The details of the technique in the article seem to be lacking. There's a bit more on the Wikipedia:
> When she obtained any military intelligence, she encoded it for transmitting by knitting using one-time codes hidden on a piece of silk that she used to tie up her hair; she would translate them using Morse code equipment.
> When she obtained any military intelligence, she encoded it for transmitting by knitting using one-time codes hidden on a piece of silk that she used to tie up her hair; she would translate them using Morse code equipment.
https://en.wikipedia.org/wiki/Phyllis_Latour