What is the key size for RC4 when it is utilized with WEP?

The key size for RC4 when utilized with WEP (Wired Equivalent Privacy) is primarily 40 bits. This choice is rooted in the historical context of the development of WEP, which was aimed at providing a level of security for wireless networks comparable to what was available for wired networks.

WEP implemented effective encryption through RC4, but due to regulatory constraints and the desire for broader adoption at the time, the initial key size was set at 40 bits. This smaller key size contributed to vulnerabilities, as it made the encryption easier to crack compared to larger key sizes.

Later implementations and updates to the WEP protocol allowed for up to 104 bits of key length, but the standard and its initial usage widely considered a 40-bit key size. Thus, the correct identification of 40 bits as the key size reflects the historical and functional aspects of how RC4 was originally integrated within WEP for wireless security.