Basic Wireless LAN Security Technologies

1
Basic Wireless LAN Security Technologies

• Most wireless security incidents occur because
  system administrators do not implement available
  counter measures.
• It is important to verify that the countermeasure
  is in place and working properly
• Thus, WLAN security wheel which is a continuous
  security process is very effective

2
WLAN Security Wheel

• The Four Steps of Wireless Security Policy
• Secure
• Monitor
• Test
• Improve

3
Secure

• This step implements WLAN security solutions to
  stop or prevent unauthorized access or activities
  and to protect information using the following
• Authentication (802.1x)
• Encryption (WEP or AES)
• Traffic Filters
• Controlled wireless coverage area

4
Monitor

• This step involves the following actions
• Detecting violations to the WLAN security policy
• Involving system auditing, logs, and real-time
  intrusion detection
• Validating the security implementation in step 1

5
Test Improve

• Test This step validates the effectiveness of
  the WLAN security policy through system auditing
  and wireless and wired vulnerability scanning
• Improve This step involves the following
• Using info from step 3 to improve WLAN
  implementation
• Adjusting the security policy

6
First Generation Wireless Security

• Security was not a big concern
• Many WLANs used Service Set IDentifier (SSID) as
  the basic form of security.
• Some WLANs controlled access by entering the MAC
  address of each client into their wireless AP.
• Neither option was secure, because wireless
  sniffing could reveal both valid MAC addresses
  and the SSID

7
SSID

• SSID is a 1-32 character ASCII string that can be
  entered on the clients and APs
• In 802.11, any client with a NULL string
  associates to any AP regardless of SSID setting
  on an AP
• Broadcast SSIDs are required by the IEEE
  standard.
• Some vendors have options such as SSID broadcast
  and allow any SSID

8
SSID

• These features are enabled by default and make it
  easy to set up a wireless network
• Using the allow any SSID option lets the AP allow
  access to a client with blank SSID
• The SSID broadcast option sends beacon frames
  which advertise the SSID
• MAC based authentication is not defined in 802.11
  specification

9
Wired Equivalent Privacy (WEP)

• IEEE 802.11 standard includes WEP to protect
  authorized users of a WLAN from a casual
  eavesdropping
• IEEE 802.11 WEP standard specifies a static
  40-bit key
• Most vendors have extended WEP to 128 bits or
  more.
• When using WEP, both AP and wireless client must
  have a matching WEP key
• WEP is based on Rivest Cipher 4 (RC4)

10
WEP

• Encryption based on key lengths greater than 64
  bits are considered high encryption standard

11
Rivest-Shamir-Adelman (RSA) Encryption Scheme

• In RSA scheme messages are first represented as
  integers in the range (0,n-1)
• Each user chooses his/her own value of n and
  another pair of positive integers e and d.
• The user places the encryption key, (n,e) in the
  public directory
• The decryption key consists of the number pair
  (n,d)

12
RSA Scheme

• d is kept secret.
• Encryption
• Decryption

13
RSA Scheme

• n is obtained by selecting two large prime
  numbers p and q such that npq
• Although n is made public, p and q are kept
  secret due to the great difficulty in factoring n
• Then the Euler totient function is formed. That
  is,

14
RSA Scheme

• The parameter has an interesting property
  that for any integer X in the range (0, n-1) and
  for any integer k
• A large integer d is randomly chosen so that it
  is relatively prime to , which means that
  and d must have no common divisors other
  than 1

15
RSA Scheme

• That is gcd ,d1
• Any prime number greater than the larger of
  (p,q) will suffice. Then the integer e, where
  0ltelt , is found from the relationship
• which amounts to choosing e and d to satisfy
  Thus,

16
Example of RSA Scheme

• Let p47, q59. Therefore, npq2773
• (p-1)(q-1)2668. d is chosen to be
  relatively prime to . For example, choose
  d157. Next the value of e is computed as
  follows
• Thus e17

17
RSA Scheme

• Consider ITS ALL GREEK TO ME
• Replacing each letter with a two-digit number in
  the range (01, 26) encoding blank as 00
• 0920 1900 0112 1200 0718 0505 1100 2015 0013 0500
• Each message needs to be expressed as an integer
  in the range (0, n-1) For this example,
  encryption is done on blocks of 4 digits at a
  time since this is the maximum number of digits
  that will always yield a number less than
  n-12772

18
RSA Scheme

• The first 4 digits (0920) of the plaintext are
  encrypted as
• C0948 2342 1084 1444 2663 2390 0778 0774 0219
  1655