Wireless Network Security WEP And Beyond Heidi Parsaye

Wireless Network Security: WEP And Beyond Heidi Parsaye Jason De. Vries Roxanne Ilse Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Outline • Wireless networking basics – Attempts at making wireless networking secure • Wired Equivalent Privacy – Why it’s no longer private – Brief overview of how to crack • Beyond WEP – Wi. Fi Protected Access (WPA) Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Wireless Broadband • How Does Wireless Broadband Work? • Benefits of Wireless Broadband • Disadvantage of Wireless Broadband Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Wireless Network Security • IEEE 802. 11 WI-FI • Wired Equivalent Privacy (WEP) • TKIP (Temporal Key Integrity Protocol) • MAC address filtering • Wi-Fi Protected Access (WPA and WPA 2) Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Encryption Of WEP Data Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Decryption Of WEP Data Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Important Details About WEP Frames Plaintext • BSSID • Initialization Vector • Destination Address Encrypted • LLC Header • SNAP Header • Data • 32 -bit CRC • All 802. 11 WEP frames contain a plaintext header followed by encrypted data. • The Initialization Vector is included in the plaintext. • There is no CRC on the plaintext header. We can easily spoof the BSSID to get around MAC address filtering. • No attempt is made to hide packet lengths. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Important Details About WEP Frames • The RC 4 Initialization Vector must be sent in plaintext. The recipient needs to be combine it with the secret key to re -create the state array used for decryption. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

The Problem With WEP • It’s actually a problem with RSA RC 4 which was designed in 1987 by Ron Rivest (the R in RSA). • In 2001, Scott Fluhrer, Itsik Mantin, and Adi Shamir (the S in RSA) discovered that the first few bytes of the RC 4 data are non-random and leak information about the key. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

The Problem With RC 4 • The “Secret Key” used by KSA is actually the Initialization Vector (3 bytes) plus the Secret Key (5 or 13 bytes). • Since we know the first three values, we know the output for the first three iterations of KSA. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

The Problem With RC 4 • If we can get the state array, we can now start plugging data into PRGA. More specifically, we can start running it in reverse to give us a hint about the secret key. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Another Weakness Plaintext • BSSID • Initialization Vector • Destination Address Encrypted • LLC Header • SNAP Header • Data • 32 -bit CRC • The 3 -byte LLC Header is always the same on every frame, starting with 0 x. AA, indicating that SNAP is next. • In fact, with a certain message we’ll cover later, we know the values for 16 of the encrypted bytes. • Knowing some of the encrypted plaintext makes the job even easier. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Getting The Secret Key • What we really need to see is the exact same plaintext message encrypted thousands of times using different Initialization Vectors. • If we get enough unique Initialization Vectors, we can crack the secret key. • But how do we get a WEP network to encrypt and transmit the exact same message thousands of times? – The answer: Ask the network the same question… get the same answer thousands of times! Heidi Parsaye - Jason De. Vries - Roxanne Ilse

We Have Ways Of Making You Talk • Ok, so what question can we ask the network thousands of times and get the same answer? – Hey network… what’s my IP address? This is known as an ARP request. • Since we don’t have the secret key, we can’t encrypt our own ARP request. • That means we need to steal a legitimate ARP request from the network. Once we get one, we’ll replay it thousands of times. We’ll force the network to talk to us as it replies to these requests… generating messages for us. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

ARP Requests • But if the data is encrypted, how could we find and read an ARP request? – The answer: We don’t need to read it or decrypt its content. We just need to recognize it as what we need. • Two facts about ARP requests help us: – They’re always the same fixed length. We can look for that. – It will be sent to a broadcast address. Remember, the destination MAC address is sent as plaintext in the 802. 11 header so we can read that part. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Retransmitting ARP Requests Plaintext • BSSID • Initialization Vector • Destination Address Encrypted • LLC Header • SNAP Header • Data • 32 -bit CRC • Look at the 802. 11 frame again. Once we steal a legitimate ARP request, there’s absolutely nothing to keep us from spoofing our BSSID and retransmitting the exact same request as many times as we want. • We don’t know the values of the encrypted bytes we’re transmitting, but that’s ok. We don’t care. • We also won’t be able to read the ARP reply sent by the network. We don’t care about the contents. The important part is that they are the same every time. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Recent Work • In 2005, Andreas Klein extended the 2001 work of Fluhrer, Mantin, and Shamir. He found additional correlations between the encrypted data and the secret key. However, his method still relied on educated guesses to compute all bytes of the secret key sequentially. – If while computing the 10 th byte it turns out you made an incorrect guess on the 4 th byte, you have to throw out all computations done from the 4 th byte onward and start again. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Recent Work • In 2007, Erik Tews, Ralf-Philipp Weinmann, and Andrei Pyshkin optimized Klein’s 2005 attack for usage against WEP. – Most notably, they modified the attack such that it is possible to compute the secret key bytes independently, instead of sequentially… much more efficient, less wasted computations. – Working at 802. 11 g data rates, they showed they could crack 128 -bit WEP with just 85, 000 packets, a success rate of 95%. . . in less than 60 seconds. Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Using Air. Crack Heidi Parsaye - Jason De. Vries - Roxanne Ilse

Beyond WEP – WPA 2 • Implements mandatory elements of 802. 11 i • Available in personal (SOHO) and enterprise mode • Uses AES (Advanced Encryption Standards) Heidi Parsaye - Jason De. Vries - Roxanne Ilse

WPA 2 Components • WPA 2 Wi-Fi certified client devices; may require software/hardware upgrades • Client supplicant, such as Microsoft or Funk Odyssey • EAP Authentication Types • WPA 2 -Enterprise Wi-Fi Certified APs; may require firmware or hardware upgrade • Authentication Server (RADIUS)/Database (SQL, LDAP or AD) Heidi Parsaye - Jason De. Vries - Roxanne Ilse

How WPA 2 Works • Initiated when user associates with an AP • User must authenticate first before AP will allow access to network • Authentication process enabled by IEEE 802. 1 X/EAP framework • Client & authentication server mutually authenticate with each other via the AP • Once authenticated, the authentication server & client simultaneously generate a “Pairwise Master Key” (PMK) • 4 -way handshake between client and AP to complete authentication and establish AES encryption keys to encrypt data exchanged between client and AP Heidi Parsaye - Jason De. Vries - Roxanne Ilse