الفهرس 
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Abstract
Identification Friend or Foe (IFF) is a radar transponder installed in a combat
aircraft which authentically responses to a coded message identifying the aircraft as
friend or foe. The thesis consists of three parts.
The first part proposes a new chaos Advanced Encryption Standard AES
algorithm for data security. The algorithm is based on substituting the Rijndael affine
transformation S-box by another one based on chaos theory. The new S-box has a low
correlation and exhibits a significant performance improvement with an acceptable
complexity addition. The algorithm is tested using the commonly used tests for
determining whether the binary sequence possesses some specific characteristics that
a truly random sequence would be likely to exhibit. These are frequency, runs, serial,
autocorrelation and poker tests, respectively. These statistical tests are performed with
random and uniform distribution plaintext data. TI1e results of the proposed chaos
AES were compared with a normal one and gave a significant improvement for the
accepted sequences probability over a wide range of chaos initial conditions. The
sensitivity of the initial condition gives the algorithm the ability to be used as another
key for more security and confidentiality.
The second part introduces a new technique for aircraft IFF. The technique is
based on using a proposed chaos AES with mode-S IFF. AES has a key size of 128
bits and a substitution-linear transformation network with 10 rounds. The sensitivity
of the chaos initial condition gives the algorithm the ability to use as a second key.
The first key was assigned using a soft look-up table used periodically. The second
key was assigned using the date of the current day by both interrogator and the
transponder. This technique gives the system more security and confidentiality which
is compatible with mode-S IFF interrogation and reply messages format. It requests a
new data on the reply signal. This data increase the radar performance for detection
and tracking the friend targets in active and passive jamming environments. TI1e
results obtained from this technique on the simulated interrogator and transponder
signals shows that this scheme can be easily implemented and provide the air defence
system a secured aircraft authentication