Weak keys of graph cryptography

This paper presents two families of weak keys, which can be combined to build a family of very weak keys. The detection algorithm of weak keys is introduced. Graph cryptography relics on the fact that a path in a directed graph can he expressed using the vertices or the edges. The main idea is to represent the encryption of any symbol with Markov chains. This is possible because the encryption of each symbol only depends on the previous encrypted symbol. Experimental results show that the key should always be tested to detect if it is an absorbing key, and if any absorbing sub key is a polyalphabetic substitution key.