ICS 351: Today's plan

ISM bands

to operate most radios, a license is needed from a government body (in the U.S., the FCC)
to operate a microwave oven, no license is needed
microwave ovens work on the resonant frequency of water, 2.4GHz
the 2.4GHz-2.5GHz band has been designated an Industrial, Scientific, and Medical (ISM) band, free to use worldwide without a license (as long as transmission power is limited -- and some countries restrict part of this band)
ISM equipment needs to tolerate interference (e.g., from microwave ovens!)
there are many ISM bands, but most are limited to only some countries
due to the unprecedented availability of the 2.4GHz band, many applications have been developed for it

an early marketing term for 802.11 was WiFi (a pun on HiFi)
802.11 works mostly in the 2.4GHz band, though 802.11a works in the 5GHz band
many successive standards, 802.11 (1-2Mb/s), 802.11a (54Mb/s), 802.11b (11Mb/s), 802.11g (54Mb/s) and foreseeable future versions
two modes: ad-hoc (point-to-point) and managed
in managed mode, all communication is to or from a central access point
end-nodes contend for the medium: this contention may result in collisions that require retransmissions

tapping a wired network requires physical access to the wires
tapping a wireless network requires being in range of the signal
originally, cryptographic Wired Equivalent Privacy (WEP) was introduced to hide the contents of the messages
the original design for WEP was not widely published -- unfortunately, this lead to a lack of serious examination of the protocol (security by obscurity often does not work)
unfortunately, WEP is sufficiently weak that it can be cracked by listening to a few minutes of busy traffic
802.11i introduced:
- WiFi Protected Access (WPA), a simple but much stronger encryption protocol, and
- WPA2, stronger than WPA and requiring more resources for implementation (including, in some cases, newer equipment)

"in the clear" protocol can be easily broken when information is snooped: telnet, ftp, http, many email protocols
encrypted protocol are secure against many attacks, including someone examining the data: ssh/scp, https, secure POP/IMAP, PGP
most protocols are not secure against traffic analysis
some general principles:
- it is usually better to have more security than less security
- security that inconveniences users is more likely to be resisted or circumvented
- security can inadvertently lock out people who should have access
- data requiring security should not be sent unencrypted over the Internet (because some of the links may be accessible to adversaries)
- data requiring security is still often sent unencrypted over the Internet (but data with monetary value is usually protected these days)
host security is more concerned with installing applications, running foreign code, firewalls/NATs, etc

using the ad-hoc mode of 802.11, any machine ("node") may directly talk to any other node
if nodes agree to forward data for each other, they can form a wireless ad-hoc network
machines may move or go to sleep, so routing can be challenging
also, the notion of a "link" is different for wired and wireless networks: successful wireless protocols take advantage of broadcasting
generally machines should discover each other and automatically send data to the destination
a wireless mesh network consists of static wireless nodes
possibly with some wired nodes coordinating to provide Internet access
mobile nodes may obtain Internet access from nodes in a mesh network