A History of Cryptography - Introduction to Cryptography with Java Applets - page 4

RIVVJ JVEKZ RCCPV DGKPE FKSFI EEFKU VJKIF PVUEF KJKRZ EVUEF KGLIV
NZKYF LKCFJ JNZKY FLKXR ZEKYV IVWFI VZEVD GKZEV JJKYV IVZJE FWFID
EFJVE JRKZF EGVIT VGKZF EDVEK RCIVR TKZFE FITFE JTZFL JEVJJ EFVPV
VRIEF JVKFE XLVSF UPDZE UEFTF CFIJF LEUJD VCCKR JKVKF LTYFS AVTKF
WKYFL XYKEF JVVZE XREUJ FFEKF EFKYZ EBZEX EFZXE FIRET VREUE FVEUK
FZXEF IRETV EFFCU RXVRE UUVRK YEFVE UKFFC URXVR EUUVR KYEFR EXLZJ
YTRLJ VFWRE XLZJY TVJJR KZFEG RKYEF NZJUF DREUE FRKKR ZEDVE KJZET
VKYVI VZJEF KYZEX KFRKK RZEKY VSFUY ZJRKK MRCZM VJKYL JNZKY EFYZE
UIRET VFWDZ EUEFY ZEUIR ETVRE UYVET VEFWV RIWRI SVPFE UUVCL UVUKY
FLXYK IZXYK YVIVZ JEZIM RER
If we count the occurrences of each letter in the text, we come up with the following
counts:
A: 1 B: 1 C: 16 D: 14 E: 82 F: 69 G: 10 H: 0 I: 27 J: 47 K: 61 L: 15
M: 3 N: 5 O: 2 P: 8 Q: 0 R: 45 S: 5 T: 21 U: 28 V: 69 W: 9 X: 15
Y: 28 Z: 47
The letter E appears most frequently, but this would be the identity map, not a smart
choice. Otherwise, the most frequently occurring letters are F and V, which each appear 69
times. Thus, the shift value is likely to be
distance(E, F) = 1, or distance(E, V) = 17.
If we try the shift value of 1, we see that we get only garbage. If we shift each letter of
the ciphertext to the left by 17, though, we get the beautiful expression:
FORMI SEXAC TLYEM PTINE SSEMP TINES SEXAC TLYFO RMSOI TISWI THSEN
SATIO NPERC EPTIO NMENT ALREA CTION ANDCO NSCIO USNES SALLT HINGS
AREES SENTI ALLYE MPTYN OTBOR NNOTD ESTRO YEDNO TSTAI NEDNO TPURE
WITHO UTLOS SWITH OUTGA INTHE REFOR EINEM PTINE SSTHE REISN OFORM
NOSEN SATIO NPERC EPTIO NMENT ALREA CTION ORCON SCIOU SNESS NOEYE
EARNO SETON GUEBO DYMIN DNOCO LORSO UNDSM ELLTA STETO UCHOB JECTO
FTHOU GHTNO SEEIN GANDS OONTO NOTHI NKING NOIGN ORANC EANDN OENDT
OIGNO RANCE NOOLD AGEAN DDEAT HNOEN DTOOL DAGEA NDDEA THNOA NGUIS
HCAUS EOFAN GUISH CESSA TIONP ATHNO WISDO MANDN OATTA INMEN TSINC
ETHER EISNO THING TOATT AINTH EBODH ISATT VALIV ESTHU SWITH NOHIN
DRANC EOFMI NDNOH INDRA NCEAN DHENC ENOFE ARFAR BEYON DDELU DEDTH
OUGHT RIGHT HEREI SNIRV ANA
It is not necessary that a monoalphabetic mapping be based on a shift. We can map the
plaintext alphabet letters to a permutation of the alphabet, as shown in Table 1.4.
This particular mapping is based on a keyphrase “THE HILLS ARE ALIVE.” Note that
the first few letters in the ciphertext column are the initial occurrences of each letter in the
phrase. This was often done in practice, as it made the permutation easy to reconstruct.
However, a permutation certainly need not be based on such a keyphrase.