A key to making cryptography work depends upon how the designer of an encryption system tries to create a scheme for which the best approach to breaking it is through exhaustive search of the key space . The key space must then be large enough to make an exhaustive search completely infeasible. Although the example involves the basic ideas and procedures required for symmetric encryption, any basic encryption process can follow the outline sufficiently. 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 .