TheCodeBreakers
Arne Beurling. During the bitter struggle of Finland against Russian
aggressors in the Winter War of 1939-1940, Sweden fed intelligence
based on cryptanalysis to her neighbor. Beurling attacked the top
system, the 5-digit strategic, which was actually a 4-digit code with an
extra digit added as some form of check. In several of the codes, the page
digit—the second— was repeated, so that the groups would look like
52217, 88824, and so on. In others, the fifth digit gave the unit total of
the preceding four digits, so that 6432 would have a check digit of 5,
making the codegroup 64325. Beurling wrote the cryptograms on a sheet
of graph paper with five-millimeter squares that was so large—about 3X4
feet —that he had to order it specially. He sought to strip the
superencipherment and, with luck, sometimes succeeded.
Soviet strategy against Finland called for a five-pronged invasion
along their north-south border
annaabi.ee 
