Keystore implementations are provider-based, which means the application interfaces supplied by the KeyStore class are implemented in terms of a Service Provider Interface (SPI). There is a corresponding abstract KeystoreSpi class, also in the java.security package, that defines the Service Provider Interface methods that providers must implement. The term provider refers to a package or a set of packages that supply a concrete implementation of a subset of services that can be accessed by the Java Security API. To provide a keystore implementation, clients must implement a provider and supply a KeystoreSpi subclass implementation, as described in How to Implement a Provider in the Java Cryptography Architecture at