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package javax.crypto;

import java.security.*;

import java.security.spec.*;

/**

 * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>)

 * for the <code>KeyAgreement</code> 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.

 *

 * <p> The keys involved in establishing a shared secret are created by one

 * of the

 * key generators (<code>KeyPairGenerator</code> or

 * <code>KeyGenerator</code>), a <code>KeyFactory</code>, or as a result from

 * an intermediate phase of the key agreement protocol

 * ({@link #engineDoPhase(java.security.Key, boolean) engineDoPhase}).

 *

 * <p> For each of the correspondents in the key exchange,

 * <code>engineDoPhase</code>

 * needs to be called. For example, if the key exchange is with one other

 * party, <code>engineDoPhase</code> needs to be called once, with the

 * <code>lastPhase</code> flag set to <code>true</code>.

 * If the key exchange is

 * with two other parties, <code>engineDoPhase</code> needs to be called twice,

 * the first time setting the <code>lastPhase</code> flag to

 * <code>false</code>, and the second time setting it to <code>true</code>.

 * There may be any number of parties involved in a key exchange.

 *

 * @author Jan Luehe

 *

 * @see KeyGenerator

 * @see SecretKey

 * @since 1.4

 */

public abstract class 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.

     *

     * <p> If the key agreement algorithm requires random bytes, it gets them

     * from the given source of randomness, <code>random</code>.

     * However, if the underlying

     * algorithm implementation does not require any random bytes,

     * <code>random</code> 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.

     *

     * <p>This method resets this <code>KeyAgreementSpi</code> object,

     * so that it

     * can be reused for further key agreements. Unless this key agreement is

     * reinitialized with one of the <code>engineInit</code> 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

     * <code>sharedSecret</code>, beginning at <code>offset</code> inclusive.

     *

     * <p>If the <code>sharedSecret</code> buffer is too small to hold the

     * result, a <code>ShortBufferException</code> is thrown.

     * In this case, this call should be repeated with a larger output buffer.

     *

     * <p>This method resets this <code>KeyAgreementSpi</code> object,

     * so that it

     * can be reused for further key agreements. Unless this key agreement is

     * reinitialized with one of the <code>engineInit</code> 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 <code>sharedSecret</code> where the

     * shared secret will be stored

     *

     * @return the number of bytes placed into <code>sharedSecret</code>

     *

     * @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.

     *

     * <p>This method resets this <code>KeyAgreementSpi</code> object,

     * so that it

     * can be reused for further key agreements. Unless this key agreement is

     * reinitialized with one of the <code>engineInit</code> 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;

}