Wi-Fi Protected Access

1
Wi-Fi Protected Access

• WPA

2
What is WPA?

• Wi-Fi Protected Access (WPA) is a response by the
  WLAN industry to offer an immediate, a stronger
  security solution than WEP.
• WPA is intended to be
• A software/firmware upgrade to existing access
  points and NICs.
• Inexpensive in terms of time and cost to
  implement.
• Compatible with vendors.
• Suitable for enterprise, small sites, home
  networks.
• Runs in enterprise mode or pre-shared key (PSK)
  mode

3
History of WPA

• WPA was created by the Wi-Fi Alliance, an
  industry trade group, which owns the trademark to
  the Wi-Fi name and certifies devices that carry
  that name.
• WPA is designed for use with an IEEE 802.1X
  authentication server, which distributes
  different keys to each user.

4
History of WPA

• The Wi-Fi Alliance created WPA to enable
  introduction of standard-based secure wireless
  network products prior to the IEEE 802.11i group
  finishing its work.
• The Wi-Fi Alliance at the time already
  anticipated the WPA2 certification based on the
  final draft of the IEEE 802.11i standard.

5
History of WPA

• Data is encrypted using the RC4 stream cipher,
  with a 128-bit key and a 48-bit initialization
  vector (IV).
• One major improvement in WPA over WEP is the
  Temporal Key Integrity Protocol (TKIP), which
  dynamically changes keys as the system is used.
• When combined with the much larger IV, this
  defeats the well-known key recovery attacks on
  WEP.

6
History of WPA

• In addition to authentication and encryption, WPA
  also provides vastly improved payload integrity.
• The cyclic redundancy check (CRC) used in WEP is
  inherently insecure it is possible to alter the
  payload and update the message CRC without
  knowing the WEP key.

7
History of WPA

• A more secure message authentication code
  (usually known as a MAC, but here termed a MIC
  for "Message Integrity Code") is used in WPA, an
  algorithm named "Michael".
• The MIC used in WPA includes a frame counter,
  which prevents replay attacks being executed.

8
History of WPA

• By increasing the size of the keys and IVs,
  reducing the number of packets sent with related
  keys, and adding a secure message verification
  system, WPA makes breaking into a Wireless LAN
  far more difficult.

9
History of WPA

• The Michael algorithm was the strongest that WPA
  designers could come up with that would still
  work with most older network cards.

10
History of WPA

• Due to inevitable weaknesses of Michael, WPA
  includes a special countermeasure mechanism that
  detects an attempt to break TKIP and temporarily
  blocks communications with the attacker.

11
History of WPA

• However, it can also be used in a less secure
  "pre-shared key" (PSK) mode, where every user is
  given the same pass-phrase.

12
History of WPA

• Wi-Fi Protected Access (WPA) had previously been
  introduced by the Wi-Fi Alliance as an
  intermediate solution to WEP insecurities.
• WPA implemented a subset of 802.11i.
• The design of WPA is based on a Draft 3 of the
  IEEE 802.11i standard.

13
WPA Modes

• Pre-Shared Key Mode
• Does not require authentication server.
• Shared Secret is used for authentication to
  access point.
• Enterprise Mode
• Requires an authentication server
• Uses RADIUS protocols for authentication and key
  distribution.
• Centralizes management of user credentials.

14
WPA

• 802.1x
• Features
• BSS
• Key hierarchy
• Key management
• Cipher Authentication Negotiation
• Data Privacy Protocol TKIP

15
Comparing WPA and 802.11i

• 802.1x
• Features
• BSS
• Independent Basic Service Set
• Pre-authentication
• Key hierarchy
• Key management
• Cipher Authentication Negotiation
• Data Privacy Protocols TKIP and CCMP

16
WPA Summary

• Fixes all known WEP privacy vulnerabilities.
• Designed by well-known cryptographers.
• Best possible security to minimize
• performance degradation on existing hardware.

17
Pre-Shared Key Mode Issues

• Needed if there is no authentication server in
  use.
• If shared secret becomes known, network security
  may be compromised.
• No standardized way of changing shared secret.

18
Pre-Shared Key Mode Issues

• Significantly increases the effort required to
  allow passive monitoring and decrypting of
  traffic.
• The more complex the shared secret, the less
  likely it will fall to dictionary attacks.

19
Migration from WEP to WPA

• Existing authentication systems can still be
  used.
• WPA replaces WEP.
• All access points and client will need new
  firmware and drivers.
• Some older NICs and access points may not be
  upgradeable.
• Once enterprise access points are upgraded, home
  units will need to be, if they were using WEP.

20
Migration from WEP to WPA

• Small Office/Home Office
• Configure pre-shared key (PSK) or master password
  on the AP.
• Configure the PSK on client stations.
• Enterprise
• Select EAP types and 802.1X supplicants to be
  supported on stations, APs, and authentication
  servers.
• Select and deploy RADIUS-based authentication
  servers

21
How WPA Addresses the WEP Vulnerabilities

• WPA wraps RC4 cipher engine in four new
  algorithms
• 1. Extended 48-bit IV and IV Sequencing Rules
• 248 is a large number! More than 500 trillion
• Sequencing rules specify how IVs are selected and
  verified
• 2. A Message Integrity Code (MIC) called Michael
• Designed for deployed hardware
• Requires use of active countermeasures
• 3. Key Derivation and Distribution
• Initial random number exchanges defeat
  man-in-the-middle attacks
• 4. Temporal Key Integrity Protocol generates
  per-packet keys

22
Wi-Fi Protected Access 2 WPA2

• Uses the Advanced Encryption Standard (AES)
• AES selected by National Institute of Standards
  and Technology (NIST) as replacement for DES.
• Symmetric-key block cipher using 128-bit keys.
• Generates CCM Protocol (CCMP)
• CCMP CTR CBC MAC
• CTR Counter Mode Encryption
• CBC/MAC Cipher Block Chaining/Message
  Authentication Code

23
Encryption Method Comparison

• WEP
  WPA WPA2
• Cipher RC4 128
  bits encrytion AES
• Key Size 40 bits 64 bits
  authentication 128 bits
• Key Life 24 bits IV
  24 bits IV 24 bits IV
• Packet Key concatened Mixing
  Function Not Nedeed
• Data Integrity CRC-32
  Michael CCMP
• Header Integrity none
  Michael CCMP
• Replay Attack none IV
  sequence IV sequence
• Management Key none
  EAP-based EAP-based

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General Recommendations

• Conduct a risk assessment for all information
  that will travel over the WLAN and restrict
  sensitive information.
• Policies and infrastructure for authenticating
  remote access users can be applied to WLAN users.
• Perform regular audits of the WLAN using network
  management and RF detection tools.

25
General Recommendations

• Minimize signal leakage through directional
  antennas and placement of access points.
• Make sure all equipment being purchased can be
  upgraded to support WPA and WPA 2/AES.
• If using Pre-Shared Key Mode consider that the
  shared secret may become compromised.

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Should you upgrade to WPA2 with AES after WPA?

• An investment in new hardware (access points,
  NICs) may be needed.
• Does your risk analysis indicate the extra
  protection ?
• Is there a compelling business reason to do so?

27
Should you upgrade to WPA2 with AES after WPA?

• However
• WPA has not met the challenge of intensive
  traffic.WPA has some vulnerabilities

28
WPA Vulnerabilties

• Uso de senhas pequenas ou de fácil advinhação.
• Está sujeito a ataques de força bruta (quando o
  atacante testa senhas em sequência) ou ataques de
  dicionário (quando o atacante testa palavras
  comuns - dicionário).

29
WPA Vulnerabilties

• Senhas de menos de 20 caracteres são mais
  susceptíveis à ataque de força bruta.
• É comum o fabricante deixar senhas de 8-10
  caracters, imaginando que o administrador irá
  alterá-las.

30
WPA Vulnerabilties

• Existem ferramentas disponíveis que promovem
  ataques de força bruta e/ou dicionário para
  ataques ao WPA.
• KisMAC para MacOS X (força bruta para
  senhas/dicionário).
• WPA Crack para Linux (força bruta para
  senhas/dicionário).
• Ethereal para
• Cowpatty para Linux (dicionário) ou combinadas
  com John the Ripper.

31
WPA Vulnerabilities

• Não há dificuldades em modificar programas de
  acesso ao WPA.
• Como por exemplo, em WPA_supplicant) para
  permitir a descoberta de chave pré-compartilhada
  (PSK) ou do TKIP que muda a chave de tempos em
  tempos de forma configurável.

32
WPA Vulnerabilities

• O arquivo config.c pode ser modificado na função
  wpa_config_psk, para ao invés de ler a chave no
  arquivo de configuração, passa a ler palavras
  recebidas como parâmetros, permitindo o uso de
  dicionário e mais algum programa para quebra de
  senha, como John The Ripper.

33
WPA Vulnerabilities

• Problemas no armazenamento das chaves, tanto nos
  clientes como nos concentradores, que podem
  comprometer a segurança.

34
How WPA Addresses the WEP Vulnerabilities

• WPA wraps RC4 cipher engine in four new
  algorithms
• 1. Extended 48-bit IV and IV Sequencing Rules
• 248 is a large number! More than 500 trillion
• Sequencing rules specify how IVs are selected and
  verified
• 2. A Message Integrity Code (MIC) called Michael
• Designed for deployed hardware
• Requires use of active countermeasures
• 3. Key Derivation and Distribution
• Initial random number exchanges defeat
  man-in-the-middle attacks
• 4. Temporal Key Integrity Protocol generates
  per-packet keys

35
Referências

• KisMAChttp//binaervarianz.de/programmieren/kisma
  c
• Cowpattyhttp//www.remote-exploit.org/?pagecodes
  
• WPA_attack
• http//www.tinypeap.com/page8.html
• WPA_Supplicant
• http//hostap.epitest.fi/wpa_supplicant

36
Conclusions on WEP and WPA

• WEP is insufficient to protect WLANs today from
  determined attackers.
• WPA resolves all of WEPs known weaknesses.
• WPA is a dramatic improvement in Wi-Fi security.

37
Conclusions on WEP and WPA

• WPA provides an enterprise-class security
  solution for user authentication and encryption.
• WPA is a subset of the 802.11i draft standard and
  is expected to maintain forward compatibility
  with the standard.

38
Conclusions on WEP and WPA

• WPA2 will provide an even stronger cryptographic
  cipher than WPA.

39
Conclusions on WEP and WPA

• Unless there is a significant flaw found in WPA
  or RC4 is broken, there may be no reason to move
  to WPA2 in the future.