Cryptography Reference
In-Depth Information
3 LSXCCAQ
4 TUGQQFC
5 ZQORRHF
6 ICUTTDZ
7 VZLCCEG
8 ZSCOOVD
9 NCBAAHL
10APSEEKQ
The position
VIWSHQTLUFTWDTZ
CHIFFRE
of the probable word supplies no coincidence (no two superimposed characters
are equal), which means that it is theoretically no option. We place the pertaining
ciphertext fragment, VIWSHQT, on top of the 10
×
7 matrix above. Only the 'V'
from the first position can be found in the next column (disk 7); the other characters
are not in the first generatrix in any other disk. This completes that word position
for this generatrix.
The word CHIFFRE is now moved forward and, excluding all positions, we look
at the next generatrix until we find a ciphertext fragment in which each ciphertext
character happens to be in one of the lower columns at least once. Another exclusion
condition is that the ciphertext characters must occur in
different
matrix rows. (If
there are multiple occurrences in one column, then we should be able to make the
choice so that this condition is met.)
We can now mount a plaintext attack on all positions found.
Figure 3.8:
(
continued
)
The method fails when the permuted alphabets on the disks form a Latin square,
i.e., when the disks have turning positions that cause each letter to occur at
least once in every row.
It is very unlikely that people still use ciphering cylinders today, and nobody
implements them in software. So why dedicate a full section to the Viaris
method, which is especially tailored to these devices? For a couple of reasons.
First, because of the comment on Latin squares in the paragraph above: when
you run cryptanalysis yourself, you will begin to understand why this disk
property is so important for cryptanalysis. This still doesn't mean that we are
able to design secure algorithms: we simply don't know what methods have
been or will be used by all the cryptanalysts in the world.
