A method includes receiving an input artefact and a set of shared parameters comprising a coding frame, one or more positioned elements, a travel path, and an initial position, and receiving an input artefact. The method includes initializing an output string and a head index and a tail index. The method includes traversing the travel path by, for each position: (i) determining whether the next position includes any positioned element; (ii) responsive to the next position not including any positioned element, filling the head index with a content character from the next position and incrementing the head index; (iii) responsive to next position including any positioned element, filling the tail index with a content character from the next position, and decrementing the tail index. The method includes setting said next position based on an attack position for the positioned element according to a variant of chess.