Minus one cryptosystem

Minus One Cryptosystem is explained in this paper. Encryption is done by converting every digraph in the plaintext to a single letter. Once the cryptosystem is recognized, frequency analysis is done on the digraphs for decryption. In the usual cryptosystems, if the plaintext is of length k, then the number of possible letter combinations of the ciphertext is 26k. However, an advantage with Minus One Cryptosystem is that the number of possible letter combinations of the ciphertext is only 26k-1. When we apply the encryption m times, we get the string length reduced to n-m. The number m acts as key and can be chosen and exchanged using any convenient Key Exchange Algorithm.