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194 CHAPTER 10. TRANSPOSITION CIPHERS
then fill down the E column with the next four,
S Q U A R E
D Y
K T
O G
E H
then the Q column with the next five, etc. This gives us
S Q U A R E
F R I D A Y
S T A K E T
O O L O N G
T O G E T H
E R E
From here we simply read off the message (ignoring the keyword): Fridays
take too long to get here.
(4) Decipher VOOGH KEBWN TEEDR FEERY KOWNY SIRED with keyword daily.
(5) Decipher ENMPK EAKWN TESUE VYEES SDAAN with keyword later. 6
⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄
There are two standard tricks to use with transposition. The first we’ve seen
before – the use of nulls. As with monoalphabetic substitution, nulls are simply
meaningless letters added to the plaintext before enciphering with the hope of
making the decrypter’s life more difficult. While nulls may appear anywhere,
we will restrict ourselves to putting nulls at the beginnings and endings of messages.
As we will see, nulls used in this way add only modestly to the security of
columnar transposition. More worthwhile is performing interrupted columnar
transposition in which certain spots are skipped during the enciphering
and deciphering process.
6 (3) YNVEO OASRA IIONR RTLDN ROYMM GEA. (4) A completely filled rectangle with 6 rows:
Everybody’s working for the weekend. (5) The te and nns are nulls: Seven days make up
a week.