Architectural defects of the secure shell

Although flaws have been found out in SSH, the Secure Shell, there has been little discussion about its architecture or design safety. Therefore, considering SSH architecture, e.g. the key exchange protocol, user authentication protocols and total design of the SSH, we not only discuss SSH architectural safety but show critical flaws for SSH users. For establishing the SSH connection, before user authentication, the SSH server and client exchange a session key, which can communicate securely. Then, over the secret channel encrypted by the session key, the SSH server authenticates a user in the SSH client using a user´s password or public key. However, owing to defects in the SSH protocols and its design, a user can be deprived of their password in the authentication protocol. Moreover, we show that those who use its public key for authentication are exposed to the same risks as password-oriented users.