wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

Industrial Wireless Communications Security (IWCS)/C42 28-3
Encryption transforms data from a readable form to a nonreadable form for humans. The key
length is an indicator for the strength of the encryption algorithm. Examples of encryption algorithms
include RC4 (Rivest Cypher 4), Data Encryption Standard (DES), Triple-DES, Blowfish, International
Data Encryption Algorithm (IDEA), Software-Optimized Encryption Algorithm (SEAL), RSA (Rivest
Shamir Adelman), and RC4. Encryption prevents eavesdropping of wirelessly transmitted data.
Radio communications are subject to jamming regardless of the form of wireless signal. APs monitor
channel quality and bit rate for other stations, which enables the detection of jamming. However, unless
APs have collaborative software for sharing and analyzing this information, the location of the attacker
cannot be identified.
Wireless signals radiate in free space and are subject to interception. Wireless laptop computers placed
near industrial enterprises can intercept WLAN signals, collect sensitive information, and potentially
disrupt the network.
Hijacking a wireless channel is a difficult task because the attacker must ensure that the two parties
cannot communicate with one another [7]. The two users must be out of wireless range or be
Âdesynchronized to set up a man in the middle (MITM) attack. In an MITM attack, the attacker must
eavesdrop on both users and impersonate each user to the other. One MITM attack approach would be
to jam the receiver of one user using a directional antenna while receiving the transmitted traffic from
another user.
28.2.2 Security Mechanisms
Security mechanisms and protocols are necessary to maintain the secrecy of data transmitted through
the air and to ensure that the data is not tampered with. Since the introduction of 802.11 WLAN, new
protocols have been developed as insecurities were found in existing deployed protocols (WEP, WPA,
WPA2, TKIP, CCMP, and WAPI). A survey of these protocols follows.
28.2.2.1 Wireless Encryption Protocol
The first security mechanism for WiFi is the wireless encryption protocol (WEP), which requires little
computational power. WEP is based on the RC4 encryption algorithm and is not as sophisticated as the
cryptographic protocols that follow. Researchers demonstrated the insecurity of WEP within the first
few years of its deployment [8].
WEP uses a symmetric secret key cipher, k, and an initialization vector, IV, to generate a keystream
(a pseudorandom sequence of bits) as shown in Figure 28.2.
The decryption key is identical to the encryption key in symmetric key algorithms. WEP is not scalable
due to a lack of automatic key management. The key is either 64 or 128 bits. An integrity checksum
is computed on the message/data and then the two are concatenated to create a plaintext. The keystream
is mathematically combined (Exclusive OR) with the plaintext to create a ciphertext. The ciphertext and
IV are transmitted between a sender and receiver. The receiver uses the identical secret key to recover
the message from the ciphertext. RC4 was developed in 1987 by Ron Rivest of RSA Security. The process
for the RC4 encryption and decryption is shown in Figure 28.3.
Plaintext
Message
|
CRC
Keystream
RC4 (IV, k)
Plaintext XOR keystream
IV
Ciphertext
FIGURE 28.2
Encrypted WEP frame.
© 2011 by Taylor and Francis Group, LLC