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Chapter 7: Physical-layer Key Encoding for Wireless Physical-layer Secret-key
Generation (WPSG) with Unequal Security Protection (USP)
used to achieve perfect secrecy in Section 7.3.
However, perfect secrecy for the key encoding scheme may require key input that is
too long to be economical, especially if the number of vulnerable key bits is large. In the
case of scalable data, such as video data, perfect secrecy is not required for the whole
data. Even though low-priority parts in the data do not have perfect secrecy, the enemy
cryptanalyst will have no idea at all about the data if high-priority parts are properly
protected. From now on, we will call this concept “scalable security” or “unequal security
protection (USP).”
Previous research on scalable security is discussed in Section 7.4. After that, we propose
a new framework in Section 7.5 to provide scalable security services to the application
layer. This framework allows the application layer to specify some design parameters according
to its scalable security requirements, which, as shown in Sections 7.6 and 7.7,
can be realized in the contexts of secure network coding and physical-layer key encoding,
respectively. In the end, Section 7.8 concludes the chapter and suggests some future
research.
7.1 Introduction to Physical-layer Key Encoding for
a One-Time-Pad Encryptor
As demonstrated in Sections 6.2 and 6.5 of Chapter 6, vulnerable key symbols that can be
estimated by an eavesdropper exist in high proportion if there are too few scatterers in the
environment, the eavesdropper is located near either the transmitter or the receiver, or,
in the case of relay communication, the pilot transmission protocol is insecure. Moreover,
although the eavesdropper is nowhere near the transmitter or receiver during transmission,
he or she may have been there before and it is possible that channel coefficients (especially
the amplitudes) do not change much. Therefore, assuming that he or she can correctly
predict some key symbols, we should try to find some countermeasures. To do so, we
adopt a similar concept to Shamir’s secret sharing [9] and Cai and Yeung’s secure network