Java Cryptography

Getting Started

Algorithm Names and Implementations

A cryptographic provider is a set of classes that implement cryptographic algorithms. A Provider subclass keeps track of how the algorithm names and classes are related. Basically, it’s a list of algorithm names and their corresponding implementations. For example, in Chapter 7, we developed the CBCWrapper class, which (by default) supports DES in CBC mode with PKCS#5 padding. We also developed the CFBWrapper class, which supports DES in eight-bit CFB mode with no padding. A simple provider then might map algorithm names to class names like this:

DES/CBC/PKCS5Padding : oreilly.jonathan.crypto.CBCWrapper
DES/CFB/NoPadding : oreilly.jonathan.crypto.CFBWrapper

Remember, though, that a cryptographic provider can include several different kinds of algorithms: key pair generation, signatures, ciphers, and others. How does the provider know which is which? The algorithm name is actually made up of a type and a name, as follows:

Cipher.DES/CBC/PKCS5Padding : oreilly.jonathan.crypto.CBCWrapper
Cipher.DES/CFB/NoPadding : oreilly.jonathan.crypto.CFBWrapper

The type corresponds to a cryptographic concept class, like Cipher or Signature. The implementation class is the corresponding SPI class, like javax.crypto.CipherSpi or java.security.SignatureSpi. Later, for example, we’ll develop a class that implements the ElGamal signature algorithm. It’s a subclass of SignatureSpi. To associate the algorithm name and the implementation class, our provider ...