1. A device for performing a product block cipher operation on a block of data bits under control of a set of cipher key bits comprising: first store means storing said block of data bits, first linear transformation means permuting said set of cipher key bits, means connected to said first store means duplicating predetermined ones of the data bits of said block of data bits to produce ann expanded block of data bits equal in number to the number of said permuted cipher key bits, means connected to said expansion means and said first linear transformation means carrying out a substitution transformation function in accordance with said expanded block of data bits and said permuted cipher key bits to produce a substitution set of bits equal in number to the number of bits in said block of data, and second linear transformation means connected to said substitution transformation means permuting said substitution set of bits whereby the combined transformation results in a product block cipher of said block of data bits.