The KeyFactory Class

The KeyFactory class is an engine class designed to provide conversions between opaque cryptographic keys (of type Key) and key specifications (transparent representations of the underlying key material).

Key factories are bidirectional. 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 can exist for the same key. For example, a DSA public key can be specified by its components y, p, q, and g (see DSAPublicKeySpec), or it can be specified using its DER encoding according to the X.509 standard (see X509EncodedKeySpec).

A key factory can be used to translate between compatible key specifications. Key parsing can be achieved through translation between compatible key specifications, for example, when you translate from X509EncodedKeySpec to DSAPublicKeySpec, you basically parse the encoded key into its components. For an example, see the end of the Generating/Verifying Signatures Using Key Specifications and KeyFactory section.

Creating a KeyFactory Object

As with all engine classes, the way to get a KeyFactory object for a particular type of key algorithm is to call the getInstance static factory method on the KeyFactory class:

static KeyFactory getInstance(String algorithm)

Note: The algorithm name is not case-sensitive.

A caller can optionally specify the name of a provider or the Provider class, which will guarantee that the implementation of the key factory requested is from the named provider.

static KeyFactory getInstance(String algorithm, String provider)
static KeyFactory getInstance(String algorithm, Provider provider)

Converting between a Key Specification and a Key Object

If you have a key specification for a public key, you can obtain an opaque PublicKey object from the specification by using the generatePublic method:

PublicKey generatePublic(KeySpec keySpec)

Similarly, if you have a key specification for a private key, you can obtain an opaque PrivateKey object from the specification by using the generatePrivate method:

PrivateKey generatePrivate(KeySpec keySpec)

Converting between a Key Object and a Key Specification

If you have a Key object, you can get a corresponding key specification object by calling the getKeySpec method:

KeySpec getKeySpec(Key key, Class keySpec)

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.

See the Examples section for more details.