Cryptology - Unofficial St. Mary's College of California Web Site

6.2. DECRYPTING MONOALPHABETIC CIPHERS 95
At this point it is nearly fill in the blanks. (This is the opening sentence of
Colonel Parker Hitt’s 1916 Manual for the Solution of Military Ciphers, one
of the first serious American books on cryptology, enciphered with a keyword
transposed cipher with keyword TRICKY.)
⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄
Not all examples will be as quick as this one. You will often need to swap
a pair of common letters, like we did from K=r to K=s. However, work methodically,
on a large piece of paper, with pencil and not ink, and after a little
practice soon you will be decrypting ciphers with the best of them.
Example: Decrypt the following cipher without word breaks.
ROXEY ZLOHE QXHUW ROXEY HUHKX TVTHO BTZPB
YVPBT RHKKB WYNVU ZOOBR VEOZR HKTRV BURBT
HUWVU GDURY VZUYQ BXVUW BBWPV OOZOZ UBHUZ
YQBON QHYZU BWZBT YQBZY QBODU WZBTY QBVOU
HYDOB TQZNB IBOWV GGBOG DUWHP BUYHK KXROX
EYZLO HEQXV TYQBZ OBYVR HKHUW HMTYO HRYRO
XEYHU HKXTV TVTBP EVOVR HKHUW RZURO BYBWH
IVWFH QU
Step 1) Frequency Chart:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
0 28 0 4 8 1 4 24 2 0 9 2 1 3 23 5 11 15 0 14 21 18 13 10 20 16
Step 2) Certainly this is not any sort of Shift Cipher.
Step 3) The most common letters are B, H, O, R, T, U, V, Y, and Z.
Step 4) See Figure 6.3.
Step 5) See Figure 6.4.
Step 6) The lack of information about initial and final letters make this cipher
considerably more difficult to decrypt than the previous one. But we must start
somewhere. B is most common letter, has lots of mates, is doubled, so maybe
B=e. If this is so, the most common mates with B are OTUWYZ, so these may be
consonants and HRV vowels.
Looking at HRV, HV both have many low frequency mates, whereas R combines
with mostly high frequency letters. So HV must indeed be vowels, but R is
actually probably a consonant.
Now V appears both before and after B=e, whereas H appears only after.
Let’s guess V=i. The pair eo is very rare, so if H is to be a vowel it must be a.