Problem:

(a) What is the minimum length of a password that could be considered to be "strong" in the context of today's computing power?

(b) The security of a PIN system, as used in auto teller machines, is actually higher than it might at first seem. Why?

(c) With the aid of diagrams, explain how public-key encryption systems may be used to simultaneously provide both confidentiality and authentication of messages between two users who neither know nor trust each other.

(d) In a public key cryptosystem based on RSA technology, explain briefly what aspect of the system makes it difficult to discover someone else's private key Kp even though you know their public key Ku.

(e) One of the major disadvantages of a public key cryptosystem based on RSA is its slow speed of encryption and decryption. Explain briefly why the RSA algorithm is slow compared to a single-key encryption system such as DES. How can public key and single key encryption be combined to give a secure, but fast, encryption system?

(f) Active X controls are digitally signed. Why doesn't a digital signature mean that an ActiveX control is secure?