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package javax.crypto;

import java.security.*;
import 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
See Also:
KeyGenerator
SecretKey
Since:
1.4/**
 * 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.
 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.
Params:
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./**
     * 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.
Params:
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./**
     * 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.
Params:
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.
Throws:
InvalidKeyException – if the given key is inappropriate for
this phase.
IllegalStateException – if this key agreement has not been
initialized.
Returns:
the (intermediate) key resulting from this phase, or null if
this phase does not yield a key/**
     * 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.
Throws:
IllegalStateException – if this key agreement has not been
completed yet
Returns:
the new buffer with the shared secret/**
     * 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
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.
Params:
sharedSecret – the buffer for the shared secret
offset – the offset in sharedSecret where the
shared secret will be stored
Throws:
IllegalStateException – if this key agreement has not been
completed yet
ShortBufferException – if the given output buffer is too small
to hold the secret
Returns:
the number of bytes placed into sharedSecret/**
     * 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.
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.
Params:
algorithm – the requested secret key algorithm
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)
Returns:
the shared secret key/**
     * 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;
}