Symmetric cryptographic system for data encryption
AssigneeNorthern Telecom Limited
InventorCarlisle M. Adams
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Abstract
A novel symmetric cryptographic system for data encryption using novel partially bent-function-based (m.times.n) substitution boxes (s-boxes), where m and n are positive even numbers, m<<n and m<log ##EQU1## is disclosed. A novel key schedule is used for selecting internal keys which also undergo substitution transformation by s-boxes. The s-boxes are designed on the principle that bent-function-based s-boxes possess good characteristics for encryption. The s-boxes of the invention are represented by (m.times.n) binary matrices.
Claims16
In a data encryption method of cryptographically transforming plaintext into ciphertext in data blocks of a predetermined bitlength comprising a plurality of consecutive transformation rounds of half of each data block, each consecutive transformation round comprising steps of:
- selecting an internal key of a specific bit combination from key bits;
- processing the internal key by a (m.times.n) substitution box to generate a modified internal key, where m and n are positive even integers, m<<n, and ##EQU8## XORing half of each data block with the modified internal key to generate a first modified half data block;
- processing the first modified half data block by a plurality of (m.times.n) mutually different substitution boxes to generate a second modified half data block;
- and
- XORing the second modified half data block with the remaining half of the data block to generate a transformed half data block of a transformation round.
In a data encryption method of cryptographically transforming plaintext into ciphertext in data blocks, each data block containing 2n bits, n being a positive even integer, comprising a plurality of consecutive transformation rounds, each consecutive transformation round comprising steps of:
- selecting an internal key of a specific bit combination and of s*m bits long from key bits, s being a positive integer and m being positive even integer;
- processing the internal key by s (m.times.n) mutually different substitution boxes to generate a modified internal key, where m<<n, and ##EQU9## XORing half of each data block with the modified internal key to generate a first modified half data block;
- dividing the first modified half data block into r parts, r being a positive integer;
- and
- processing each part of the first modified half data block by each of r (m.times.n) mutually different substitution boxes to generate a second modified half data block;
- and
- XORing the second modified half data block with the remaining half of the data block to generate a transformed half data block of a transformation round.
A data encryption system for cryptographically transforming plaintext into ciphertext in data blocks of a predetermined bitlength by performing a plurality of consecutive transformation rounds of half of each data block, comprising a plurality of partially bent-function-based (m.times.n) s-boxes where m and n are positive even integers, m<<n, ##EQU10## each (m.times.n) s-box being a 2.sup.m .times.n binary matrix which contains n binary bent vectors of length 2.sup.m and at least one non-zero linear combination of the vectors which is not bent;
- a key processor for processing an internal key by at least one of the s-boxes to generate a modified internal key;
- a data processor for processing each half data block by at least one of the s-boxes;
- and
- an XOR gate for XORing the modified internal key and the processed half data block to generate a transformed half data block of the transformation round.
Dependencies are inferred from the claim text.