wireless and email security csci 5857: encoding and encryption
TRANSCRIPT
Outline
• Wireless network security– Wireless LAN structures– Authentication – Key management
• DKIM email security– Authentication between ISPs
Wireless LAN Terminology
• Station: Device capable of IEEE 802.11 wireless connectivity (wireless laptop, etc.)
• Distribution System: Backbone system for long-distance communication (lines/satellite/etc.)
• Access point: Bridge between station and distribution system (or between stations in same BSS)
• Basic Service Set (BSS): Set of stations in range of access point
Wireless LAN Structure
• Differences from LAN security:
• Any transmission may be listened to by any device in range of access point
All transmissions must be secured
• Other wireless devices in range of AP can attempt to connect to it
Any device wishing to communicate through access point must be authenticated
802.11i RSN Services
• Access control:– Preventing access to
access point until authentication
• Authentication:– Mutual authentication between stations and access points,
and key generation• Privacy:
– Encrypting/hashing/etc. of messages to insure confidentiality/information integrity/etc.
Authentication Server
• Authentication server– Contacted by AP when station requests access– Uses authentication protocol to establish station identity– AP blocks communication with rest of network until
authentication complete
Discovery Phase
• Station contacts AP• Station passes security suite to AP (like SSL)• AP responds
with chosen algorithms
Authentication Phase
• Station sends request to AP for connection to authentication server
• Extensible authentication protocol (EAP) used for mutual authentication
Authentication Phase
• Extensible Authentication Protocol:– Based on challenge-response– Station and AS share secret information (such as
symmetric key)– AS sends challenge to station (via AP)– Station sends response– May repeat with multiple challenges (10 – 20) for
added protection against replay attacks
Key Management Phase
• Possible methods:– Station and AP already share pre-shared key (PSK)
previously installed on station– AS generates and sends master session key (MSK) to
station as part of EAP challenge response• Used to generate pairwise master key
Key Management Phase• HMAC-SHA1 used to generate Pairwise transient key from
– Pairwise master key– MAC address of station and AP (prevents replay attacks)
• PTK consists of– Key used for confirmation of other keys– Key used to encrypt other keys– Actual temporal key used to
securely transmit data
Key Management Phase
• Handshake between station and AP used to establish and confirm keys used for secure transmission
Domain Keys Identified Mail
• Proposed Internet Standard RFC 4871, has been widely adopted
• Goal: Minimize fake email sent– Email purportedly from another user trusted by recipient– Spam, fraud, viruses, etc.
• Signing/validation done at provider level– Individual users do not need to be involved in process
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Internet Mail Architecture
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Sender composes mail in mail client software
Mail client software sends email contents to sender’s ISP
Email sent to mail server of recipient’s ISP
Recipient retrieves email from their ISP’s server
DKIM Authentication
• Sender submits email to their ISP’s server
• Email signed by sending server using their public key
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