The Security on web is essential. The semantic security provides confidentiality. Many methods are used in order to guarantee the security of information and to preserve intrusions. The cryptography is one of domains , which takes care this security. In the cryptography, it exists different methods among them the cryptography with the Vigenere matrix. Our article presents a system of cryptanalysis permitting the data transfer of an application client/server banking in secure manner. A net banking application is presented. So we propose to use θ - Vigenere cipher at character level by the Syverson's protocol to assure confidentiality, integrity, no repudiation and authentication. This protocol is based on game theory uses a random key. It also uses digital signature for authentication. © 2005 IEEE.