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Section E.2 Transposition Analysis

Consider this exercise from Exercises 4.4:

Decrypt this transposition cipher with crib WEATHER:

HIPYEN TAUTCI WSDWPF ETTEEA ARONRN ENPMNC RTEPTH
RERHR  EMTCA  PPHHI  OREOL  FAIEL  TETCA  RNRNF OSIAN
MYWRR  RTNIU  CEDNN  ASIAO  RLSFA  IITHU  TDENA HASOD
HYAEQ  RNTUA  FETRE  TTENR  RITDO  YHNDT  IMOER
Answer
weather report for march thirty first
rain temps nearly steady in the mid to
upper thirties winds e at ten to twenty
mph chance of rain one hundred percent
rain fall around a quarter of an inch

To crack the cipher you need to first transpose each block of characters into a vertical column.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
1 H T W E A E R R E  P  O  F  T  R  O  M  R  C  A  R  I  T  H  H  R  F  T  R  Y  I
2 I A S T R N T E M  P  R  A  E  N  S  Y  T  E  S  L  I  D  A  Y  N  E  T  I  H  M
3 P U D T O P E R T  H  E  I  T  R  I  W  N  D  I  S  T  E  S  A  T  T  E  T  N  O
4 Y T W E N M P H C  H  O  E  C  N  A  R  I  N  A  F  H  N  O  E  U  R  N  D  D  E
5 E C P E R N T R A  I  L  L  A  F  N  R  U  N  O  A  U  A  D  Q  A  E  R  O  T  R
6 N I F A N C H

Next we need to identify words in the text which are jumbled up like an anagram. Since we were given the crib WEATHER our task will be easier. In the first row columns 3, 4, 5, 2, 1, 6, 7 can spell out weather.

0 3 4 5 2 1 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
1 W E A T H E R R E  P  O  F  T  R  O  M  R  C  A  R  I  T  H  H  R  F  T  R  Y  I
2 S T R A I N T E M  P  R  A  E  N  S  Y  T  E  S  L  I  D  A  Y  N  E  T  I  H  M
3 D T O U P P E R T  H  E  I  T  R  I  W  N  D  I  S  T  E  S  A  T  T  E  T  N  O
4 W E N T Y M P H C  H  O  E  C  N  A  R  I  N  A  F  H  N  O  E  U  R  N  D  D  E
5 P E R C E N T R A  I  L  L  A  F  N  R  U  N  O  A  U  A  D  Q  A  E  R  O  T  R
6 F A N I N C H

Then if we take columns 8, 9, 10, 11, 14, 13 we get the word report. And, after making that change we can see than 12, 15, 20 spells for.

0 3 4 5 2 1 6 7 8 9 10 11 14 13 12 15 17 16 18 19 20 21 22 23 24 25 26 27 28 29 30
1 W E A T H E R R E  P  O  R  T  F  O  R  M  C  A  R  I  T  H  H  R  F  T  R  Y  I
2 S T R A I N T E M  P  R  N  E  A  S  T  Y  E  S  L  I  D  A  Y  N  E  T  I  H  M
3 D T O U P P E R T  H  E  R  T  I  I  N  W  D  I  S  T  E  S  A  T  T  E  T  N  O
4 W E N T Y M P H C  H  O  N  C  E  A  I  R  N  A  F  H  N  O  E  U  R  N  D  D  E
5 P E R C E N T R A  I  L  F  A  L  N  U  R  N  O  A  U  A  D  Q  A  E  R  O  T  R
6 F A N I N C H

It would make since for the next few words to be a date and if we arrange the columns as 16, 19, 20, 18, 23, 22, 24, 21, 25, 27, 29, 26, 30, 28 then we get march thirty first.

0 3 4 5 2 1 6 7 8 9 10 11 14 13 12 15 17 16 19 20 18 23 22 24 21 25 27 29 26 30 28
1 W E A T H E R R E  P  O  R  T  F  O  R  M  A  R  C  H  T  H  I  R  T  Y  F  I  R
2 S T R A I N T E M  P  R  N  E  A  S  T  Y  S  L  E  A  D  Y  I  N  T  H  E  M  I
3 D T O U P P E R T  H  E  R  T  I  I  N  W  I  S  D  S  E  A  T  T  E  N  T  O  T
4 W E N T Y M P H C  H  O  N  C  E  A  I  R  A  F  N  O  N  E  H  U  N  D  R  E  D
5 P E R C E N T R A  I  L  F  A  L  N  U  R  O  A  N  D  A  Q  U  A  R  T  E  R  O
6 F A N I N C H

Now the first row looks good, but the others are a little off. After some inspection you should see that swapping columns 11 and 15, and columns 17 and 20 should fix that.

0 3 4 5 2 1 6 7 8 9 10 15 14 13 12 11 20 16 19 17 18 23 22 24 21 25 27 29 26 30 28
1 W E A T H E R R E  P  O  R  T  F  O  R  M  A  R  C  H  T  H  I  R  T  Y  F  I  R
2 S T R A I N T E M  P  S  N  E  A  R  L  Y  S  T  E  A  D  Y  I  N  T  H  E  M  I
3 D T O U P P E R T  H  I  R  T  I  E  S  W  I  N  D  S  E  A  T  T  E  N  T  O  T
4 W E N T Y M P H C  H  A  N  C  E  O  F  R  A  I  N  O  N  E  H  U  N  D  R  E  D
5 P E R C E N T R A  I  N  F  A  L  L  A  R  O  U  N  D  A  Q  U  A  R  T  E  R  O
6 F A N I N C H

Which, with a little work, gives:

weather report for march thirty first
rain temps nearly steady in the mid to
upper thirties winds e at ten to twenty
mph chance of rain one hundred percent
rain fall around a quarter of an inch

Along the way this is the sort of scrap work you will produce.

Figure E.2.2. Sample Transposition Analysis: