Method and apparatus for generating a cipher stream

A digital data stream generator for generating a cipher stream said digital data stream generator comprising:

• at least one linear feedback shift register (LFSR);
• a summing means for producing a sequence of sums of the outputs of said at least one LFSR;
• a non-linear feedback processing means for producing a sequence of non-linear values in accordance with the outputs of said at least one LFSR and at least one previous value of said non-linear output value sequence;
• and an output processing means for generating a data stream in accordance with a Bent function utilizing a plurality of pairs of said sequence of sums and at least one of said sequence of non-linear values, wherein the difference in the sequence position of the members of each pair is different as between each pair.

A method of encrypting a digital message, said method comprising the steps of:

• generating a pseudo random data stream sequence;
• performing a non-linear feedback transformation on said data stream sequence;
• generating a cipher stream in which correlations to linear forms are minimized by summing products of pairs of values of said data stream sequence with a value of said non-linear feedback transformation, the pairs of values being chosen such that the difference in sequence position as between each member of a pair is different as between each pair;
• and encrypting the digital message on the basis of said cipher stream.

A method of decrypting an encrypted digital message, said method comprising the steps of:

• generating a pseudo random data stream sequence;
• performing a non-linear feedback transformation on said data stream sequence;
• generating a cipher stream in which correlations to linear forms are minimized by summing products of pairs of values of said data stream sequence with a function based on a value of said non-linear feedback transformation, the pairs of values being chosen such that the difference in sequence position as between each member of a pair is different as between each pair;
• and decrypting the digital message on the basis of said cipher stream.

A method of generating a cipher stream utilizing a digital processing apparatus, said method comprising the steps of:

• generating a pseudo random number stream sequence m.sub.j ;
• generating a number stream sequence s.sub.j in accordance with a non-linear feedback scheme;
• and generating an output cipher stream sequence z.sub.j according to:
• ##EQU22## where c and d are predetermined integers with c<d.ltoreq.j and a.sub.k and b.sub.k are integers less than or equal to j such that (a.sub.c -b.sub.c).noteq.(a.sub.f -b.sub.f) for all e and f in the closed interval.