# The Special Fish Report

## Albert W. Small (December 1944)

### Page 101

Tony Sale's
Codes and Ciphers

| previous page | next page | index page |

CX/MSS
TOP SECRET Special Fish Report Page 101

therefore: 1/2(t+1)(t+1-1) + 1/2(4-t)(4-t -1) = T. The following table can

t T .

0 6
1 4
2 4
3 6
4 10

If at any given juxtaposition of the two tapes, we now make a count not only

of the 4-dot characters (as done in the crib run shown, for all juxtapositions)

but also of 3 dot 1 cross, 2 dot 2 cross, l dot 3 cross, and 0 dot 4 cross,

characters ("t" = 4, 3, 2, 1, 0) we can multiply such counts by the proper

T scores from the above table, and obtain the best possible scoring for

that particular given juxtaposition. This is easily done by setting the

tapes to the chosen juxtaposition, and making a "sixteen letter

count," and then grouping these letters into categories of "t," applying

the T values.

Since there are (1/2)*5*4*N or 10 N comparisons possible, the number

of dots expected at random is 5 N, and sigma is of course (2.5N)^1/2.

Thus after a crib run has been made as shown on page 98, a 16 letter count

is usually made at the juxtaposition suggested by the first run, the T score

computed, and resultant sigmage computed. If the resultant sigmage is above

that obtained from the original run, and is high (usually 5 sigma or better)

then the juxtaposition is accepted, and the key recovered from adding

crib and cipher together at that juxtaposition. In the present example

the sigmage from the 16 letter count (this count not shown) was 6.1 sigma,

so the setting was deemed proper.

| previous page | next page | index page |