The most common form of key agreement used today is the
* Diffie-Hellman key exchange algorithm, described in PKCS #3 -
* Diffie Hellman Key Agreement Standard.
*
* @author Casey Marshall (csm@gnu.org)
* @since 1.4
* @see KeyGenerator
* @see SecretKey
*/
public class KeyAgreement
{
// Fields.
// ------------------------------------------------------------------------
private static final String SERVICE = "KeyAgreement";
/** The underlying key agreement implementation. */
private KeyAgreementSpi kaSpi;
/** The provider of this implementation. */
private Provider provider;
/** The name of this instance's algorithm. */
private String algorithm;
/** Singnals whether or not this instance has been initialized. */
private boolean virgin;
// Constructor.
// ------------------------------------------------------------------------
protected KeyAgreement(KeyAgreementSpi kaSpi, Provider provider,
String algorithm)
{
this.kaSpi = kaSpi;
this.provider = provider;
this.algorithm = algorithm;
virgin = true;
}
/**
* Get an implementation of an algorithm from the first provider that
* implements it.
*
* @param algorithm The name of the algorithm to get.
* @return The proper KeyAgreement instacne, if found.
* @throws NoSuchAlgorithmException If the specified algorithm is not
* implemented by any installed provider.
* @throws IllegalArgumentException if algorithm is
* null or is an empty string.
*/
public static final KeyAgreement getInstance(String algorithm)
throws NoSuchAlgorithmException
{
Provider[] p = Security.getProviders();
NoSuchAlgorithmException lastException = null;
for (int i = 0; i < p.length; i++)
try
{
return getInstance(algorithm, p[i]);
}
catch (NoSuchAlgorithmException x)
{
lastException = x;
}
if (lastException != null)
throw lastException;
throw new NoSuchAlgorithmException(algorithm);
}
/**
* Return an implementation of an algorithm from a named provider.
*
* @param algorithm The name of the algorithm to create.
* @param provider The name of the provider from which to get the
* implementation.
* @return The proper KeyAgreement instance, if found.
* @throws NoSuchAlgorithmException If the named provider does not implement
* the algorithm.
* @throws NoSuchProviderException If the named provider does not exist.
* @throws IllegalArgumentException if either algorithm or
* provider is null, or if
* algorithm is an empty string.
*/
public static final KeyAgreement getInstance(String algorithm, String provider)
throws NoSuchAlgorithmException, NoSuchProviderException
{
if (provider == null)
throw new IllegalArgumentException("provider MUST NOT be null");
Provider p = Security.getProvider(provider);
if (p == null)
throw new NoSuchProviderException(provider);
return getInstance(algorithm, p);
}
/**
* Return an implementation of an algorithm from a specific provider.
*
* @param algorithm The name of the algorithm to get.
* @param provider The provider from which to get the implementation.
* @return The proper KeyAgreement instance, if found.
* @throws NoSuchAlgorithmException If this provider does not implement the
* algorithm.
* @throws IllegalArgumentException if either algorithm or
* provider is null, or if
* algorithm is an empty string.
*/
public static final KeyAgreement getInstance(String algorithm,
Provider provider)
throws NoSuchAlgorithmException
{
StringBuilder sb = new StringBuilder("KeyAgreement algorithm [")
.append(algorithm).append("] from provider[")
.append(provider).append("] could not be created");
Throwable cause;
try
{
Object spi = Engine.getInstance(SERVICE, algorithm, provider);
return new KeyAgreement((KeyAgreementSpi) spi, provider, algorithm);
}
catch (InvocationTargetException x)
{
cause = x.getCause();
if (cause instanceof NoSuchAlgorithmException)
throw (NoSuchAlgorithmException) cause;
if (cause == null)
cause = x;
}
catch (ClassCastException x)
{
cause = x;
}
NoSuchAlgorithmException x = new NoSuchAlgorithmException(sb.toString());
x.initCause(cause);
throw x;
}
/**
* Do a phase in the key agreement. The number of times this method is
* called depends upon the algorithm and the number of parties
* involved, but must be called at least once with the
* lastPhase flag set to true.
*
* @param key The key for this phase.
* @param lastPhase Should be true if this will be the
* last phase before generating the shared secret.
* @return The intermediate result, or null if there is
* no intermediate result.
* @throws java.lang.IllegalStateException If this instance has not
* been initialized.
* @throws java.security.InvalidKeyException If the key is
* inappropriate for this algorithm.
*/
public final Key doPhase(Key key, boolean lastPhase)
throws IllegalStateException, InvalidKeyException
{
if (virgin)
{
throw new IllegalStateException("not initialized");
}
return kaSpi.engineDoPhase(key, lastPhase);
}
/**
* Generate the shared secret in a new byte array.
*
* @return The shared secret.
* @throws java.lang.IllegalStateException If this instnace has not
* been initialized, or if not enough calls to
* doPhase have been made.
*/
public final byte[] generateSecret() throws IllegalStateException
{
if (virgin)
{
throw new IllegalStateException("not initialized");
}
return kaSpi.engineGenerateSecret();
}
/**
* Generate the shared secret and store it into the supplied array.
*
* @param sharedSecret The array in which to store the secret.
* @param offset The index in sharedSecret to start
* storing data.
* @return The length of the shared secret, in bytes.
* @throws java.lang.IllegalStateException If this instnace has not
* been initialized, or if not enough calls to
* doPhase have been made.
* @throws javax.crypto.ShortBufferException If the supplied array is
* not large enough to store the result.
*/
public final int generateSecret(byte[] sharedSecret, int offset)
throws IllegalStateException, ShortBufferException
{
if (virgin)
{
throw new IllegalStateException("not initialized");
}
return kaSpi.engineGenerateSecret(sharedSecret, offset);
}
/**
* Generate the shared secret and return it as an appropriate {@link
* SecretKey}.
*
* @param algorithm The secret key's algorithm.
* @return The shared secret as a secret key.
* @throws java.lang.IllegalStateException If this instnace has not
* been initialized, or if not enough calls to
* doPhase have been made.
* @throws java.security.InvalidKeyException If the shared secret
* cannot be used to make a {@link SecretKey}.
* @throws java.security.NoSuchAlgorithmException If the specified
* algorithm does not exist.
*/
public final SecretKey generateSecret(String algorithm)
throws IllegalStateException, InvalidKeyException, NoSuchAlgorithmException
{
if (virgin)
{
throw new IllegalStateException("not initialized");
}
return kaSpi.engineGenerateSecret(algorithm);
}
/**
* Return the name of this key-agreement algorithm.
*
* @return The algorithm name.
*/
public final String getAlgorithm()
{
return algorithm;
}
/**
* Return the provider of the underlying implementation.
*
* @return The provider.
*/
public final Provider getProvider()
{
return provider;
}
/**
* Initialize this key agreement with a key. This method will use the
* highest-priority {@link java.security.SecureRandom} as its source
* of randomness.
*
* @param key The key, usually the user's private key.
* @throws java.security.InvalidKeyException If the supplied key is
* not appropriate.
*/
public final void init(Key key) throws InvalidKeyException
{
init(key, new SecureRandom());
}
/**
* Initialize this key agreement with a key and a source of
* randomness.
*
* @param key The key, usually the user's private key.
* @param random The source of randomness.
* @throws java.security.InvalidKeyException If the supplied key is
* not appropriate.
*/
public final void init(Key key, SecureRandom random)
throws InvalidKeyException
{
kaSpi.engineInit(key, random);
virgin = false; // w00t!
}
/**
* Initialize this key agreement with a key and parameters. This
* method will use the highest-priority {@link
* java.security.SecureRandom} as its source of randomness.
*
* @param key The key, usually the user's private key.
* @param params The algorithm parameters.
* @throws java.security.InvalidAlgorithmParameterException If the
* supplied parameters are not appropriate.
* @throws java.security.InvalidKeyException If the supplied key is
* not appropriate.
*/
public final void init(Key key, AlgorithmParameterSpec params)
throws InvalidAlgorithmParameterException, InvalidKeyException
{
init(key, params, new SecureRandom());
}
/**
* Initialize this key agreement with a key, parameters, and source of
* randomness.
*
* @param key The key, usually the user's private key.
* @param params The algorithm parameters.
* @param random The source of randomness.
* @throws java.security.InvalidAlgorithmParameterException If the
* supplied parameters are not appropriate.
* @throws java.security.InvalidKeyException If the supplied key is
* not appropriate.
*/
public final void init(Key key, AlgorithmParameterSpec params,
SecureRandom random)
throws InvalidAlgorithmParameterException, InvalidKeyException
{
kaSpi.engineInit(key, params, random);
virgin = false; // w00t!
}
}