package javax.crypto;

import java.security.Key;
import java.security.Provider;
import java.security.SecureRandom;
import java.security.InvalidKeyException;
import java.security.NoSuchProviderException;
import java.security.NoSuchAlgorithmException;
import java.security.InvalidAlgorithmParameterException;
import java.security.spec.AlgorithmParameterSpec;

/**
 * This class provides the functionality of a key agreement (or key
 * exchange) protocol.
 * 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
 * (see <a href = "#doPhase(java.security.Key, boolean)">doPhase</a>).
 * 
 * For each of the correspondents in the key exchange, <code>doPhase</code>
 * needs to be called. For example, if this key exchange is with one other
 * party, <code>doPhase</code> needs to be called once, with the
 * <code>lastPhase</code> flag set to <code>true</code>.
 * If this key exchange is
 * with two other parties, <code>doPhase</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.
 *
 * @see KeyGenerator
 * @see SecretKey
 */
public class KeyAgreement
{
    KeyAgreementSpi keyAgreeSpi;
    Provider        provider;
    String          algorithm;

    /**
     * Creates a KeyAgreement object.
     *
     * @param keyAgreeSpi the delegate
     * @param provider the provider
     * @param algorithm the algorithm
     */
    protected KeyAgreement(
        KeyAgreementSpi keyAgreeSpi,
        Provider        provider,
        String          algorithm)
    {
        this.keyAgreeSpi = keyAgreeSpi;
        this.provider = provider;
        this.algorithm = algorithm;
    }

    /**
     * Returns the algorithm name of this <code>KeyAgreement</code> object.
     * <p>
     * This is the same name that was specified in one of the
     * <code>getInstance</code> calls that created this
     * <code>KeyAgreement</code> object.
     *
     * @return the algorithm name of this <code>KeyAgreement</code> object.
     */
    public final String getAlgorithm()
    {
        return algorithm;
    }

    /**
     * Generates a <code>KeyAgreement</code> object that implements the
     * specified key agreement algorithm.
     * If the default provider package provides an implementation of the
     * requested key agreement algorithm, an instance of
     * <code>KeyAgreement</code> containing that implementation is returned.
     * If the algorithm is not available in the default provider package,
     * other provider packages are searched.
     *
     * @param algorithm the standard name of the requested key agreement algorithm. 
     * See Appendix A in the Java Cryptography Extension API Specification &amp; Reference 
     * for information about standard algorithm names.
     * @return the new <code>KeyAgreement</code> object
     * @exception NoSuchAlgorithmException if the specified algorithm is not
     * available in the default provider package or any of the other provider
     * packages that were searched.
     */
    public static final KeyAgreement getInstance(
        String      algorithm)
    throws NoSuchAlgorithmException
    {
        try
        {
            JCEUtil.Implementation imp = JCEUtil.getImplementation("KeyAgreement", algorithm, (String) null);

            if (imp == null)
            {
                throw new NoSuchAlgorithmException(algorithm + " not found");
            }

            KeyAgreement keyAgree = new KeyAgreement((KeyAgreementSpi)imp.getEngine(), imp.getProvider(), algorithm);

            return keyAgree;
        }
        catch (NoSuchProviderException e)
        {
            throw new NoSuchAlgorithmException(algorithm + " not found");
        }
    }

    /**
     * Generates a <code>KeyAgreement</code> object for the specified key
     * agreement algorithm from the specified provider.
     *
     * @param algorithm the standard name of the requested key agreement algorithm. 
     * See Appendix A in the Java Cryptography Extension API Specification &amp; Reference 
     * for information about standard algorithm names.
     * @param provider the provider
     * @return the new <code>KeyAgreement</code> object
     * @exception NoSuchAlgorithmException if the specified algorithm is not
     * available from the specified provider.
     */
    public static final KeyAgreement getInstance(
            String      algorithm,
            Provider      provider)
        throws NoSuchAlgorithmException
    {
        if (provider == null)
        {
            throw new IllegalArgumentException("No provider specified to KeyAgreement.getInstance()");
        }

        JCEUtil.Implementation imp = JCEUtil.getImplementation("KeyAgreement", algorithm, provider);

        if (imp == null)
        {
            throw new NoSuchAlgorithmException(algorithm + " not found");
        }

        KeyAgreement keyAgree = new KeyAgreement((KeyAgreementSpi)imp.getEngine(), imp.getProvider(), algorithm);

        return keyAgree;
    }
    
    /**
     * Generates a <code>KeyAgreement</code> object for the specified key
     * agreement algorithm from the specified provider.
     *
     * @param algorithm the standard name of the requested key agreement algorithm. 
     * See Appendix A in the Java Cryptography Extension API Specification &amp; Reference 
     * for information about standard algorithm names.
     * @param provider the name of the provider
     * @return the new <code>KeyAgreement</code> object
     * @exception NoSuchAlgorithmException if the specified algorithm is not
     * available from the specified provider.
     * @exception NoSuchProviderException if the specified provider has not
     * been configured.
     */
    public static final KeyAgreement getInstance(
        String      algorithm,
        String      provider)
    throws NoSuchAlgorithmException, NoSuchProviderException
    {
        if (provider == null)
        {
            throw new IllegalArgumentException("No provider specified to KeyAgreement.getInstance()");
        }

        JCEUtil.Implementation imp = JCEUtil.getImplementation("KeyAgreement", algorithm, provider);

        if (imp == null)
        {
            throw new NoSuchAlgorithmException(algorithm + " not found");
        }

        KeyAgreement keyAgree = new KeyAgreement((KeyAgreementSpi)imp.getEngine(), imp.getProvider(), algorithm);

        return keyAgree;
    }

    /**
     * Returns the provider of this <code>KeyAgreement</code> object.
     *
     * @return the provider of this <code>KeyAgreement</code> object
     */
    public final Provider getProvider()
    {
        return provider;
    }

    /**
     * Initializes this key agreement with the given key, which is required to
     * contain all the algorithm parameters required for this key agreement.
     * <p>
     * If this key agreement requires any random bytes, it will get
     * them using the <a href="https://java.sun.com/products/jdk/1.2/docs/api/java.security.SecureRandom.html">
     * <code>SecureRandom</code></a> implementation of the highest-priority
     * installed provider as the source of randomness.
     * (If none of the installed providers supply an implementation of
     * SecureRandom, a system-provided source of randomness will be used.)
     *
     * @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.
     * @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.
     */
    public final void init(
        Key     key)
    throws InvalidKeyException
    {
        keyAgreeSpi.engineInit(key, null);
    }

    /**
     * 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.
     */
    public final void init(
        Key             key,
        SecureRandom    random)
    throws InvalidKeyException
    {
        keyAgreeSpi.engineInit(key, random);
    }

    /**
     * Initializes this key agreement with the given key and set of
     * algorithm parameters.
     * <p>
     * If this key agreement requires any random bytes, it will get
     * them using the <a href="https://java.sun.com/products/jdk/1.2/docs/api/java.security.SecureRandom.html">
     * <code>SecureRandom</code></a> implementation of the highest-priority
     * installed provider as the source of randomness.
     * (If none of the installed providers supply an implementation of
     * SecureRandom, a system-provided source of randomness will be used.)
     * 
     * @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
     * @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.
     */
    public final void init(
        Key                     key,
        AlgorithmParameterSpec  params)
    throws InvalidKeyException, InvalidAlgorithmParameterException
    {
        keyAgreeSpi.engineInit(key, params, null);
    }

    /**
     * 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.
     */
    public final void init(
        Key                     key,
        AlgorithmParameterSpec  params,
        SecureRandom            random)
    throws InvalidKeyException, InvalidAlgorithmParameterException
    {
        keyAgreeSpi.engineInit(key, params, random);
    }

    /**
     * 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.
     */
    public final Key doPhase(
        Key         key,
        boolean     lastPhase)
    throws InvalidKeyException, IllegalStateException
    {
        return keyAgreeSpi.engineDoPhase(key, lastPhase);
    }

    /**
     * Generates the shared secret and returns it in a new buffer.
     * <p>
     * This method resets this <code>KeyAgreement</code> object, so that it
     * can be reused for further key agreements. Unless this key agreement is
     * reinitialized with one of the <code>init</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
     */
    public final byte[] generateSecret()
    throws IllegalStateException
    {
        return keyAgreeSpi.engineGenerateSecret();
    }

    /**
     * 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>KeyAgreement</code> object, so that it
     * can be reused for further key agreements. Unless this key agreement is
     * reinitialized with one of the <code>init</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
     */
    public final int generateSecret(
        byte[]  sharedSecret,
        int     offset)
    throws IllegalStateException, ShortBufferException
    {
        return keyAgreeSpi.engineGenerateSecret(sharedSecret, offset);
    }

    /**
     * Creates the shared secret and returns it as a <code>SecretKey</code>
     * object of the specified algorithm.
     * <p>
     * This method resets this <code>KeyAgreement</code> object, so that it
     * can be reused for further key agreements. Unless this key agreement is
     * reinitialized with one of the <code>init</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 specified secret-key
     * algorithm is not available
     * @exception InvalidKeyException if the shared secret-key material cannot
     * be used to generate a secret key of the specified algorithm (e.g.,
     * the key material is too short)
     */
    public final SecretKey generateSecret(
        String      algorithm)
    throws IllegalStateException, NoSuchAlgorithmException, InvalidKeyException
    {
        return keyAgreeSpi.engineGenerateSecret(algorithm);
    }
}
