This paper presents a survey of proof by knowledge authentication techniques (text passwords, visual passwords and graphical passwords). Both new methods are more memorable, as people have to remember images and not characters and graphical passwords are also more secure. A total of 100 users participated in our survey, who after getting informed about the new authentication methods, they answered the questions of our questionnaire. Based on their answers, all participants have many passwords for their everyday needs and they try to select passwords that are not only memorable, but also secure. Unfortunately, they can not deal with proper password selection and they become victims of dictionary attacks. Understanding this situation, participants were very positive in learning more about the new authentication methods. They found both techniques memorable and friendly – visual passwords at most. However, they found graphical passwords a bit more complex and difficult to learn how to use them, something that they can overcome with small practice.

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This paper presents an electronic cash scheme using the theory of continued fractions. Continued fractions have already some utilities in cryptography such as in the cryptanalysis of RSA [17] or in the design of some stream ciphers [9]. In order to achieve our prepaid e-cash scheme, we will use the continued fraction expansion of some irrationals numbers, although the same scheme can be obtain with a block cipher algorithm like AES or with some pseudo-random generators. Our e-cash scheme has two aims: the first one is to create a payment system independent of current constraints such as the revocation of anonymity (in the double spending case) or the obligation for those who want to use the e-cash, to have a bank account. The second aim is to propose here a solution which prevents the copy of our e-coins and allows if necessary the reimbursement of the user with e-cash.

The Diffie-Hellman key algorithm was the first proposed public key algorithm by which two parties can communicate with each other without having any prior knowledge of each other over an insecure communication channel proposed by Harn.et.al. Diffie-Hellman key exchange algorithm is the most famous algorithm to exchange keys over a network but it has some false and drawbacks. So in our work we have proposed a new agreement protocol based on key confirmation as well as Diffie-Hellman algorithm. This protocol also works on the elliptic curve cryptography in asymmetric encryption.