Wireless Vulnerabilities & Exploits
Wireless Vulnerabilities & Exploits
WVE ID: WVE-2005-0021
Type: Vulnerability
Status: Candidate
Classification:
Cryptographic
Design Flaw
Description:
The WEP encryption system used by 802.11 networks utilizes RC4 in a flawed manner which can lead to a WEP key becoming compromised.
Discussion:
The WEP encryption algorithm utilizes the RC4 cipher to ensure confidentiality of transmitted data. WEP encrypted data frames are constructed by concatenating a 24 bit initialization vector (IV) with a shared secret known only to those participating in the network. This shared key can be either 40 or 104 bits giving a total of either 64 or 128 bits of input data into the RC4 algorithm respectively. The reason for using an IV is to prevent the same key from encrypting the same data more than once, which if observed could lead to a compromise of the key.
The output of the RC4 algorithm, called the keystream, is then bitwise XOR-ed with the plaintext payload. However in order for the reciever to decrypt the ciphertext successfully it needs to know the IV that was used in the encryption process. Thus the IV is sent in an unencrypted form to the receiver.
The problem with this arises from an observations made in Fluhrer, Mantin, and Shamir's (FMS's) paper titled "Weaknesses in the Key Scheduling Algorithm of RC4." This paper showed that the first byte of a subset of IVs (deemed "weak") could be correlated with individual bytes of the secret key at a probability of 5%. Thus if enough frames containing these IVs are gathered, they can then be statistically analyzed to derive the secret key used for encryption.
Credits
Author:
Scott
Fluhrer
(sfluhrer@cisco.com)
: Cisco Systems
Author:
Itsik
Mantin
(itsik@wisdmon.weizmann.ac.il)
: The Weizmann Institute
Author:
Adi
Shamir
(shamir@wisdom.weizmann.ac.il)
: The Weizmann Institute
References
URL:
http://www.drizzle.com/~aboba/IEEE/rc4_ksaproc.pdf
Released: 2001-08-16
Submitter
Andrew
Lockhart
(alockhart@networkchemistry.com)
: Network Chemistry
Submitted: Mon Oct 31 12:38:50 -0800 2005
Candidate Date: Mon Oct 31 12:39:27 -0800 2005
