This module exposes the low-level internal details of ciphers. Do not import this module unless you want to implement a new cipher or give a new implementation of an existing cipher.

Ciphers provide symmetric encryption in the raaz library and are captured by the type class Cipher. They are instances of the class Symmetric and the associated type Key captures the all that is required to determine the encryption and decryption process. In most ciphers, this includes what is know as the _encryption key_ as well as the _initialisation vector_.

Instances of Cipher is only required to provide full block encryption/decryption algorithms. Implementations are captured by two types.

CipherI:

Values of this type that captures implementations of a cipher. This type is parameterised over the memory element that is used internally by the implementation.

SomeCipherI:

The existentially quantified version of CipherI over its memory element. By wrapping the memory element inside the existential quantifier, values of this type exposes only the interface and not the internals of the implementation. The Implementation associated type of a cipher is the type SomeCipherI

To support a new cipher, a developer needs to:

1. Define a new type which captures the cipher. This type should be an instance of the class Cipher.
2. Define an implementation, i.e. a value of the type SomeCipherI.
3. Define a recommended implementation, i.e. an instance of the type class Recommendation

Stream ciphers are special class of ciphers which can encrypt messages of any length (not necessarily multiples of block length). Typically, stream ciphers are obtained by xoring the data with a stream of prg values that the stream ciphers generate. As a consequence, the encryption and decryption is the same algorithm. one can also use the stream cipher as a pseudo-random generator.

We have the class StreamCipher that captures valid stream ciphers.

We expose some unsafe functions to encrypt and decrypt bytestrings. These function works correctly only if the input byte string has a length which is a multiple of the block size of the cipher and hence are unsafe to use as general methods of encryption and decryption of data. Use these functions for testing and benchmarking and nothing else.

There are multiple ways to handle arbitrary sized strings like padding, cipher block stealing etc. They are not exposed here though.