Most applications in areas such as communications, e-commerce and electronic voting are using cryptosystems, to secure their information. So the security evaluation subject can be considered as urgent need to be sure about the security of the used cryptosystems.The security evaluation methods based on the use of basic concepts from two mathematical theories. It employs information theory, which uses entropies related to the cryptosystem, namely H(K), H(K|Y). These entropies are used to compute the amount of revealed key¿s information. Also it employs one of the games in game theory, called diagonal game as a mathematical framework.The method focusses on the security evaluation of more than one cryptosystem. The results are the value of the game (V) and the probabilities of players ¿strategies (p1,p2,p3,q1,q2,q3). These results can be explained from three viewpoints. The first view point concentrates on probabilities of players ¿strategies (p1,p2,p3,q1,q2,q3), which indicate to the security weight of each cryptosystem from the total value (1), which is the sum of the players¿ strategies.