SSHv1 and PuTTY

One of the advantages of writing books is that you must double-check everything you thought you knew about a topic. PuTTY is probably the most widely deployed SSH client in the world. I've used it for years. It's good software. (I also use the OpenSSH client, of course.)

To my surprise, PuTTY accepts both version 1 and 2 of the SSH protocol. It prefers version 2, but will accept 1.

Version 1 of the SSH protocol has irremediable problems. If a client accepts SSHv1, an attacker can intercept a...