Abstract: A method of generating a substitution box (S-box) involves generating an S-box with desired characteristics, forming a new S-box with another column such that the new S-box has the desired characteristics as well, and continuing to add columns in these ways until the S-box has the proper size.

Abstract: A method of encrypting or decrypting an input message block of binary data of predetermined length 2n into an output message block by dividing the message block into two equal size halves, performing one or more transformation rounds on the message block halves, each transformation round further comprising the steps of determining a key, processing the first half data block using a hash function to obtain a modified first half data block of length n, and combining the modified first half data block with the second half data block to obtain a modified second half data block of length n; and, lastly, appending the first modified half data block to the second modified half data block to obtain the output message block.

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.