Java in a Nutshell, 5th Edition [Electronic resources]

This class translates asymmetric cryptographic keys between the two representations used by the Java Security API. java.security.Key is the opaque, algorithm-independent representation of a key used by most of the Security API. java.security.spec.KeySpec is a marker interface implemented by transparent, algorithm-specific representations of keys. KeyFactory is used with public and private keys; see javax.crypto.SecretKeyFactory if you are working with symmetric or secret keys.

To convert a Key to a KeySpec or vice versa, create a KeyFactory by calling one of the static getInstance( ) factory methods specifying the name of the key algorithm (e.g., DSA or RSA) and optionally specifying the name or Provider object for the desired provider. Then, use generatePublic( ) or generatePrivate( ) to create a PublicKey or PrivateKey object from a corresponding KeySpec. Or use getKeySpec( ) to obtain a KeySpec for a given Key. Because there can be more than one KeySpec implementation used by a particular cryptographic algorithm, you must also specify the Class of the KeySpec you desire.

If you do not need to transport keys portably between applications and/or systems, you can use a KeyStore to store and retrieve keys and certificates, avoiding KeySpec and KeyFactory altogether.

public class 
KeyFactory  {
// Protected Constructors
protected 
KeyFactory (KeyFactorySpi 
keyFacSpi , Provider 
provider , 
String 
algorithm );  
// Public Class Methods
public static KeyFactory 
getInstance (String 
algorithm ) 
throws NoSuchAlgorithmException;  
public static KeyFactory 
getInstance (String 
algorithm , String 
provider ) 
throws NoSuchAlgorithmException, NoSuchProviderException;  
1.4   public static KeyFactory 
getInstance (String 
algorithm , Provider 
provider ) 
throws NoSuchAlgorithmException;  
// Public Instance Methods
public final PrivateKey 
generatePrivate (java.security.spec.KeySpec 
keySpec ) 
throws java.security.spec.InvalidKeySpecException;  
public final PublicKey 
generatePublic (java.security.spec.KeySpec 
keySpec ) 
throws java.security.spec.InvalidKeySpecException;  
public final String 
getAlgorithm ( );  
public final <T extends java.security.spec.KeySpec> T 
getKeySpec (Key 
key , 
Class<T> 
keySpec ) 
throws java.security.spec.InvalidKeySpecException;  
public final Provider 
getProvider ( );  
public final Key 
translateKey (Key 
key ) throws InvalidKeyException;  
}