Wireless Security.pdf - PDF Archive

466 Chapter 19
Initialize
key stream
generator
Initialize
Initialize
Run stream cipher key stream Run stream cipher key stream Run stream cipher
generator
generator
Figure 19.11: Bluetooth stream cipher periodicity
Initialize
key stream
generator
enough time for the key stream generator to be initialized. The overall timing sequence is
as shown in Figure 19.11 where “ running the stream cipher ” and “ initializing key stream
generator ” slots alternate.
19.2.6 Integrity Protection
The Bluetooth standard relies on a cyclic redundancy check (CRC) to provide message
integrity. Recall from Section 18.6 that WEP also used CRC for providing message
integrity. We discussed the loopholes of this approach in Section 18.7 and concluded that
using a linear noncryptographic integrity check mechanism like CRC leaves a lot to be
desired as far as integrity protection is concerned. We also saw that just encryption does
not automatically provide integrity. In other words, just because a message is encrypted
does not mean that it can’t be modified in-transit without the receiver’s knowledge.
The bottom line is that by choosing CRC, Bluetooth fails to provide any real 12 integrity
protection.
19.2.7 Enhancements
As we said at the beginning of this chapter, ad hoc networking technology is still in its
nascent stage. There are many issues to be resolved and security is such an issue. The
Bluetooth standard is also expected to evolve as ad hoc networking technology evolves.
12
That is, any strong enough.
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