Applications and the Future - Codes: The Guide to Secrecy from Ancient to Modern Times - page 332

and Bob are communicatingover an Ethernet channel with a packet sniffer
attached, Mallory can read all the traLc between them. Packet sniffers on an
Ethernet consist of the followingcomponents.
Packet Sniffer Components
1. Hardware : In promiscuous mode, every packet is received and read by a
network adapter , which is a physical device such as a card (and its software
driver) that connects a host computer to network traLc, allowingthe host
to send and receive packets. A network adapter is sometimes called a
network interface .
2. Capture Driver : This type of driver captures the network traLc and
stores it to a buffer, for instance. A driver in general, is a program that
controls a particular device, such as a printer, or disk drive. Either the
driver will come with the operatingsystem or have to be loaded when the
device is added. Think of a driver as a translator between the device and
the programs using the device.
A device driver is a program that controls a specific device such as a
printer. Thus, we may (informally) think of a capture driver as a program
that controls the capture of information packets for the packet sniffer.
3. Buffer : The captured data from the network are stored in a buffer until
they can be analyzed.
4. Protocol Analyzer : This aspect of the packet sniffer strips off any encod-
ingand analyzes the data (see Section D.6 on page 541).
The antithesis of promiscuous mode is nonpromiscuous mode wherein pack-
ets are scanned and passed on if those data packets are not theirs. Only the
target site device receives and reads the data in this mode.
Now we return to the issue of login security. We have addressed the issue
of password selection and checking, remote logins, and attacks that may obtain
passwords. We turn to a modern secure method for password storage.
Security Tokens
A security token is a special device (a physical object usually ranging in size
from that of a housekey to that of a credit card), which a user carries for the
purpose of authorized access to a network. For example, the device may be
embedded in a key fob , which has the physical appearance of a key, but has
built-in authentication mechanisms consistingof the following:
1. The user's PIN, authenticating, say Alice, as the fob's owner.
2. A login ID, which is displayed after Alice correctly enters her PIN, allowing
her to login to the network.