TheCodeBreakers
One way in which the Okhrana, the
notorious secret police, kept tabs on underground workers was to have
the black
chambers read the letters and telegrams of suspects—as well as most
foreign mail and a random selection of the domestic post, too.
The most popular cipher of the Russian underground seems to have
derived from the prisons in which so many of its leaders had to serve
time. Intercommunication among the inmates was strictly forbidden. But
the prisoners, languishing in the tomblike solitude of their gloomy stone
casements, with nothing to occupy their minds, had the patience,
perseverance, and ingenuity to outwit their jailers. They knocked, using
the number of taps to indicate the rows and columns of a simple
checkerboard, like the original Polybius square, sometimes 6 X 6 to
accommodate the 35 letters of the old Russian alphabet, more often five
across and six down, with the alternate letter forms eliminated. In
English, the checkerboard would take this form:
annaabi.ee 
