Oliynykov R. Methods for аnalysis and synthesis of perspective symmetric cryptographic transformations

The thesis is dedicated to solving of the important scientific problem of symmetric cryptographic transformations synthesis providing high level strength and performance. For main types of cryptanalytic attacks based on precomputed tables methods of table computation stage complexity estimation in conditions where the set cardinality of accounted unique elements is near to unknown state values set cardinality of cryptographic transformation are proposed for the first time. Comparison method of block cipher high level constructions allows selection of the best construction based on strength to number of encryption rounds ratio is proposed for the first time. Method of block ciphers synthesis based on secret non-surjective S-boxes allows keyless decryption for authorized party and provides security to encrypted message compromising to any other unauthorized party is proposed for the first time. Proposed synthesis method of block cipher key schedule provides non-bijective correspondence of round key and encryption key sets, protection from related keys attacks and improving strength to side-channel attacks, keeping security against brute force attacks. Proposed methods allow development of block cipher "Kalyna" and hash function "Kupyna" providing high level of cryptographic strength and performance exceeding international standards on 64-bit software implementations. These cryptographic transformations were used during Ukrainian national cryptographic standards project development.