Abstract: Method and device for enciphering data words of a word width of n bits, in particular data words to be written in a computer storage, wherein a product cipher circuit comprises alternately one from a plurality of permutation boxes with n inputs and n outputs and one from a plurality of substitution boxes with n inputs and n outputs, each of these boxes being under the control of a specific part of an m-bits key. In the product cipher circuit the data words are consecutively enciphered in whole and the enciphering device can be regarded as a delay line. The data words to be enciphered can be combined with coding words which depend on the specific sector of the computer storage, in particular a hard storage disk unit, where the data words are stored. The sector-specific coding words and/or the m-bits key can be combined with a key to be entered by a user.