Wi-Fi Protected Access ( WPA and WPA2 ) is a mechanism to make safe the network X wireless telegraphy of the type Wi-Fi. They were created in answer to the many ones and severe weaknesses that researchers found in the preceding mechanism, WEP. WPA respects the majority of the standard IEEE 802.11i and was envisaged as an intermediate solution to replace the WEP while waiting for that the standard 802.11i is finished. WPA was conceived to function, after update of their microsoftware, with all the charts Wi-Fi, but not necessarily with the first generation of the access points Wi-Fi. WPA2 as for him respects the whole standard, but cannot be implemented on the old materials. The two mechanisms provide a good safety, if two important points are respected:

• the user must still often make the explicit choice activate WPA or WPA2 to replace the WEP, because the WEP remains usually the choice of coding per defect on the majority of the equipment.
• when the mode Personal (the most probable choice for the individual ones and SME) is used, a secret Phrase longer than traditional the passwords from 6 to 8 characters used by the users is necessary to ensure a complete safety.

History

WPA was created by the Wi-Fi Alliance, an association of companies, which has the rights on the initials Wi-Fi and which certify the bearing material these initials. Certifications of the establishments of the WPA began in April 2003 and became obligatory in November 2003. The standard 802.11i supplements was ratified in June 2004.

WPA was conceived to be used in collaboration with a waiter of identification 802.1X charged to distribute the various keys to each user. However, it can also be used in a protected mode, called pre-shared key (PSK), in which all the users share the same secret sentence. Wi-Fi Alliance indicates the version pre-shared key , WPA-Personal or WPA2-Personal and the version with identification 802.1X WPA-Enterprise or WPA2-Enterprise .

The data are quantified by using the algorithm of Chiffrement by flood RC4, with a key of 128 bits and a Vecteur of initialization ( initialization vector or IV in English) of 48 bits. One of the major improvements of the WPA compared to WEP is the protocol Temporal Key Integrity Protocol (TKIP), which exchanges in a dynamic way the keys during the use of the system. This protocol, associated with the vector of initialization much larger than in the WEP, prevents some attacks on WEP now well-known.

Protocol TKIP in the final analysis proves possible to circumvent. That requires much time: a few minutes of capture of packages and about 30.000 days of calculation on Pentium IV. However it is possible to accelerate research by using the Calcul distributed, thanks to clusters or machines zombies. The protocol CCMP, used in WPA2 , is thus to prefer.

In addition to the identification and coding, WPA guarantees also an integrity definitely improved of the data. The Cyclic redundancy check (CRC) used for the WEP is, in an intrinsic way, not very sure: it is possible to deteriorate the data and to update the CRC of the message without knowing key WEP. An algorithm of identification of the messages ( Message authentication codes or English MAC, but called MIC for Message Integrity Code within the framework of the WPA) protected is used for the WPA: it is about a fore-mentioned algorithm “Michael”. The MIC used for the WPA include, moreover, one meter of screen which prevents the attacks by rejeu, another weakness of the WEP.

The WPA was conceived like an intermediate stage on the way towards a better safety of standard 802.11. This for two reasons. Firstly, work on the standard 802.11i lasted much longer than envisaged, being spread out over four years during which concern about the safety of the wireless networkings went growing. Secondly, it gathers, in a subset of the standard 802.11i, the elements which are compatible with the WEP of the very first adapters 802.11b. Updates WPA were provided for the very large majority of the already existing charts Wi-Fi. The access points sold before 2003 generally need to be replaced.

While increasing the size of the keys and the vectors of initialization, by reducing the number of packages sent with key (Re) dependant, and by adding a mechanism of identification of the messages, the WPA returns the penetration of a lan without wire much more difficult. The Michael algorithm is the most resistant algorithm that the originators of the WPA could include without giving up compatibility with the majority of the old charts networks. However, this algorithm is prone to an attack by counterfeit of packages. To limit this risk, networks WPA stop during 30 seconds as soon as an attempt at attack is detected.

WPA2

WPA2 is the version of the standard IEEE 802.11i certified by Wi-Fi Alliance. WPA2 includes all the obligatory elements of the standard 802.11i. In particular, WPA2 rather uses a coding based on AES than on RC4. The protocol based on AES, CCMP, is regarded as protected completion: in May 2004, the NIST (National Institute of Standards and Technology) approved it.

The official assumption of responsibility of WPA2 in Microsoft Windows XP was announced on May 1st, 2005. An update of the pilots for charts network can prove to be necessary. Apple, Inc. deals with the WPA2 on all the Macintoshs comprising a chart AirPort Extreme, on the AirPort Extreme Bases Station , and the AirPort Express . The updates of the firmware necessary are included in AirPort 4.2 , left on July 14th, 2005.

Safety in the mode pre-shared key

The mode pre-shared key (PSK, so known as Personal mode) was conceived for the individual networks or of SME which cannot allow the cost and the complexity of a solution using a waiter of identification 802.1X. Each user must seize a secret Phrase to reach the network. The secret sentence can contain from 8 to 63 characters ASCII or 64 hexadecimal symbols (256 bits). A key given in the form of characters ASCII is converted towards the key of 256 bits thanks to a cryptographic Fonction of chopping (the Pairwise Master Key , PMK). To use a random succession of hexadecimal natures remains surer (indeed, a passphrase remains, all things considered, prone to an attack by dictionary), but the key is then more difficult to write and retain. The majority of the operating systems make it possible the user to store the secret sentence on the computer in order not to have to again seize it but however in form PMK, i.e. already chopped. The secret sentence must remain stored in the Access point Wi-Fi.

Safety is reinforced by the use of a function PBKDF2 of generation of derived keys. However, the secret sentences that the users are accustomed to using make the system vulnerable to the attacks on the passwords. Programs carrying out this type of attack is available on Internet, it is the case of WPA Cracker. These attacks can be thwarted while using jointly with WPA and WPA2 a secrecy of at least 5 words generated by the method completely random Diceware or 14 characters. For a maximum safety, 8 words generated by the Diceware method or 22 randomness should be used. The secret sentences would owe, moreover, being changed as soon as a person having an access to the network is not authorized any more to use it or many only one equipment connected to the network is lost or compromised.

Certain manufacturers tried to avoid employment by the users of secret sentences weak by providing a procedure allowing to generate and distribute robust keys. This procedure is accessible by the means of a software or material interface using an external mechanism to add a Wi-Fi adapter to a network. These mechanisms include the pressure of a button (for Broadcom SecureEasySetup and Buffalo AirStation One-Touch Secure Setup) and the software seizure of a challenge (for Atheros JumpStart).

Various mechanisms EAP available for WPA-Enterprise and WPA2-Enterprise

Wi-Fi Alliance announced the inclusion of mechanisms EAP (Extensible Authentication Protocol) additional in its programme of certification for the modes WPA-Enterprise and WPA2-Enterprise . Thus, there is the certainty that the certified products WPA-Enterprise can interopérer between them. Previously, only mechanism EAP-TLS (Transport To bush-hammer Security) was certified by Wi-Fi Alliance.

Various mechanisms EAP included in the program of certification are:

• EAP-TLS (previously tested)
• EAP-TTLS/MSCHAPv2
• PEAPv0/EAP-MSCHAPv2
• PEAPv1/EAP-GTC
• EAP-SIM

Other mechanisms EAP can be supported by the customers and the waiters 802.1X. This certification is an attempt to make interopérer the most current mechanisms EAP. The failure of Wi-Fi Alliance to carry out this interworking is currently one of the main issues preventing the deployment of solutions 802.1X within heterogeneous networks.

See too

• Wpa supplicant : a implementation of WPA on Linux, Windows (and BSD)
• - discussed the standard Chinese national for the safety of the networks wireless telegraphy
• - a waiter light RADIUS conceived to be embarked in an access point wireless telegraphy

; References

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