PuTTY (pronounced “putty”) is a popular free SSH client—an application that implements the client side of SSH connections—for Unix and Windows. Its documentation is accessible on the Web.

(a) How does PuTTY handle authentication of a server that it has not previously connected to?

(b) How are clients authenticated to servers?

(c) PuTTY supports several ciphers. How does it determine which one to use for a particular connection?

(d) PuTTY supports ciphers, such as DES, that might be considered too weak for some—or any—situations. Why? How does PuTTY determine which ciphers are weak, and how does it use that information?

(e) For a given connection, PuTTY lets a user specify a maximum amount of time and/or transmitted data after which PuTTY will initiate the establishment of a new session key, which the documentation refers to as a “key exchange” or “rekeying.” What is the motivation behind this feature?

(f ) Use PuTTYgen, the PuTTY key generator, to generate a public–

private key pair for one of the PuTTY-supported public key ciphers.