Improved security of Rijndael key expansion function
Symmetric block ciphers are the most widely utilized cryptographic primitives. In most block ciphers, a master key of special length is manipulated to create round subkeys. This manipulation is known as the key schedule. A strong key schedule means that a cipher will be more resistant to various...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/69081/1/FSKTM%202018%2062%20IR.pdf |
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| Summary: | Symmetric block ciphers are the most widely utilized cryptographic primitives. In
most block ciphers, a master key of special length is manipulated to create round subkeys.
This manipulation is known as the key schedule. A strong key schedule means
that a cipher will be more resistant to various forms of attacks especially in relatedkey
model attacks. These days, the most common block cipher is Rijndael which
adopted by the National Institute of Standards and Technology (NIST), USA in 2001
as an Advance Encryption Standard (AES). Some cryptanalysis studies have also
revealed a security weakness of Rijndael such as its vulnerability to related-key
differential attacks and the related-key boomerang attack. This is mainly due to the
lack of nonlinearity in the key schedule of Rijndael. Constructing a key schedule that
is both efficient and provably secure has been an open problem for a long time. This
research presents a method to improve the key schedule of Rijndael cipher in order to
make the cipher resist to related-key scenario attack in form of differential
cryptanalysis attacks and boomerang attack. Two statistical tests are used: the first is
a Frequency test that evaluates the bit confusion property and the second is the Strict
Avalanche Criterion (SAC) test that evaluates the bit diffusion property. To evaluate
the resistance of the proposed approach to the related-key differential attack and the
related-key boomerang attacks, the MILP-based approach is developed. This method
counts the minimum number of active S-boxes (finds the related-key differential
characteristic) in a given number of rounds for byte-oriented block cipher in the
related-key model. The results show that the proposed key expansion function of has
excellent statistical properties and agrees with the concept of Shannon's diffusion and
confusion bits. The proposed approach is also resistant against the latest related-key
differential attacks and related-key boomerang attack found in the original Rijndael.
Furthermore, the proposed approach has a software implementation speed
approximate to the original Rijndael even in some applications where the key master
frequently changes for each processed data block. These results prove that proposed approach performs better than the original Rijndael 128-bit key expansion function
and that of previous research. |
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