In the begining there was the concept.

A pencil, a sheet of squared graph paper and a set of knot element symbols denoting the WE, the SP, the corners and the crossings, each designated by a leter.

Lay out the knot so that the flow of the cord through the knot can be followed, then recreate the line of the cod on the squared paper using only the designated symbols.

Mark up the graph columns and rows as you would a spreadsheet, then for each square with a part of the knot drawn in it, write down the cell coordinates and the letter for the knot element.  This string of cell coordinats and their contents is the cypher for the knot and may be sent to another person, along with the cypher code instructions for them to be able to reliably reproduce the diagram.

Agreeing a standardised set of symbols and a standardised way of recording the cell coordinates was all that was required to make this cypher usable.