D'Agapeyeff Cipher As Two 7x7 Squares

Picking up where I left off last time, I want to continue testing the D'Agapeyeff cipher as a combination substitution-transposition cipher with nulls added to the final ciphertext.


As stated in the previous post, removing all the 6s, 7s, 8s, 9s and the zeros would leave 196 numbers or 98 number pairs.

Before:

75628 28591 62916 48164 91748 58464 74748 28483 81638 18174

74826 26475 83828 49175 74658 37575 75936 36565 81638 17585

75756 46282 92857 46382 75748 38165 81848 56485 64858 56382

72628 36281 81728 16463 75828 16483 63828 58163 63630 47481

91918 46385 84656 48565 62946 26285 91859 17491 72756 46575

71658 36264 74818 28462 82649 18193 65626 48484 91838 57491

81657 27483 83858 28364 62726 26562 83759 27263 82827 27283

82858 47582 81837 28462 82837 58164 75748 58162 92000

After:

    52 251 21 414 14 544 44 243 13 114
    42 245 32 415 45 355 53 355 13 155
    55 422 25 432 54 315 14 545 45 532
    22 321 12 143 52 143 32 513 33 441
    11 435 45 455 24 225 15 141 25 455
    15 324 41 242 24 113 52 444 13 541
    15 243 35 234 22 252 35 223 22 223
    25 452 13 242 23 514 54 512 2

The question now becomes, how were these numbers written prior becoming the final ciphertext?  And why was there a zero near the middle?

Some ideas:

1. The numbers are paired moving left to right, top to bottom (first pair 52).  The zero would mark the 49th pair, splitting the ciphertext into two sets of 49 pairs.  Or possibly two 7x7 squares.
2. The numbers are paired using the first number (5) and the first number after the middle zero, the 99th overall number (4).  This would yield 98 total number pairs.
3. The numbers were no longer paired when placed into 14x14 transposition table or two 7x14 tables.  They were fractionated much like the example on pg. 124-125 of the original D'Agapeyeff book.  Shown below.

The thing that steers me away from the use of a 14x14 table in both the conventional setup (no nulls used) and the setup I'm proposing is D'Agapeyeff's use of a keyword to reorder the columns.  Choosing a 14+ letter keyword doesn't seem as plausible, nor did D'Agapeyeff use a longer key phrase in any of his examples in the book.  You can't rule it out completely, but it seems less plausible.  It would seem to make sense that he was building off his own examples since this was included at the end of the book, asking the reader to test the skills they had just learned.

In the next post I'll post results from the phi tests I ran on the 7x7 squares of pairs of numbers.