In a recent press interview, a former terrorist of the 1970s described the cipher his group used to communicate. He claimed that method was unbreakable and I wonder if cryptographers today would agree. Here is how it functionned:
Take two identical books (same edition): one for the sender, one for the recipient.
Each sign - one could include spaces between words as signs - is encoded as follows:
(page number) (line number) (number of character on the line) (random number)
- additions, subtractions, multiplications or divisions of certain agreed value in a certain order are then applied. For example, 357 could mean:
(page number*3) (line number -5) (character number +7)
- This means that negative values can be created, especially if the substraction value is in the double digits
A software script for such a cipher would be I think relatively easy to design. Also, the agreed values of the operations in step 2 can be changed anytime so the same base text can be reused.
Bottom line, it means for example a single 7-letter word would produce a string of 28 numbers, of various lenghts and some negative values or decimals or fractions perhaps - depending on what values are used for the operations.
what is your opinion on this method?