Prior to the introduction of IEEE 802.11i, the security scheme for IEEE 802.11 w
ID: 3650305 • Letter: P
Question
Prior to the introduction of IEEE 802.11i, the security scheme for IEEE802.11 was Wired Equivalent Privacy (WEP). WEP assumed all devices in
the network share a secret key.The purpose of the authentication scenario is
for the STA to prove that it possesses the secret key. Authentication proceeds
as shown in Figure 6.23.The STA sends a message to the AP requesting
authentication. The AP issues a challenge, which is a sequence of 128
random bytes sent as plaintext. The STA encrypts the challenge with the
shared key and returns it to the AP.The AP decrypts the incoming value and
compares it to the challenge that it sent. If there is a match, the AP confirms
that authentication has succeeded
a. What are the benefits of this authentication scheme?
Explanation / Answer
Wireless security is the prevention of unauthorized access or damage to computers using wireless networks. The most common types of wireless security are Wired Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA). WEP is one of the least secure forms of security. A network that is secured with WEP has been cracked in 3 minutes by the FBI.[1] WEP is an old IEEE 802.11 standard from 1999 which was outdated in 2003 by WPA or Wi-Fi Protected Access. WPA was a quick alternative to improve security over WEP. The current standard is WPA2; some hardware cannot support WPA2 without firmware upgrade or replacement. WPA2 uses an encryption device which encrypts the network with a 256 bit key; the longer key length improves security over WEP. Many laptop computers have wireless cards pre-installed. The ability to enter a network while mobile has great benefits. However, wireless networking is prone to some security issues.[2] Crackers have found wireless networks relatively easy to break into, and even use wireless technology to crack into wired networks.[3] As a result, it's very important that enterprises define effective wireless security policies that guard against unauthorized access to important resources.[4] Wireless Intrusion Prevention Systems (WIPS) or Wireless Intrusion Detection Systems (WIDS) are commonly used to enforce wireless security policies. The risks to users of wireless technology have increased as the service has become more popular. There were relatively few dangers when wireless technology was first introduced. Crackers had not yet had time to latch on to the new technology and wireless was not commonly found in the work place. However, there are a great number of security risks associated with the current wireless protocols and encryption methods, and in the carelessness and ignorance that exists at the user and corporate IT level.[5] Cracking methods have become much more sophisticated and innovative with wireless. Cracking has also become much easier and more accessible with easy-to-use Windows or Linux-based tools being made available on the web at no charge. Some organizations that have no wireless access points installed do not feel that they need to address wireless security concerns. In-Stat MDR and META Group have estimated that 95% of all corporate laptop computers that were planned to be purchased in 2005 were equipped with wireless. Issues can arise in a supposedly non-wireless organization when a wireless laptop is plugged into the corporate network. A cracker could sit out in the parking lot and gather info from it through laptops and/or other devices as handhelds, or even break in through this wireless card-equipped laptop and gain access to the wired network. In public-key cryptography, the Station-to-Station (STS) protocol is a cryptographic key agreement scheme based on classic Diffie-Hellman that provides mutual key and entity authentication. In addition to protecting the established key from an attacker, the STS protocol uses no timestamps and provides perfect forward secrecy. It also entails two-way explicit key confirmation, making it an authenticated key agreement with key confirmation (AKC) protocol. STS was originally presented in 1987 in the context of ISDN security (O'Higgins et al. 1987), finalized in 1989 and generally presented by Whitfield Diffie, Paul C. van Oorschot and Michael J. Wiener in 1992. The historical context for the protocol is also discussed in Diffie (1988). Supposing all setup data has been shared, the STS protocol proceeds as follows. If a step cannot be completed, the protocol immediately stops. All exponentials are in the group specified by p. Alice generates a random number x and computes and sends the exponential gx to Bob. Bob generates a random number y and computes the exponential gy. Bob computes the shared secret key K = (gx)y. Bob concatenates the exponentials (gy, gx) (order is important), signs them using his asymmetric key B, and then encrypts them with K. He sends the ciphertext along with his own exponential gy to Alice. Alice computes the shared secret key K = (gy)x. Alice decrypts and verifies Bob's signature. Alice concatenates the exponentials (gx, gy) (order is important), signs them using her asymmetric key A, and then encrypts them with K. She sends the ciphertext to Bob. Bob decrypts and verifies Alice's signature. Alice and Bob are now mutually authenticated and have a shared secret. This secret, K, can then be used to encrypt further communication. The basic form of the protocol is formalized in the following three steps: (1) Alice ? Bob : gx (2) Alice ? Bob : gy, EK(SB(gy, gx)) (3) Alice ? Bob : EK(SA(gx, gy)) [edit]Full STS Setup data can also be incorporated into the protocol itself. Public key certificates may be sent in steps 2 and 3 if the keys are not known in advance. (1) Alice ? Bob : gx (2) Alice ? Bob : gy, CertB, EK(SB(gy, gx)) (3) Alice ? Bob : CertA, EK(SA(gx, gy)) If system-wide key establishment parameters are not used, the initiator and responder may create and send their own parameters. In this case, parameters should be sent with the exponential. (1) Alice ? Bob : g, p, gx They must also be verified by Bob to prevent an active attacker from inserting weak parameters (and thus a weak key K). Diffie, van Oorschot & Wiener (1992) recommend against special checks to prevent this and instead suggest including the group parameters in Alice's certificate. [edit]Variations The variations mentioned here are from the original STS paper. See the following references for other, more significant variations. Bellare, M.; Canetti, R.; Krawczyk, H. (1998), "A modular approach to the design and analysis of authentication and key exchange protocols", Proceedings of the 30th Annual Symposium on the Theory of Computing RFC 2412, "The OAKLEY Key Determination Protocol". ISO/IEC 117703, "Mechanisms Using Asymmetric Techniques", (1999). [edit]Authentication-only STS A simplified form of STS is available that provides mutual authentication but does not produce a shared secret. It uses random number challenges instead of the above Diffie-Hellman technique. Alice generates a random number x sends it to Bob. Bob generates a random number y. Bob concatenates the random numbers (y, x) (order is important) and signs them using his asymmetric key B. He sends the signature along with his own random number to Alice. Alice verifies Bob's signature. Alice concatenates the random numbers (x, y) (order is important) and signs them using her asymmetric key A. She sends the signature to Bob. Bob verifies Alice's signature. Formally: (1) Alice ? Bob : x (2) Alice ? Bob : y, SB(y, x) (3) Alice ? Bob : SA(x, y) This protocol can be extended to include certificates as in Full STS. [edit]STS-MAC In cases where encryption is a not viable choice in session establishment, K can instead be used to create a MAC. (1) Alice ? Bob : gx (2) Alice ? Bob : gy, SB(gy, gx), MACK(SB(gy, gx)) (3) Alice ? Bob : SA(gx, gy), MACK(SA(gx, gy)) Blake-Wilson & Menezes (1999) note that this variation may be preferable to original STS ("STS-ENC") in any case because .. the use of encryption to provide key confirmation in STS-ENC is questionable — traditionally the sole goal of encryption is to provide confidentiality and if an encryption scheme is used to demonstrate possession of a key then it is shown by decryption, not by encryption. The paper goes on to counsel, however, that using K for both a MAC and as the session key violates the principle that keys should not be used for more than one purpose, and presents various workarounds.
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