A secure key dependent dynamic substitution method for symmetric cryptosystems.

Area of Science:

• Cryptography
• Information Security
• Computer Science

Background:

• Static substitution S-boxes in symmetric cryptosystems present vulnerabilities to attacks.
• Existing dynamic key-dependent S-boxes often lack sufficient dynamicity and optimal security.

Purpose of the Study:

• To propose an effective and secure method for designing key-dependent dynamic S-boxes with dynamic permutations.
• To enhance the security of symmetric block ciphers against cryptanalytic attacks.

Main Methods:

• Developed a novel key-dependent dynamic S-box design incorporating dynamic permutations.
• Evaluated the S-box through criteria like bit independence, non-linearity, Hamming distance, and balanced output.
• Assessed randomness using National Institute of Standards and Technology (NIST) statistical tests and analyzed differential and linear approximation probabilities.

Main Results:

• The proposed S-box exhibits effective randomness properties and a significant avalanche effect (up to 62.32%).
• Demonstrated high sensitivity to the secret key, with a single bit change generating a completely new S-box.
• Experimental evaluations confirmed superior performance compared to existing S-box techniques.

Conclusions:

• The proposed dynamic S-box design offers optimal security for symmetric block ciphers.
• The method provides enhanced resistance to attacks due to its key-dependent nature and improved cryptographic properties.
• Future work can extend the method for larger key sizes (192-256 bits).