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초기화 벡터IV 충돌 |
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A major concern is the way that wired equivalent privacy WEP allocates the RC4 initialization vectors IVs used to create the keys that are used to drive a pseudo random number generator that is eventually used for encryption of the wireless data traffic. The IV in WEP is a 24-bit field - a small space that practically guarantees reuse, resulting in key reuse. The WEP standard also fails to specify how these IVs are assigned. Many wireless network cards reset these IVs to zero and then increment them by one for every use. If an attacker can capture two packets using the same IV the same key if the key has not been changed, mechanisms can be used to determine portions of the original packets. This and other weaknesses result in key reuse, resulting in susceptibility to attacks to determine the keys used. These attacks require a large number of packets 5-6 million to actually fully derive the WEP key, but on a large, busy network this can occur in a short time, perhaps in as quickly as 10 minutes although, even some of the largest corporate networks will likely require much more time than this to gather enough packets. In WEP-protected wireless networks, many times multiple, or all, stations use the same shared key. This increases the chances of IV collisions greatly. The result of this is that the network becomes insecure if the WEP keys are not changed often. This furthers the need for a WEP key management protocol. |