Key) into key specifications
* (transparent representations of the underlying key material), and vice
* versa.
*
* Key factories are bi-directional. That is, they allow you to build an * opaque key object from a given key specification (key material), or to * retrieve the underlying key material of a key object in a suitable format. * *
Multiple compatible key specifications may exist for the same key.
* For example, a DSA public key may be specified using
* DSAPublicKeySpec or
* X509EncodedKeySpec. A key factory can be used to translate
* between compatible key specifications.
*
*
The following is an example of how to use a key factory in order to * instantiate a DSA public key from its encoding. * Assume Alice has received a digital signature from Bob. * Bob also sent her his public key (in encoded format) to verify * his signature. Alice then performs the following actions: * *
* X509EncodedKeySpec bobPubKeySpec = new X509EncodedKeySpec(bobEncodedPubKey);
* KeyFactory keyFactory = KeyFactory.getInstance("DSA");
* PublicKey bobPubKey = keyFactory.generatePublic(bobPubKeySpec);
* Signature sig = Signature.getInstance("DSA");
* sig.initVerify(bobPubKey);
* sig.update(data);
* sig.verify(signature);
*
*
* Android provides the following KeyFactory algorithms:
*
| Name | *Supported (API Levels) | *
|---|---|
| DH | *1+ | *
| DSA | *1+ | *
| EC | *11+ | *
| RSA | *1+ | *
| X.509 | *1–8 | *
This method traverses the list of registered security Providers, * starting with the most preferred Provider. * A new KeyFactory object encapsulating the * KeyFactorySpi implementation from the first * Provider that supports the specified algorithm is returned. * *
Note that the list of registered providers may be retrieved via * the {@link Security#getProviders() Security.getProviders()} method. * * @param algorithm the name of the requested key algorithm. * See the KeyFactory section in the * Java Cryptography Architecture Standard Algorithm Name Documentation * for information about standard algorithm names. * * @return the new KeyFactory object. * * @exception NoSuchAlgorithmException if no Provider supports a * KeyFactorySpi implementation for the * specified algorithm. * * @see Provider */ public static KeyFactory getInstance(String algorithm) throws NoSuchAlgorithmException { return new KeyFactory(algorithm); } /** * Returns a KeyFactory object that converts * public/private keys of the specified algorithm. * *
A new KeyFactory object encapsulating the * KeyFactorySpi implementation from the specified provider * is returned. The specified provider must be registered * in the security provider list. * *
Note that the list of registered providers may be retrieved via * the {@link Security#getProviders() Security.getProviders()} method. * * @param algorithm the name of the requested key algorithm. * See the KeyFactory section in the * Java Cryptography Architecture Standard Algorithm Name Documentation * for information about standard algorithm names. * * @param provider the name of the provider. * * @return the new KeyFactory object. * * @exception NoSuchAlgorithmException if a KeyFactorySpi * implementation for the specified algorithm is not * available from the specified provider. * * @exception NoSuchProviderException if the specified provider is not * registered in the security provider list. * * @exception IllegalArgumentException if the provider name is null * or empty. * * @see Provider */ public static KeyFactory getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException { Instance instance = GetInstance.getInstance("KeyFactory", KeyFactorySpi.class, algorithm, provider); return new KeyFactory((KeyFactorySpi)instance.impl, instance.provider, algorithm); } /** * Returns a KeyFactory object that converts * public/private keys of the specified algorithm. * *
A new KeyFactory object encapsulating the
* KeyFactorySpi implementation from the specified Provider
* object is returned. Note that the specified Provider object
* does not have to be registered in the provider list.
*
* @param algorithm the name of the requested key algorithm.
* See the KeyFactory section in the
* Java Cryptography Architecture Standard Algorithm Name Documentation
* for information about standard algorithm names.
*
* @param provider the provider.
*
* @return the new KeyFactory object.
*
* @exception NoSuchAlgorithmException if a KeyFactorySpi
* implementation for the specified algorithm is not available
* from the specified Provider object.
*
* @exception IllegalArgumentException if the specified provider is null.
*
* @see Provider
*
* @since 1.4
*/
public static KeyFactory getInstance(String algorithm, Provider provider)
throws NoSuchAlgorithmException {
Instance instance = GetInstance.getInstance("KeyFactory",
KeyFactorySpi.class, algorithm, provider);
return new KeyFactory((KeyFactorySpi)instance.impl,
instance.provider, algorithm);
}
/**
* Returns the provider of this key factory object.
*
* @return the provider of this key factory object
*/
public final Provider getProvider() {
synchronized (lock) {
// disable further failover after this call
serviceIterator = null;
return provider;
}
}
/**
* Gets the name of the algorithm
* associated with this KeyFactory.
*
* @return the name of the algorithm associated with this
* KeyFactory
*/
public final String getAlgorithm() {
return this.algorithm;
}
/**
* Update the active KeyFactorySpi of this class and return the next
* implementation for failover. If no more implemenations are
* available, this method returns null. However, the active spi of
* this class is never set to null.
*/
private KeyFactorySpi nextSpi(KeyFactorySpi oldSpi) {
synchronized (lock) {
// somebody else did a failover concurrently
// try that spi now
if ((oldSpi != null) && (oldSpi != spi)) {
return spi;
}
if (serviceIterator == null) {
return null;
}
while (serviceIterator.hasNext()) {
Service s = serviceIterator.next();
try {
Object obj = s.newInstance(null);
if (obj instanceof KeyFactorySpi == false) {
continue;
}
KeyFactorySpi spi = (KeyFactorySpi)obj;
provider = s.getProvider();
this.spi = spi;
return spi;
} catch (NoSuchAlgorithmException e) {
// ignore
}
}
serviceIterator = null;
return null;
}
}
/**
* Generates a public key object from the provided key specification
* (key material).
*
* @param keySpec the specification (key material) of the public key.
*
* @return the public key.
*
* @exception InvalidKeySpecException if the given key specification
* is inappropriate for this key factory to produce a public key.
*/
public final PublicKey generatePublic(KeySpec keySpec)
throws InvalidKeySpecException {
if (serviceIterator == null) {
return spi.engineGeneratePublic(keySpec);
}
Exception failure = null;
KeyFactorySpi mySpi = spi;
do {
try {
return mySpi.engineGeneratePublic(keySpec);
} catch (Exception e) {
if (failure == null) {
failure = e;
}
mySpi = nextSpi(mySpi);
}
} while (mySpi != null);
if (failure instanceof RuntimeException) {
throw (RuntimeException)failure;
}
if (failure instanceof InvalidKeySpecException) {
throw (InvalidKeySpecException)failure;
}
throw new InvalidKeySpecException
("Could not generate public key", failure);
}
/**
* Generates a private key object from the provided key specification
* (key material).
*
* @param keySpec the specification (key material) of the private key.
*
* @return the private key.
*
* @exception InvalidKeySpecException if the given key specification
* is inappropriate for this key factory to produce a private key.
*/
public final PrivateKey generatePrivate(KeySpec keySpec)
throws InvalidKeySpecException {
if (serviceIterator == null) {
return spi.engineGeneratePrivate(keySpec);
}
Exception failure = null;
KeyFactorySpi mySpi = spi;
do {
try {
return mySpi.engineGeneratePrivate(keySpec);
} catch (Exception e) {
if (failure == null) {
failure = e;
}
mySpi = nextSpi(mySpi);
}
} while (mySpi != null);
if (failure instanceof RuntimeException) {
throw (RuntimeException)failure;
}
if (failure instanceof InvalidKeySpecException) {
throw (InvalidKeySpecException)failure;
}
throw new InvalidKeySpecException
("Could not generate private key", failure);
}
/**
* Returns a specification (key material) of the given key object.
* keySpec identifies the specification class in which
* the key material should be returned. It could, for example, be
* DSAPublicKeySpec.class, to indicate that the
* key material should be returned in an instance of the
* DSAPublicKeySpec class.
*
* @param key the key.
*
* @param keySpec the specification class in which
* the key material should be returned.
*
* @return the underlying key specification (key material) in an instance
* of the requested specification class.
*
* @exception InvalidKeySpecException if the requested key specification is
* inappropriate for the given key, or the given key cannot be processed
* (e.g., the given key has an unrecognized algorithm or format).
*/
public final