158
were approximately 57 rows and 25 columns with 4 digits in each column. On the first two pages, the sequence of digits could be expressed in terms of the numbers 1-26, with a dot being placed either side of a single digit number. On subsequent pages the numbers 10-35 were used which fitted more conveniently into the columns (see Fig. 1). This was a good first indication that this really was a code and not mathematical tables.
Besalon 24/8 3027 14 10 342 ARTZ 1614739
DR3 102
GREENPRM
TOMERATAZOONIZER 197araren
香港仔店收容所
4831 763)
Fig. 1: A sample of the coded diary involving the numbers 10-35. Note the column containing four zeros on the last but one line.
Getting Started. A research career in bifurcation theory and chaos is not the best background for tackling a problem in cryptography. However, a code written over 50 years ago and in a prisoner of war camp could not be too sophisticated and, with a little help from a computer, should not be too difficult to crack even for a novice, or so I reasoned.
First stop was the University library and I was soon browsing through some old books on cryptography, learning the basic methods. A substitution cipher seemed an obvious method, in which each number represents a letter and it is simply a question of matching each number with the right letter.