Method and system for encryption with bidirectional difference propagation

A system configured to encrypt digital data, said data being divided into a sequence of N first blocks of a same length of n bits each, N being an integer greater than 1, n being an integer greater than 1, comprising:

• a) a pre-processing module comprising a processor, registers, an arithmetic module, and a memory containing a set including N invertible elements, the N first blocks and the N invertible elements being within a predetermined finite ring, the arithmetic module including multiplier modules, addition modules and inverter modules, the pre-processing module being adapted to receive the sequence of N blocks at an input, the arithmetic module being configured to determine N resulting blocks based on the N first blocks and the N invertible elements by executing the following resulting block determination operations,
• i) set YN=mN*XN, and
• ii) for i=N−1 to 1, set Yi=(mi*Xi)+Yi+1,
• wherein ‘i’ is an index, Y1-YN are the N resulting blocks, respectively, m1-mN are the N invertible elements, respectively, and X1-XN are the N first blocks, respectively, and
• wherein the pre-processing module is configured to output a sequence of the N resulting blocks, each of the N resulting blocks having a length identical to a corresponding block of the input sequence of N first blocks;
• and
• b) a ciphering module configured to cipher each of the sequence of the N resulting blocks with a block cipher in a chaining mode from the first block of the sequence of the N resulting blocks to the last block of the sequence of the N resulting blocks with a ciphering algorithm and to produce a sequence of N encrypted blocks, said encrypted blocks having each a same length.