agreement.
*/
protected abstract void engineInit(
Key key,
AlgorithmParameterSpec params,
SecureRandom random)
throws InvalidKeyException, InvalidAlgorithmParameterException;
/**
* 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.
* @param 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.
* @param lastPhase flag which indicates whether or not this is the last
* phase of this key agreement.
* @return the (intermediate) key resulting from this phase, or null if this phase does not yield a key
* @exception InvalidKeyException if the given key is inappropriate for this phase.
* @exception IllegalStateException if this key agreement has not been initialized.
*/
protected abstract Key engineDoPhase(
Key key,
boolean lastPhase)
throws InvalidKeyException, 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.
* @return the new buffer with the shared secret
* @exception IllegalStateException if this key agreement has not been completed yet
*/
protected abstract byte[] engineGenerateSecret()
throws IllegalStateException;
/**
* 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.
*
* @param sharedSecret the buffer for the shared secret
* @param offset the offset in sharedSecret where the shared secret will be stored
* @return the number of bytes placed into sharedSecret
* @exception IllegalStateException if this key agreement has not been completed yet
* @exception ShortBufferException if the given output buffer is too small to hold the secret
*/
protected abstract int engineGenerateSecret(
byte[] sharedSecret,
int offset)
throws IllegalStateException, ShortBufferException;
/**
* 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.
*
* @param algorithm the requested secret key algorithm
* @return the shared secret key
* @exception IllegalStateException if this key agreement has not been completed yet
* @exception NoSuchAlgorithmException if the requested secret key algorithm is not available
* @exception 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)
*/
protected abstract SecretKey engineGenerateSecret(
String algorithm)
throws IllegalStateException, NoSuchAlgorithmException, InvalidKeyException;
}