Method and system for converting input data block into output data block by encryption

Abstract

An input data block is cryptographically converted into an output data block; by performing a non-linear operation on the input data block using an S-box based on permutations. The S-box is associated with a set of at least two permutations. Each time before the S-box is used, one of the permutations is (pseudo-)randomly selected from the set of permutations and used for the conversion.

Description

technical field [0001] The present invention relates to methods and systems for encrypting an input data block into an output data block. Background technique [0002] The application of encryption in the field of copyright protection of digital audio and / or video becomes particularly important. These applications include content encryption / decryption and access management functions. For these applications the well known block cipher DES can be used. DES is a Feistel cipher with 16 cycles. In each cycle, the first 32 bits of the right half of the data are expanded to 48 bits. A 48 bit round key calculated from a 56 bit DES key using the scheduling algorithm is added bit by bit to the above 48 bit modulo 2. Then, the S-box layer performs a non-linear operation on the data. In DES, the S-box layer includes eight parallel 6 to 4-bit S-boxes, that is, each S-box uses its fixed mapping table to convert a 6-bit input block into a 4-bit output block. The output of the S-box l...

AI Technical Summary

Problems solved by technology

It has been shown that DES cannot be enhanced against these attacks by modifying the key length and / or key scheduling algorithm

However, changing the round function of the algorithm (e.g. in the S-box) can significantly affect its strength against these attacks

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