Wireless Network Security Wireless LAN Security Slide from 2 nd book 1
802.11 Wireless LAN Security Stations in LAN are connected physically while in WLAN any station in the radio range is connected, so in WLAN extra care should be considered because 1. Authentication in LAN is much robust since all sending stations are wired and already known. 2. Privacy problem in WLAN, since any station comes in the range of WLAN can send and receive messages. The original 802.11 specification included a set of security features for privacy and authentication that were quite weak. Wi-Fi Protected Access (WPA) as a Wi-Fi standard. WPA is a set of security mechanisms that eliminates most 802.11 security issues. The final form of the 802.11i standard is referred to as Robust Security Network (RSN).
802.11i RSN Services and Protocols The 802.11i RSN security specification defines the following services: Authentication: A protocol is used to define an exchange between a user and an AS that provides mutual authentication and generates temporary keys to be used between the client and the AP over the wireless link. Access control: This function enforces the use of the authentication function, routes the messages properly, and facilitates key exchange. It can work with a variety of authentication protocols. Privacy with message integrity: MAC-level data (e.g., an LLC PDU) are encrypted, along with a message integrity code that ensures that the data have not been altered. 3
802.11i Phases of Operation IEEE 802.11i security is concerned only with Station and Access Point. The five phase are: Discovery: 1. An AP uses messages called Beacons and Probe Responses to advertise its IEEE 802.11i security policy. 2. The STA uses these to identify an AP for a WLAN with which it wishes to communicate. 3. The STA associates with the AP, which it uses to select the cipher suite and authentication mechanism when the Beacons and Probe Responses present a choice.
802.11i Phases of Operation Authentication: the STA and AS (Authentication) prove their identities to each other. The AP blocks non-authentication traffic between the STA and AS until the authentication transaction is successful. The AP does not participate in the authentication transaction other than forwarding traffic between the STA and AS.
802.11i Phases of Operation Key generation and distribution: The AP and the STA perform several operations that cause cryptographic keys to be generated and placed on the AP and the STA. Frames are exchanged between the AP and STA only 6
802.11i Phases of Operation Protected data transfer: Frames are exchanged between the STA and the end station through the AP. As denoted by the shading and the encryption module icon, secure data transfer occurs between the STA and the AP only; security is not provided end-to-end. 7
802.11i Phases of Operation Connection termination: The AP and STA exchange frames. During this phase, the secure connection is torn down and the connection is restored to the original state.. 8
802.11i Discovery Phases The purpose of this phase is for an STA and an AP to 1. Recognize each other 2. Agree on a set of security capabilities Confidentiality MPDU integrity protocols Authentication method Cryptography key management approach 3. Establish an association for future communication using those security capabilities Discovery phase consists of three exchanges: 1. Network and security capability discovery. 2. Open system authentication. 3. Association. 9
802.11i Discovery Phases 1. Network and security capability discovery. AP priodicaly broadcast its security capabilities through Beacon frame. SATS discover the access point by either 1. Monitoring Beacon frame. 2. Sending Prob frame. 10
802.11i Discovery Phases 2. Open system authentication STA & AP exchange their IDs 3.Association To Agree on set of security suit to be used. 11
802.11i Authentication Phases The authentication phase enables mutual authentication between an STA and an authentication server (AS) located in the DS. Authentication is designed to 1. allow only authorized stations to use the network 2. and to provide the STA with assurance that it is communicating with a legitimate network Authentication phase consists of three exchanges: 1. Connect to AS. 2. EAP exchange. 3. Secure Key Delivery. 12
802.11i Authentication Phases 1. Connect to AS. STA sends To it AP a request for connection to the AS. AP acknowledge this request this request and forward it to AS. 2. EAP ( Extensible authentication protocol) exchange : This exchange authenticates STA and AS. 3. Secure Key Delivery: After authentication AS will generate Master key session (MSK) and send it to STA. All cryptographic keys used by STA will be derived from MSK. 13
During the key management phase, a variety of cryptographic keys are generated and distributed to STAs. Pairwise keys are used for communication between a pair of devices, typically between an STA and an AP. 802.11i Key Management Phases These keys form a hierarchy, beginning with a master key from which other keys are derived dynamically and used for a limited period of time. 1. A pre-shared key (PSK) is a secret key shared by the AP and a STA 2. The other alternative is the master session key (MSK), which is generated using the IEEE 802.1X protocol during the authentication phase, as described previously. 14
802.11i Key Management Phases The pairwise master key (PMK) is derived from the master key as follows: 1. If a PSK is used, then the PSK is used as the PMK; 2. if a MSK is used, then the PMK is derived from the MSK by truncation (if necessary). By the end of the authentication phase (on EAP Success message), both the AP and the STA have a copy of their shared PMK. The PMK is used to generate the pairwise transient key (PTK), to be used for communication between an STA and AP after they have mutually authenticated. PTK = HMAC( PMK the MAC addresses of the STA and AP nonces ). 15