Transcript Security in Wireless Networks

Security in Wireless Networks
IEEE 802.11i
Presented by Sean Goggin
March 1, 2005
Overview
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Inherent Problems in Wireless
Is WEP Really Equivalent?
Additional Solutions
802.11i – A New Solution
Conclusion
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Sean Goggin
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Inherent Problems in Wireless
• Modern Wired Network
– Multiple Nodes Interconnected with CAT-5, RG-58,
Fiber, and Etc.
– Typically Difficult to Intercept
Data
CAT 5e
Data
Computer A
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Computer B
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Inherent Problems in Wireless
• Modern Wireless Network
– Multiple Nodes Interconnected Over Radio Frequency
– Lacks Simplest Form of Physical Protection
Da t a
Da t a
Computer A
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Computer B
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Inherent Problems in Wireless
• Denial-of-Service Attack (DOS Attack)
– Media is Open to the Public
– Easily Disrupted, Compromises Availability
– Only Solution is to Locate and Disable
Computer A
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Intruder
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Computer B
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Inherent Problems in Wireless
• Man-in-the-Middle Attack (MITM Attack)
– Easily Intercepted
– Compromises Integrity and Confidentially
– Mitigate with use of Encryption
Da t a
Computer A
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Da t a
Intruder
Sean Goggin
Computer B
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Inherent Problems in Wireless
• Do to the Nature of Wired vs. Wireless,
Wired is More Secure
• Wireless Requires Protocol to Increase
Security
• IEEE & Wired Equivalent Privacy
– 40-bit (Exportable) and 104-bit Key
– RC4
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Is WEP Really Equivalent?
• IEEE Selects RC4 Cipher for WEP
• RC4 is a Stream Cipher System
– Utilizes a Shared Key and Pseudo Random Number Generator
(PRNG) to Create Keystream to XOR with Source’s Data, then
Sends Cipher Text
– Destination Utilizes the Shared Key and PRNG to Create
Keystream to XOR Cipher Text and Decrypt Source’s Data
Courtesy of 802.11 Wireless Networks: The Definitive Guide
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Is WEP Really Equivalent?
• WEP Process
– 40-bit Key + 24-bit Initialization Vector (IV) =
64-bit RC4 Key
– RC4 Key and PRNG Create Keystream Equal
in Length to Plain Text + CRC
– Keystream XORed with Plain Text and CRC
Value
– Transmit IV + Cipher Text
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Is WEP Really Equivalent?
• Key Management Issue
– Up to 4 WEP Keys Can Be Used
– Scalability vs. Security
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Manually Configure 1-4 Keys in an Enterprise
Manually Distribute 1-4 Keys to an Enterprise
Terminated Employees
Public Keys & Monitoring Station
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Is WEP Really Equivalent?
• Encryption Issue
– “Weaknesses in the Key Scheduling Algorithm
of RC4 “ by Fluhrer, Mantin, and Shamir
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Addressed Poor Implementation of RC4 in WEP
Weak IVs are Poorly Chosen and Repeated
Reused Keys Make Crypt Analysis Possible
Function is Linear, not Exponential
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Is WEP Really Equivalent?
• Attacking WEP
– The Key is Comprised of 5 Bytes or 13 Bytes
– The First Byte
• LLC Encapsulation & SNAP Header (00xA)
• (00xA) XOR First Byte of Cipher Text = First Byte
of Keystream
– The Remaining Bytes
• Weak IVs in form of B+3:FF:N
– B Refers to the Byte of the Key
– FF is Weak Middle Byte of all 1s
– N is any value from 0 to 255
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Is WEP Really Equivalent?
• Attacking WEP, Continued
– The Remaining Bytes, Continued
• Gather Weak IVs into Groups of B
– 5 Groups for 40-bit, 13 Groups for 104-bit
– Takes Approximately 115 Samples Per Group to Crack a Byte
of the Key
• Even Though More Weak IVs are Needed for 104-bit Key, it
Provides More Weak IVs by Nature
• Cracking 104-bit vs. 40-bit Takes More Time, But Insignificant
Amount
• More Wireless Network Traffic, Faster Weak IVs Appear
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Is WEP Really Equivalent?
• Tools to Crack WEP
– AirSnort
• Developed by Bruestle & Hegerle to Demonstrate
Work Done by Fluhrer, Mantin, and Shamir
• Capture Component
– Captures Raw Packets using Wireless Interface
• Crack Component
– Performs Analysis and Cracks Bytes of Key
– WEPCrack & dweputils
• Similar Functions as AirSnort
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Is WEP Really Equivalent?
• Other Attacks
– Simple XOR Attack
• Cipher Text is Plain Text XOR Keystream
• If a Known Plain Text is then XOR with Cipher Text
the KeyStream will be Exposed
– Use SPAM, Heavy Virus Network Traffic (ie: Sasser), or
Other Well-Known Network Traffic
• Used for Message Injection & Authentication
Spoofing
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Is WEP Really Equivalent?
• Other Attacks, Continued
– Brute-Force Attack
• Phrase Key Generators Often Flawed
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Uses ASCII Values to Seed the PRNG
ASCII Always Start with 0 and Range from 0 to 7F
7F vs FF… 21-bit vs. 32-bit Seed
Newsham Attacked 40-bit Key using P3/500, 35 Seconds
to Key
– Sometimes Applies to 104-bit Key Generator (MD5
Hash)
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Additional Solutions
• Best Practices
– Disabling SSID Beaconing
• SSID Beaconing Identifies AP to Wireless
Interfaces
• Easier for Legitimate Users and
Intruders/Attackers to Find AP
• Disabling SSID May Requires Additional
Configuration of User’s Interface
• Attacker can Detect Presence of AP, but without
SSID cannot Associate with AP
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Additional Solutions
• Best Practices, Continued
– MAC Authentication (CSUN)
• Legitimate Users Register MAC Address
• AP Disregard Packets from Non-Registered MAC
– Problems
• Both SSID and Legitimate MAC can be Gathered
with Network Sniffer and Wireless Card if Weak or
No Encryption Used
• WEP is Weak, So What is Left?
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Additional Solutions
• Virtual Private Network (VPN)
– Secure Data Above the Link-Layer
– May Require More Bandwidth
– Variety of Protocols
• IPsec (CSUN), SSL, & PPTP
• Wi-Fi Protected Access (WPA)
– After WEP was Exposed a Temporary
Solution was Needed
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Additional Solutions
• Wi-Fi Protected Access (WPA), Continued
– Wi-Fi Alliance Took Components of 802.11i
Draft
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Temporal Key Integrity Protocol
Larger IV (48-bit vs. 24-bit)
Message Integrity Check (MIC) Replaced CRC
802.1x or Pre-Shared Key (PSK)
RC4
– Could be Implemented on Existing Hardware
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802.11i – A New Solution
• Originally Meant to Address Security and
Quality of Service (QoS)
• Apparent Need for Additional Security
Created 802.11e QoS & 802.11i Security
• WPA is Released in April 2003 as
Temporary Solution Until 802.11i
Ratification
• 802.11i Ratified on June 24th, 2004
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802.11i – A New Solution
• Components of 802.11i
– 802.1x
– Advanced Encryption Standard in CounterMode/Cipher Block Chaining Message
Authentication Code Protocol (AES-CCMP)
– Temporal Key Integrity Protocol (TKIP)
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802.11i – A New Solution
• 802.1x
– Based on IETF Extensible Authentication
Protocol (EAP)
• Future Proof Open Standard
• Allows for Any Authentication Standard to be Used
• Designed to Regulate at Physical Port
– Point of Authenticating User & Network
– Typically Uses RADIUS
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802.11i – A New Solution
• 802.1x, Step 1
– Supplicant Request Association with Authenticator
– Authenticator Associates with Supplicant
– Authenticator Requests Identity from Supplicant via
EAP
EAP
Wireless
User
(Supplicant)
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AP
(Authenticator)
Authentication
Server
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802.11i – A New Solution
• 802.1x, Step 2
– Supplicant Responds with Identity to Authenticator via
EAP
– Authenticator Sends Access Request for Supplicant’s
Identity to Authentication Server via RADIUS
EAP
Wireless
User
(Supplicant)
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RADIUS
AP
(Authenticator)
Authentication
Server
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802.11i – A New Solution
• 802.1x, Step 3
– Authentication Server Validates Supplicant’s Identity
– Authentication Server Notifies Authenticator the Supplicant is
Valid and Issues Keying Material via RADIUS
– If Supplicant Fails to be Validated, Authentication Server Submits
Identity Request instead
RADIUS
Wireless
User
(Supplicant)
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AP
(Authenticator)
Authentication
Server
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802.11i – A New Solution
• 802.1x, Step 4
– The Authenticator Initiates a 4-Way Handshake with
Supplicant to Establish Keys
– Once Keys are Established the Supplicant is
Permitted to Access the Network
EAP
Wireless
User
(Supplicant)
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AP
(Authenticator)
Authentication
Server
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802.11i – A New Solution
• The 4-Way Handshake in 802.1x
– Terminology
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Master Key (MK)
Pairwise Master Key (PMK)
Authenticator Nonce (Anonce)
Supplicant Nonce (Snonce)
Pairwise Transient Key (PTK)
Group Temporal Key (GTK)
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802.11i – A New Solution
• The 4-Way Handshake in 802.1x
– Both the Supplicant and Authenticator have PMK Derived from
MK issued by the Authentication Server
– Step 1
• Authenticator Generates Anonce and Sends it to the Supplicant
PMK
Anonce
PMK
Anonce
AP
(Authenticator)
Wireless
User
(Supplicant)
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802.11i – A New Solution
• The 4-Way Handshake in 802.1x
– Step 2
• Supplicant Generates Snonce
• Supplicant Constructs PTK from Anonce, Snonce,
Authenticator MAC, Supplicant MAC, and PMK
• Supplicant Sends Snonce and MIC to Authenticator
PMK
Snonce + MIC
Anonce
PMK
Anonce
Snonce
PTK
AP
(Authenticator)
Wireless
User
(Supplicant)
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802.11i – A New Solution
• The 4-Way Handshake in 802.1x
– Step 3
• Authenticator Derives PTK from Anonce, Snonce,
Authenticator MAC, Supplicant MAC, and PMK
• Authenticator Constructs GTK from Above Data and Sends
GTK and MIC to Supplicant
PMK
GTK + MIC
Anonce
Anonce
Snonce
Snonce
PTK
PTK
GTK
AP
(Authenticator)
Wireless
User
(Supplicant)
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PMK
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802.11i – A New Solution
• The 4-Way Handshake in 802.1x
– Step 4
• Supplicant Sends ACK to Authenticator Concluding
Handshake Process
• Supplicant & Authenticator Have Established All Necessary
Keys
PMK
ACK
Anonce
Anonce
Snonce
Snonce
PTK
GTK
PTK
GTK
AP
(Authenticator)
Wireless
User
(Supplicant)
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PMK
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802.11i – A New Solution
• Pairwise Transient Key (PTK)
– Broken into 3 Keys
• Key Confirmation Key (KCK)
– Used to Compute and Confirm EAP MICs
• Key Encryption Key (KEK)
– Used for Encryption of EAP Data
• Temporal Key (TK)
– Used for Encryption of Supplicant-Authenticator Traffic
• Group Temporal Key (GTK)
– Used for Broadcast and Multicast Encryption
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802.11i – A New Solution
• Additional Features of 802.1x
– Key Caching
• Authenticator & Supplicant Cache Keys While
Roaming
• Prevents Excessive Load on Authentication Server
– Pre-Authentication
• If the Supplicant Sense the Next AP while
Roaming it can Begin Authentication via Network
to Next AP
• Reduces Association Time to Next AP
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802.11i – A New Solution
• AES-CM/CBC-MAC Protocol (AESCCMP)
– Features
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128-bit Advanced Encryption Standard
Counter-Mode
Cipher Block Chaining
48-bit Initialization Vectors
802.1x Key Assignment (TK from PTK)
Message Integrity Check
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802.11i – A New Solution
• Counter-Mode
– Turns a Block Cipher into a Stream Cipher
– Generates the Next Keystream Block by
Encrypting Successive Values of a Counter
– Counter is any Simple Function which
Produces Sequence which is Guaranteed not
to Repeat for a Long Time
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802.11i – A New Solution
Courtesy of: WikiPedia - Block cipher modes of operation
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802.11i – A New Solution
• Cipher Block Chaining
– Each Block of Plain Text is XORed with
Previous Block of Cipher Text Before Being
Encrypted
– Each Cipher Text Block is then Dependent on
the Blocks that Preceded
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802.11i – A New Solution
Courtesy of: WikiPedia - Block cipher modes of operation
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802.11i – A New Solution
• AES-CCMP, Continued
– AES-CM Provides Confidentiality
– CBC-MAC Provides Authentication & Integrity
– CCMP Protects Non-Encrypted Fields
• Such as Source & Destination Data
• Protects Against Replay Attack
– 16 Octets Larger then Non-Encrypted Data
• Slight Speed Decrease, Large Security Increase
– More Enterprise then Home Consumer
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802.11i – A New Solution
• AES-CCMP vs. WEP
– AES vs. RC4
– 128-bit vs. 104-bit Key
– Block Cipher vs. Stream Cipher
– 48-bit vs. 24-bit Initialization Vector
– CBC-MAC vs. RC4
– New vs. Established
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802.11i – A New Solution
• Temporal Key Integrity Protocol (TKIP)
– Features
• 128-bit RC4
• Per-Packet Key Mixing
• Enhanced Initialization Vectors including
Sequencing Rules
• 802.1x Key Assignment (TK from PTK)
• Michael MIC
• Runs on Legacy Hardware
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802.11i – A New Solution
Courtesy of: How Secure Is Your Wireless Network? Safeguarding Your Wi-Fi LAN
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802.11i – A New Solution
• TKIP – Phase 1
– Source MAC XORed with TK = Mixed Key
• TKIP – Phase 2
– Mixed Key XORed with Trip Sequence
Counter = Per-Packet Mixed Key
– Feed to WEP Engine as 128-bit Key
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802.11i – A New Solution
• Michael MIC
– 64-bit MIC Key, Source Address, Destination
Address, and Plain Text used to Generate 8
Byte MIC Hash
– MIC replaces CRC
– Plain Text+ MIC are Fed to WEP Engine as
Plain Text
• WEP Now Performs RC4 Operations
Using 128-bit Key and Plain Text + MIC
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802.11i – A New Solution
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802.11i – A New Solution
• Michael’s Countermeasure
– If CRC, Integrity Check Value, and IV Fail
Verification, Only then Check MIC
• Avoids False Positive
– If All Fail, Attack Underway
• Stop Using Current Keys & Re-Key
• Rate Limit Re-Keying to Once Per Minute
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802.11i – A New Solution
• AES-CCMP vs. TKIP
– AES vs. RC4
– Block vs. Stream Cipher
– CBC-MAC vs. RC4
– New Hardware vs. Existing Hardware
– New vs. Relatively New
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802.11i – A New Solution
• Additional Features of 802.11i
– Pre-Shared Key (PSK)
• Utilized instead of PMK, Less Secure?
• Home or Ad Hoc Network
– Password-to-Key Mapping
• Generates 256-bit PSK from ASCII
– Random Number Generation
• Established Minimum Guide Line
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802.11i – A New Solution
• 802.11i & WPA 2
– Wi-Fi Alliance Certification Program for
802.11i Compliance
– Possibly Misleading, WPA Hardware May Not
Be Compatible
• TKIP is in WPA & WPA 2
• Most WPA Hardware Not Capable of AES-CCMP
– User-Friendly Name for 802.11i
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Conclusion
• 802.11i Shows Promise, Only Proven with
Test of Time
• Performance/Security Trade-off Worth it?
• May Not Be as Important to Home Users
as it is for Enterprises
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Conclusion
• With Major Investment in Last 5 Years in
802.11b, New Hardware May Not Be
Adopted Promptly
• Why Buy 802.11i Instead of 802.16 or
802.20?
• Where is the Hardware?
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Questions & Answers
Security in Wireless Networks
802.11i
Next Time…
Advances in Optical Networks
SONET
April 19, 2005
References
• Wireless Security’s Future (PDF)
• Intercepting Mobile Communications: The
Insecurity of 802.11(PDF)
• IEEE 802.11i Overview (PDF)
• 802.11i and Wireless Security
• 802.11 Security
• Wikipedia – Block Cipher Modes of Operation
• Wikipedia – Advanced Encryption Standard
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