> IP Switches and Routers

IP Switches and Routers
Although their position is defined by a standard data network rather than VoIP, a
router’s purpose in life is to connect two or more IP subnetworks at layer 3. An IP
switch performs a similar function at layer 2. Routers and switches operate on the
network and data-link layers, respectively, investigating the IP address or MAC
address for each packet to determine its final destination and then forwarding that
packet to its recipient. For VoIP, the biggest consideration at these levels are QoS
markings and treatment such as DiffServ and RSVP, which should be supported by
this infrastructure in a way that allows legitimate voice packets through with high
priority and shuts out malicious packets, particularly those aimed at causing DoS
attacks.This may be easier said than done in some cases. If an attacker can inject
QoS-marked packets into your network, will your QoS scheme create a DoS condition
for both voice and data?



Wireless Infrastructure
Wireless access points and associated infrastructure are similarly considered an extension
of the data network. However, the increasing use of VoIP clients within this
infrastructure creates several unique security considerations (particularly DoS given
that wireless is a shared medium). In addition, wireless VoIP devices in the marketplace
have lagged in implementation of the most current wireless encryption recommendations.
All this should be taken into consideration in the design and operation
of wireless VoIP.


Wireless Encryption:WEP
When wireless networking was first designed, its primary focus was ease of implementation,
and certainly not security. As any security expert will tell you, it’s
extremely difficult to secure a system after the fact.WEP, the Wired Equivalent
Privacy encryption scheme, initially was targeted at preventing theft-of-service and
eavesdropping attacks. WEP comes in two major varieties, standard 64-bit and 128-
bit encryption. 256-bit and 512-bit implementations exist, but they are not nearly as
supported by most vendors. 64-bit WEP uses a 24-bit initialization vector that is
added to the 40-bit key itself; combined, they form an RC4 key. 128-bit WEP uses a
104-bit key, added to the 24 bit initialization vector. 128-bit WEP was implemented
by vendors once a U.S. government restriction limiting cryptographic technology
was lifted.
In August of 2001, Fluhrer, Mantin, and Shamir released a paper dissecting cryptographic
weaknesses in WEP’s RC4 algorithm.They had discovered that WEP’s 24-bit
initialization vectors were not long enough, and repetition in the cipher text existed
on busy networks.These so-called weak IVs leaked information about the private key.
An attacker monitoring encrypted traffic long enough was able to recreate the private
key, provided enough packets were gathered. Access Point Vendors responded by
releasing hardware that filtered out the weak IVs.
However, in 2004 a hacker named Korek released a new statistical-analysis attack
on WEP, which led the way to a whole new series of tools.These new wireless
weapons broke WEP using merely IVs, and no longer just IVs were considered
weak. On a 64-bit WEP encrypted network, an attacker need gather only around
100,000 IVs to crack in (although more certainly increases the chance of penetration)
and only 500,000 to 700,000 for 128-bit WEP. On a home network, it can
take days, even weeks to see enough traffic to make cracking the key possible.
However, clever attackers discovered a way to stimulate network traffic by replaying
encrypted network level packets at the target. By mimicking legitimate network
traffic, the target network would respond over and over, causing a flood of network
traffic and creating IVs at an accelerated rate.With this new attack, a 128-bit WEP
network can be broken in as little as 10 minutes.



Wireless Encryption:WPA2
WPA,WiFi Protected Access, was created to address overwhelming concerns with
WEP’s inadequacy.WPA uses RC4; however, it uses a 128-bit key appended to a 48-
bit initialization vector.This longer key defeats the key recovery attacks made popular
against WEP using the Temporal Key Integrity Protocol (TKIP), which changes keys
mid-session, on the fly. Additionally, the Message Integrity Code (MIC) includes a
frame counter in the packet, which prevents the replay attacks that cripple WEP.
WPA2 was the child of the IEEE group, their certified form of 802.11i. RC4
was replaced by the favorable AES encryption scheme, which is still considered
secure.WPA’s MIC is replaced by CCMP, the Counter Mode with Cipher Block
Chaining Message Authentication Code Protocol. CCMP checks to see if the MIC
sum has been altered, and if it has, will not allow the message through.
Perhaps the most beneficial attribute of WPA2 is its ease of implementation. In
most cases, hardware vendors needed only reflash the firmware of their Access Points
to allow for WPA2 compatibility.
Although considerably stronger than its older brother,WEP,WPA2 is not without
guilt.WPA2 encrypted traffic is still susceptible to dictionary attacks since WPA2 uses
a hashing algorithm that can be reproduced. Joshua Wright released a tool called
coWPAtty, which is a brute-force cracking tool that takes a list of dictionary words
and encrypts them using WPA2s algorithms, one at a time.The encrypted value of
each word then is compared against the encrypted value of captured traffic, and if the
right password is found, POOF! The packet becomes intelligible.
Although brute-force cracking is not guaranteed to yield results, it leverages a
weakness found in almost all security mechanisms—the user. If a user chooses a password
that is not strong enough, or uses semipredictable modifications (the use of the
number 3 instead of “e”), the network will fall. It is recommended that users install a
pass-phrase instead of a traditional password. A pass-phrase longer than eight characters,
which includes nonalphanumeric characters, is much less likely to be discovered
by brute-forcing methods. And never, ever, use a dictionary word as a password, as
these will often be discovered within minutes using freely available software from the
Internet.
When implementing wireless VoIP, always use WPA2 or use an alternative means
for protecting the VoIP stream (i.e., media and signaling encryption or IPSEC tunneling).
Given the speed with which WEP can be cracked, it’s almost pointless to use
it since it adds encryption latency and creates a false sense of security.