To begin, some common terminology will need to be applied in order to set up the example. A denotes a finite set called the alphabet of definition . C denotes a set called the ciphertext space . C consists of strings of symbols from an alphabet of definition, which may differ from that of M . An element of C is called ciphertext .
D denotes a decryption function or decryption transformation .
Each element d of K determines a bijection from C to M . E denotes an encryption function or encryption transformation . Each element e of K determines a bijection from M to C . K denotes a set called the key space . An element of K is called a key .