Symmetric Encryption
In Chapter 3 we introduced symmetric encryption, and in this chapter we're going to elaborate on the
subject by describing how to use the JCE to perform symmetric encryption. To begin with, we will look at
how we encrypt and decrypt using symmetric encryption. Then we discuss applications for symmetric
encryption, followed by some examples, which deal with the following aspects of encryption:
- Basic encryption
- Encryption using Blowfish
- Password-based encryption
The main topics discussed in this chapter are:
- Key storage, including wrapping and unwrapping
- Modes
- Cipher streams and how to initialize ciphers with an initialization vector
- Sealed objects
Remember, before trying to run any of the code in the chapter you'll need an encryption engine
installed. Here we'll be using the Bouncy Castle provider because it has support for many
algorithms, and won't restrict us from using any other providers in the future (instructions for its
installation are provided in the previous chapter).
Encryption and Decryption
Symmetric encryption, also known as secret-key encryption, is the simplest type of encryption. A single key
is used, which must be kept secret, hence the name. In order to encrypt data, we take the key and use it to
initialize a cipher. The cipher can then be used to encrypt data passed to it. Decryption is similar – a cipher
gets initialized with the same key, and the data passed in is decrypted.
The strength of encryption is based on the length of the key. For symmetric encryption, that key length is
typically between 40 and 128 bits, but some algorithms can have even longer keys. DES, which is probably
the most commonly used symmetric algorithm, has a key length of 56 bits, which is really not enough for a
secure system, as we discussed in Chapter 3. We should use at least 128 bit keys if we're going to use
symmetric encryption.
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