Method of encipherment by permutations of fixed-length sequences

A method of enciphering information constituted by a finite sequence {S1,S2, . . . ,SN} of N symbols {S1,S2, . . . ,SN} selected from an alphabet A, wherein there are defined both a secret convention (K) of p key symbols K1, . . . ,Kp selected from a second alphabet B, and a multivariate function M having m+1 variables (m<=N):

• M(Xi1, . . . ,Xim,Y) operating Am×B in A, {i1, . . . , im} being m distinct indices in the range [1 ,N] and the function M being bijective relative to at least one (Xi1) of the m variables of A, said enciphering method comprising:
• initially placing the N symbols S1,S2, . . . ,SN) constituting the information to be enciphered in the N positions of a shift register, and then
• performing a succession of X turns of the shift register implementing a succession of X permutations on the sequences {S1,S2, . . . ,SN} such that where {S1,S2, . . . ,SN} is the sequence prior to the jth permutation, the sequence after the jth permutation is {S2,S3, . . . ,SN,Zj}, where Zj is equal to M(Si1, . . . ,Sim,Kj), the enciphered information being constituted by the sequence {S′1,S′2, . . . ,S′N} contained in the shift register at the end of the Xth permutation resulting from the Xth turn of the shift registers,
• wherein the number X of permutations is greater than several times the length N of the sequences {S1,S2, . . . ,SN},
• wherein the number m is equal to 3, the function M being defined by M(X1,X2,XN,Y), and
• wherein the function M(X1,X2,XN,Y) is calculated using the following steps:
• U=t1(X1,XN)
• V=t2(U,Y)
• Z=t1(V,X2)
• t1 and t2 being the functions associated with two Latin squares T1 and T2 of size equal to the number N.