Network Coding and Wireless Physical-layer ... - Jacobs University

Chapter 7: Physical-layer Key Encoding for Wireless Physical-layer Secret-key
Generation (WPSG) with Unequal Security Protection (USP) 103
In [22, 32], a selective encryption scheme is used such that only the I-frames are encrypted.
However, empirical evidence in [27, 72] shows that the scheme is insecure. The
authors of [27] suggest that improvements can be made if some more parts in the data
are encrypted. Although this is a good compromise, the basic idea is the same.
It is important to note that the encryption scheme used in these works, such as Data
Encryption Standard (DES) and Rivest, Shamir, and Adleman (RSA) algorithm, only
provides practical, but not theoretical security. Any cryptanalyst who posseses an incredibly
large computing power can decrypt the secret data. Since we are interested in
theoretical security, our method used to achieve scalable security is different. The next
section provides the framework to our approach.
7.5 Scalability Framework in Theoretical Security
One normally thinks of a security concept as a dichotomy of being secure or insecure,
with nothing in between. In order to understand our framework, it is most important
to understand that absolute security and absolute insecurity are the two extremes of a
continuum of the guessing success probability.
Consider a piece of two-bit data, when we say that the data is absolutely secure, we
mean that the probability that the enemy can correctly guess the encrypted data is 0.25.
In contrast, it is absolutely insecure if such a probability, which will be called the guessing
success probability from now on, is 1.
Earlier frameworks based on selective encryption have only concepts of (practically)
absolute security and absolute insecurity.
According to our example, any encryption
scheme providing the guessing success probability p g such that 0.25 < p g < 1 cannot be
incorporated into those frameworks.
When the concept of guessing is included in the scalable security framework, the
guessing success probability p g becomes one security benchmark so that the security levels
of encryption schemes can be measured and compared. n-symbol data is absolutely secure
if p g = ( 1
|F| )n , where |F| is the field size of each symbol. It is absolutely insecure if p g = 1.