On Wed, Jul 26, 2000 at 11:53:07PM -0700, James A. Donald wrote:
> Looking at someone's face, and hearing his voice, is good enough in
> all common circumstances, and common circumstances means "where the
> customers are".
Someone can pull off a man-in-the-middle attack without having to "put
on make up, [and] declare himself to be the other person". I think MITM
could be done effectively against your protocol without requiring
special help from the server. Some trivial misdirection is all that is
required...
Suppose you have a server with a user list like this:
ID Owner
----------------------
Alice The Real Alice
Bob The Real Bob
Alice' Mallory
Bob' Mallory
Mallory sends The Real Alice an email claiming to be from The Real Bob
(this can be done with the usual spoofing), telling Alice that she can
contact "him" as "Bob'". Later, Alice has something important to
discuss with Bob, so she asks the server for credentials for "Bob'".
You can probably guess the rest, but here it is anyway:
(Honest Server)
/ |
/ |
/ (Mallory)
Alice <--> Bob'
Now Mallory as Alice' establishes a connection to Bob:
(Honest Server)
| \
| \
(---Mallory---) \
Alice <--> Bob' / Alice' <--> Bob
Mallory silently forwards between Bob' and Alice'. The end result is
that The Real Alice is talking to The Real Bob and vice versa.
Meanwhile, Mallory calls up Eve: "Bring popcorn."
This might be classified as a user interface problem. But as you said,
"Looking at someone's face, and hearing his voice, is good enough in
all common circumstances". That's why this attack will work. When Alice
sees Bob's face and hears his voice, any questions she had about that
little apostrophe at the end of his user ID will disappear. When you
call someone on the phone, and get the right person, you stop wondering
if you dialed the wrong number.
