How to decode a Vigenere code
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Apr 16, 2021
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About This Presentation
An interesting presentation on coding and decoding for secondary school students.
Slide Content
Prepared by D Almeida
School of Mathematics and Statistics (SoMaS)
Vigenère ciphers
School of Mathematics and Statistics (SoMaS)
Vigenère ciphers
Prepared by D Almeida
What is a Vigenère cipher?
•Consider this sentence:-
•Mathematics is the engine of all science. It enables physical phenomena to
be modelled in a structured way. The model enables scientists to make
predictions about the phenomena.
•In a Vigenèrecipher a key word (generally larger than 3 letters) is used to
scramble a message. We will use the key word surd.
•The word surd is repeated above the given message (with no spaces) thus:
•surdsurdsurdsurdsurdsurdsurdsurdsurdsurdsurdsurdsurdsurdsur
•MathematicsistheengineofallscienceItenablesphysicalphenomenato
What is a Vigenère cipher?
•Consider this sentence:-
•Mathematics is the engine of all science. It enables physical phenomena to
be modelled in a structured way. The model enables scientists to make
predictions about the phenomena.
•In a Vigenèrecipher a key word (generally larger than 3 letters) is used to
scramble a message. We will use the key word surd.
•The word surd is repeated above the given message (with no spaces) thus:
•surdsurdsurdsurdsurdsurdsurdsurdsurdsurdsurdsurdsurdsurdsur
•MathematicsistheengineofallscienceItenablesphysicalphenomenato
Prepared by D Almeida
What is a Vigenère cipher?
The key surddefines by how much each letter in the message is translated.
This means a Vigenère code is variable Caesar code.
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
1BCDEFGHIJKLMNOPQRSTUVWXYZA
2CDEFGHIJKLMNOPQRSTUVWXYZAB
3DEFGHIJKLMNOPQRSTUVWXYZABC
4EFGHIJKLMNOPQRSTUVWXYZABCD
5FGHIJKLMNOPQRSTUVWXYZABCDE
6GHIJKLMNOPQRSTUVWXYZABCDEF
7HIJKLMNOPQRSTUVWXYZABCDEFG
8IJKLMNOPQRSTUVWXYZABCDEFGH
9JKLMNOPQRSTUVWXYZABCDEFGHI
10KLMNOPQRSTUVWXYZABCDEFGHIJ
11LMNOPQRSTUVWXYZABCDEFGHIJK
12MNOPQRSTUVWXYZABCDEFGHIJKL
13NOPQRSTUVWXYZABCDEFGHIJKLM
14OPQRSTUVWXYZABCDEFGHIJKLMN
15PQRSTUVWXYZABCDEFGHIJKLMNO
16QRSTUVWXYZABCDEFGHIJKLMNOP
17RSTUVWXYZABCDEFGHIJKLMNOPQ
18STUVWXYZABCDEFGHIJKLMNOPQR
19TUVWXYZABCDEFGHIJKLMNOPQRS
20UVWXYZABCDEFGHIJKLMNOPQRST
21VWXYZABCDEFGHIJKLMNOPQRSTU
22WXYZABCDEFGHIJKLMNOPQRSTUV
23XYZABCDEFGHIJKLMNOPQRSTUVW
24YZABCDEFGHIJKLMNOPQRSTUVWX
25ZABCDEFGHIJKLMNOPQRSTUVWXY
This table tells us that
A letter corresponding to Dis translated by 3:
e.g. A D, B E, C F, …
A letter corresponding to Ris translated by 17:
e.g. A R, B S, C T, …
A letter corresponding to Sis translated by 18:
e.g. A S, B T, C U, …
A letter corresponding to Uis translated by 20:
e.g. A U, B V, C W, …
According to these rules our message becomes
the last line below:
surd surd surd surd surd surd surd surd surd surd surd surd surd surd surd su
math emat icsi sthe engi neof alls cien ceit enab lesp hysi calp heno mena to
eukk wgrw awjl knyh whxl fyfi sfcv ucvq uyzw whre dyjs zsjl uucs zyer eyed li
The rules for translation are given by this table
m corresponds
to s, so it is
translated by
18to e
What is a Vigenère cipher?
The key surddefines by how much each letter in the message is translated.
This means a Vigenère code is variable Caesar code.
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
1BCDEFGHIJKLMNOPQRSTUVWXYZA
2CDEFGHIJKLMNOPQRSTUVWXYZAB
3DEFGHIJKLMNOPQRSTUVWXYZABC
4EFGHIJKLMNOPQRSTUVWXYZABCD
5FGHIJKLMNOPQRSTUVWXYZABCDE
6GHIJKLMNOPQRSTUVWXYZABCDEF
7HIJKLMNOPQRSTUVWXYZABCDEFG
8IJKLMNOPQRSTUVWXYZABCDEFGH
9JKLMNOPQRSTUVWXYZABCDEFGHI
10KLMNOPQRSTUVWXYZABCDEFGHIJ
11LMNOPQRSTUVWXYZABCDEFGHIJK
12MNOPQRSTUVWXYZABCDEFGHIJKL
13NOPQRSTUVWXYZABCDEFGHIJKLM
14OPQRSTUVWXYZABCDEFGHIJKLMN
15PQRSTUVWXYZABCDEFGHIJKLMNO
16QRSTUVWXYZABCDEFGHIJKLMNOP
17RSTUVWXYZABCDEFGHIJKLMNOPQ
18STUVWXYZABCDEFGHIJKLMNOPQR
19TUVWXYZABCDEFGHIJKLMNOPQRS
20UVWXYZABCDEFGHIJKLMNOPQRST
21VWXYZABCDEFGHIJKLMNOPQRSTU
22WXYZABCDEFGHIJKLMNOPQRSTUV
23XYZABCDEFGHIJKLMNOPQRSTUVW
24YZABCDEFGHIJKLMNOPQRSTUVWX
25ZABCDEFGHIJKLMNOPQRSTUVWXY
This table tells us that
A letter corresponding to Dis translated by 3:
e.g. A D, B E, C F, …
A letter corresponding to Ris translated by 17:
e.g. A R, B S, C T, …
A letter corresponding to Sis translated by 18:
e.g. A S, B T, C U, …
A letter corresponding to Uis translated by 20:
e.g. A U, B V, C W, …
According to these rules our message becomes
the last line below:
surd surd surd surd surd surd surd surd surd surd surd surd surd surd surd su
math emat icsi sthe engi neof alls cien ceit enab lesp hysi calp heno mena to
eukk wgrw awjl knyh whxl fyfi sfcv ucvq uyzw whre dyjs zsjl uucs zyer eyed li
The rules for translation are given by this table
m corresponds
to s, so it is
translated by
18to e
Prepared by D Almeida
Objective
We will break this Vigenerecipher presented in blocks of 5 letters:
ANYVG YSTYN RPLWH RDTKX RNYPV QTGHP HZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUA YYMGE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVG YS
The key aim is to find how many letters were used in the key word used to code
the original message.
This does not mean the key word has 5 letters!
Objective
We will break this Vigenerecipher presented in blocks of 5 letters:
ANYVG YSTYN RPLWH RDTKX RNYPV QTGHP HZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUA YYMGE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVG YS
The key aim is to find how many letters were used in the key word used to code
the original message.
This does not mean the key word has 5 letters!
Prepared by D Almeida
1. Find repeating blocks of groups of three or more letters
2. Find the gaps nbetween repeating blocks of groups of letters
3. Find the non-trivial factors of n(so exclude 1 and n)
4. We must find the common factor (larger than 3) with the highest frequency.
Call this N
5. Group the ciphered text in blocks of N letters.
6. Find the frequencies of the 26 letters a, b, c,….., x, y, zin the first place in each
block; repeat for the second place, third place, ….N
th
place
7. Compare the frequencies of the 26 letters a, b, c,….., x, y, zin the first place with
the expected frequencies of the 26 letters: observationand judgementwill imply a
Caesar shift of the letters. Replace the ciphered letter in each of the first places
with the uncipheredone. Repeat for other places, etc. using common sense and
comparative frequencies for the other places.
8. Partition to reveal message.
The key steps in cracking such ciphers is given below and the steps will
be illustrated by applying it to our ciphered text:
Generally the key word will have more than 3 letters but for practice identifying blocks we include 3
1. Find repeating blocks of groups of three or more letters
2. Find the gaps nbetween repeating blocks of groups of letters
3. Find the non-trivial factors of n(so exclude 1 and n)
4. We must find the common factor (larger than 3) with the highest frequency.
Call this N
5. Group the ciphered text in blocks of N letters.
6. Find the frequencies of the 26 letters a, b, c,….., x, y, zin the first place in each
block; repeat for the second place, third place, ….N
th
place
7. Compare the frequencies of the 26 letters a, b, c,….., x, y, zin the first place with
the expected frequencies of the 26 letters: observationand judgementwill imply a
Caesar shift of the letters. Replace the ciphered letter in each of the first places
with the uncipheredone. Repeat for other places, etc. using common sense and
comparative frequencies for the other places.
8. Partition to reveal message.
The key steps in cracking such ciphers is given below and the steps will
be illustrated by applying it to our ciphered text:
Generally the key word will have more than 3 letters but for practice identifying blocks we include 3
Prepared by D Almeida
Step 1. Finding repeating blocks of groups of 3 or more
letters.
Use MS Word ‘find’ to highlight the letters A, B, ….
ANYVG YSTYN RPLWHRDTKX RNYPV QTGHP HZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRW AGEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUAYYMGE EMJQK SFCGU GYBPJ BPZYP J ASNN
FSTUS STYVG YS
There are no repeating groups of 3 or more letters beginning with A.
So we keep going.
Step 1. Finding repeating blocks of groups of 3 or more
letters.
Use MS Word ‘find’ to highlight the letters A, B, ….
ANYVG YSTYN RPLWHRDTKX RNYPV QTGHP HZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRW AGEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUAYYMGE EMJQK SFCGU GYBPJ BPZYP J ASNN
FSTUS STYVG YS
There are no repeating groups of 3 or more letters beginning with A.
So we keep going.
Prepared by D Almeida
Step 1 (continued) Finding repeating blocks of groups
of 3 or more letters.
Use MS Word ‘find’ to highlight the letters A, B, ….
ANYVGYSTYN RPLWHRDTKX RNYPV QTGHP HZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SX GOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMT G
AYVIY GHPEM YFARW AOAEL UPIUA YYM GE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVGYS
By (careful) observationwe identify the groups GHP and GEE.
Step 1 (continued) Finding repeating blocks of groups
of 3 or more letters.
Use MS Word ‘find’ to highlight the letters A, B, ….
ANYVGYSTYN RPLWHRDTKX RNYPV QTGHP HZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SX GOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMT G
AYVIY GHPEM YFARW AOAEL UPIUA YYM GE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVGYS
By (careful) observationwe identify the groups GHP and GEE.
Prepared by D Almeida
Step 1 (continued) Finding repeating blocks of groups
of 3 or more letters.
The groups GHPand GEE:
ANYVG YSTYN RPLWHRDTKX RNYPV QTGHPHZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUA YYM GE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVG YS
And here’s the group LEEBMMTG :
ANYVG YSTYN RPLWH RDTKX RNYPV QTGHP HZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGN LE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JM LEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUA YYMGE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVG YS
Step 1 (continued) Finding repeating blocks of groups
of 3 or more letters.
The groups GHPand GEE:
ANYVG YSTYN RPLWHRDTKX RNYPV QTGHPHZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUA YYM GE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVG YS
And here’s the group LEEBMMTG :
ANYVG YSTYN RPLWH RDTKX RNYPV QTGHP HZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGN LE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JM LEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUA YYMGE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVG YS
Prepared by D Almeida
Step 2 Finding the gaps nbetween repeating blocks of
groups of letters
ANYVG YSTYN RPLWHRDTKX RNYPV QTGHPHZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUA YYM GE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVG YS
By (careful) counting the gap between the two GHP’s = 198
and the gap between the two GEE’s = 108
Important: the gap between the AMB’sin:
AMBCV GUYPG LPRCT MAMBD is 16 (count between the A’sand add 1)
15
15+ 1
Step 2 Finding the gaps nbetween repeating blocks of
groups of letters
ANYVG YSTYN RPLWHRDTKX RNYPV QTGHPHZKFE YUMUS AYWVK ZYEZM EZUDL
JKTUL JLKQB JUQVU ECKBN RCTHP KESXM AZOEN SXGOL PGNLE EBMMT GCSSV
MRSEZ MXHLP KJEJH TUPZU EDWKN NNRWA GEEXS LKZUD LJKFI XHTKP IAZMX
FACWC TQIDU WBRRL TTKVN AJWVB REAWT NSEZM OECSS VMRSL JMLEE BMMTG
AYVIY GHPEM YFARW AOAEL UPIUA YYM GE EMJQK SFCGU GYBPJ BPZYP JASNN
FSTUS STYVG YS
By (careful) counting the gap between the two GHP’s = 198
and the gap between the two GEE’s = 108
Important: the gap between the AMB’sin:
AMBCV GUYPG LPRCT MAMBD is 16 (count between the A’sand add 1)
15
15+ 1
Prepared by D Almeida
Step 3 Finding the non-trivial factors of nexclude 1 and n)
After examining the repeating groups of letters we will have this table:
Group Gap Factors
GHP 198 2, 3, 6, 9, 11, 18, 22, 33, 66, 99
GEE 108 2, 3, 4, 6, 9, 12, 18, 27, 36, 54
LEEBMMTG 114 2, 3, 6, 19, 38, 57
SEZM 84 2, 3, 4, 6, 7, 12, 14, 21, 28, 42
STY 274 1, 2, 137, 274
YVGYS 280 2, 4, 5, 7, 8, 10, 14, 20, 28, 35,
40, 56, 70, 140
ZMX 48 2, 3, 4, 6, 8, 12, 16, 24
ZUDLJK 96 2, 3, 4, 6, 8, 12, 16, 24, 32, 48
Step 3 Finding the non-trivial factors of nexclude 1 and n)
After examining the repeating groups of letters we will have this table:
Group Gap Factors
GHP 198 2, 3, 6, 9, 11, 18, 22, 33, 66, 99
GEE 108 2, 3, 4, 6, 9, 12, 18, 27, 36, 54
LEEBMMTG 114 2, 3, 6, 19, 38, 57
SEZM 84 2, 3, 4, 6, 7, 12, 14, 21, 28, 42
STY 274 1, 2, 137, 274
YVGYS 280 2, 4, 5, 7, 8, 10, 14, 20, 28, 35,
40, 56, 70, 140
ZMX 48 2, 3, 4, 6, 8, 12, 16, 24
ZUDLJK 96 2, 3, 4, 6, 8, 12, 16, 24, 32, 48
Prepared by D Almeida
Step 4 Finding the common factor N (larger than 3) with the
highest frequency.
So N = 6
Factor > 3 Frequency
4 5
6 6
7, 8, 9, 14, 16 2
12 4
Others 1
Highest frequency
Step 4 Finding the common factor N (larger than 3) with the
highest frequency.
So N = 6
Factor > 3 Frequency
4 5
6 6
7, 8, 9, 14, 16 2
12 4
Others 1
Highest frequency
Prepared by D Almeida
Step 5 Group the ciphered text in blocks of N = 6letters.
ANYVGY STYNRP LWHRDT KXRNYP VQTGHP HZKFEY UMUSAY WVKZYE
ZMEZUD LJKTUL JLKQBJ UQVUEC KBNRCT HPKESX MAZOEN SXGOLP
GNLEEB MMTGCS SVMRSE ZMXHLP KJEJHT UPZUED WKNNNR WAGEEX
SLKZUD LJKFIX HTKPIA ZMXFAC WCTQID UWBRRL TTKVNA JWVBRE
AWTNSE ZMOECS SVMRSL JMLEEB MMTGAY VIYGHP EMYFAR WAOAEL
UPIUAY YMGEEM JQKSFC GUGYBP JBPZYP JASNNF STUSST YVGYS
Step 5 Group the ciphered text in blocks of N = 6letters.
ANYVGY STYNRP LWHRDT KXRNYP VQTGHP HZKFEY UMUSAY WVKZYE
ZMEZUD LJKTUL JLKQBJ UQVUEC KBNRCT HPKESX MAZOEN SXGOLP
GNLEEB MMTGCS SVMRSE ZMXHLP KJEJHT UPZUED WKNNNR WAGEEX
SLKZUD LJKFIX HTKPIA ZMXFAC WCTQID UWBRRL TTKVNA JWVBRE
AWTNSE ZMOECS SVMRSL JMLEEB MMTGAY VIYGHP EMYFAR WAOAEL
UPIUAY YMGEEM JQKSFC GUGYBP JBPZYP JASNNF STUSST YVGYS
Prepared by D Almeida
Step 6 Find the frequencies of the 26 letters a, b, c,….., x, y, zin
the first place in each block;
The first place letters:
ANYVGY STYNRP LWHRDT KXRNYP VQTGHP HZKFEY UMUSAY WVKZYE
ZMEZUD LJKTUL JLKQBJ UQVUEC KBNRCT HPKESX MAZOEN SXGOLP
GNLEEB MMTGCS SVMRSE ZMXHLP KJEJHT UPZUED WKNNNR WAGEEX
SLKZUD LJKFIX HTKPIA ZMXFAC WCTQID UWBRRL TTKVNA JWVBRE
AWTNSE ZMOECS SVMRSL JMLEEB MMTGAY VIYGHPEMYFAR WAOAEL
UPIUAY YMGEEM JQKSFC GUGYBP JBPZYP JASNNF STUSST YVGYS
Frequency table:
A B C D E F G H I J K L M
2 0 0 0 1 0 2 3 0 6 3 3 3
N O P Q R S T U V W X Y Z
0 0 0 0 0 6 1 5 2 5 0 2 4
Step 6 Find the frequencies of the 26 letters a, b, c,….., x, y, zin
the first place in each block;
The first place letters:
ANYVGY STYNRP LWHRDT KXRNYP VQTGHP HZKFEY UMUSAY WVKZYE
ZMEZUD LJKTUL JLKQBJ UQVUEC KBNRCT HPKESX MAZOEN SXGOLP
GNLEEB MMTGCS SVMRSE ZMXHLP KJEJHT UPZUED WKNNNR WAGEEX
SLKZUD LJKFIX HTKPIA ZMXFAC WCTQID UWBRRL TTKVNA JWVBRE
AWTNSE ZMOECS SVMRSL JMLEEB MMTGAY VIYGHPEMYFAR WAOAEL
UPIUAY YMGEEM JQKSFC GUGYBP JBPZYP JASNNF STUSST YVGYS
Frequency table:
A B C D E F G H I J K L M
2 0 0 0 1 0 2 3 0 6 3 3 3
N O P Q R S T U V W X Y Z
0 0 0 0 0 6 1 5 2 5 0 2 4
Prepared by D Almeida
The second place letters:
ANYVGY STYNRP LWHRDT KXRNYP VQTGHP HZKFEY UMUSAY WVKZYE
ZMEZUD LJKTUL JLKQBJ UQVUEC KBNRCT HPKESX MAZOEN SXGOLP
GNLEEB MMTGCS SVMRSE ZMXHLP KJEJHT UPZUED WKNNNR WAGEEX
SLKZUD LJKFIX HTKPIA ZMXFAC WCTQID UWBRRL TTKVNA JWVBRE
AWTNSE ZMOECS SVMRSL JMLEEB MMTGA YVIYGHP EMYFAR WAOAEL
UPIUAY YMGEEM JQKSFC GUGYBP JBPZYP JASNNF STUSST YVGYS
Now construct frequency table:
ABCDEF......
42100.....
Step 6 Find the frequencies of the 26 letters a, b, c,….., x, y, zin
the other places in each block;
The second place letters:
ANYVGY STYNRP LWHRDT KXRNYP VQTGHP HZKFEY UMUSAY WVKZYE
ZMEZUD LJKTUL JLKQBJ UQVUEC KBNRCT HPKESX MAZOEN SXGOLP
GNLEEB MMTGCS SVMRSE ZMXHLP KJEJHT UPZUED WKNNNR WAGEEX
SLKZUD LJKFIX HTKPIA ZMXFAC WCTQID UWBRRL TTKVNA JWVBRE
AWTNSE ZMOECS SVMRSL JMLEEB MMTGA YVIYGHP EMYFAR WAOAEL
UPIUAY YMGEEM JQKSFC GUGYBP JBPZYP JASNNF STUSST YVGYS
Now construct frequency table:
ABCDEF......
42100.....
Step 6 Find the frequencies of the 26 letters a, b, c,….., x, y, zin
the other places in each block;
Prepared by D Almeida
1st2nd3rd4th5th6th
a 2 4 0 1 4 2
b 0 2 1 1 2 2
c 0 1 0 0 3 3
d 0 0 0 0 1 4
e 1 0 2 6 9 4
f 0 0 0 4 1 1
g 2 0 5 4 1 0
h 3 0 1 1 2 0
i 0 1 1 0 3 0
j 6 3 0 1 0 1
k 3 110 0 0 0
l 3 2 2 0 2 4
m 3 10 2 0 0 1
n 0 2 2 5 3 1
o 0 0 2 2 0 0
p 0 3 1 1 0 8
q 0 3 0 2 0 0
r 0 0 1 5 3 2
s 6 0 1 2 6 2
t 1 4 5 1 0 4
u 5 1 2 3 3 0
v 2 3 2 2 0 0
w 5 4 0 0 0 0
x 0 2 2 0 0 3
y 2 1 4 2 3 5
z 4 1 2 4 0 0
Step 6 Find the frequencies of the 26 letters a, b, c,….., x, y, zin
the 6 places in each block;
This is the completed table of
frequencies of the letters in the
1
st
, 2
nd
, 3
rd
, 4
th
, 5
th
and 6
th
places
1st2nd3rd4th5th6th
a 2 4 0 1 4 2
b 0 2 1 1 2 2
c 0 1 0 0 3 3
d 0 0 0 0 1 4
e 1 0 2 6 9 4
f 0 0 0 4 1 1
g 2 0 5 4 1 0
h 3 0 1 1 2 0
i 0 1 1 0 3 0
j 6 3 0 1 0 1
k 3 110 0 0 0
l 3 2 2 0 2 4
m 3 10 2 0 0 1
n 0 2 2 5 3 1
o 0 0 2 2 0 0
p 0 3 1 1 0 8
q 0 3 0 2 0 0
r 0 0 1 5 3 2
s 6 0 1 2 6 2
t 1 4 5 1 0 4
u 5 1 2 3 3 0
v 2 3 2 2 0 0
w 5 4 0 0 0 0
x 0 2 2 0 0 3
y 2 1 4 2 3 5
z 4 1 2 4 0 0
Step 6 Find the frequencies of the 26 letters a, b, c,….., x, y, zin
the 6 places in each block;
This is the completed table of
frequencies of the letters in the
1
st
, 2
nd
, 3
rd
, 4
th
, 5
th
and 6
th
places
Prepared by D Almeida
1st2nd3rd4th5th6th
Normalrelative
frequency of letters
a240142 8.17%
b021122 1.49%
c010033 2.78%
d000014 4.25%
e102694 12.70%
f000411 2.23%
g205410 2.02%
h301120 6.09%
i011030 6.97%
j630101 0.15%
k3110000 0.77%
l322024 4.03%
m3102001 2.41%
n022531 6.75%
o002200 7.51%
p031108 1.93%
q030200 0.10%
r001532 5.99%
s601262 6.33%
t145104 9.06%
u512330 2.76%
v232200 0.98%
w540000 2.36%
x022003 0.15%
y214235 1.97%
z412400 0.07%
Step 7 Compare the frequencies of the 26 letters a, b, c,….., x, y,
zin the first place with the expected frequencies of the 26
letters: observation will imply a Caesar shift of the letters
Comparison of 1
st
place frequency with that
of expected frequency implies a Caesar shift
of 8.
That is
8
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
8IJKLMNOPQRSTUVWXYZABCDEFGH
1st2nd3rd4th5th6th
Normalrelative
frequency of letters
a240142 8.17%
b021122 1.49%
c010033 2.78%
d000014 4.25%
e102694 12.70%
f000411 2.23%
g205410 2.02%
h301120 6.09%
i011030 6.97%
j630101 0.15%
k3110000 0.77%
l322024 4.03%
m3102001 2.41%
n022531 6.75%
o002200 7.51%
p031108 1.93%
q030200 0.10%
r001532 5.99%
s601262 6.33%
t145104 9.06%
u512330 2.76%
v232200 0.98%
w540000 2.36%
x022003 0.15%
y214235 1.97%
z412400 0.07%
Step 7 Compare the frequencies of the 26 letters a, b, c,….., x, y,
zin the first place with the expected frequencies of the 26
letters: observation will imply a Caesar shift of the letters
Comparison of 1
st
place frequency with that
of expected frequency implies a Caesar shift
of 8.
That is
8
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
8IJKLMNOPQRSTUVWXYZABCDEFGH
Prepared by D Almeida
Step 7 Replace the ciphered letter in each of the first places
with the unciphered one.
INYVGY ATYNRP TWHRDT SXRNYP DQTGHP PZKFEY CMUSAY EVKZYE
HMEZUD TJKTUL RLKQBJ CQVUEC SBNRCT PPKESX UAZOEN AXGOLP
ONLEEB UMTGCS AVMRSE HMXHLP SJEJHT CPZUED EKNNNR EAGEEX
ALKZUD TJKFIX PTKPIA HMXFAC ECTQID CWBRRL BTKVNA RWVBRE
IWTNSE HMOECS AVMRSL RMLEEB UMTGAY DIYGHP MMYFAR EAOAEL
CPIUAY GMGEEM RQKSFC OUGYBP RBPZYP RASNNF ATUSST GVGYS
ANYVGY STYNRP LWHRDT KXRNYP VQTGHP HZKFEY UMUSAY WVKZYE
ZMEZUD LJKTUL JLKQBJ UQVUEC KBNRCT HPKESX MAZOEN SXGOLP
GNLEEB MMTGCS SVMRSE ZMXHLP KJEJHT UPZUED WKNNNR WAGEEX
SLKZUD LJKFIX HTKPIA ZMXFAC WCTQID UWBRRL TTKVNA JWVBRE
AWTNSE ZMOECS SVMRSL JMLEEB MMTGAY VIYGHP EMYFAR WAOAEL
UPIUAY YMGEEM JQKSFC GUGYBP JBPZYP JASNNF STUSST YVGYS
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
8IJKLMNOPQRSTUVWXYZABCDEFGH
This rule for 1
st
place letters
Step 7 Replace the ciphered letter in each of the first places
with the unciphered one.
INYVGY ATYNRP TWHRDT SXRNYP DQTGHP PZKFEY CMUSAY EVKZYE
HMEZUD TJKTUL RLKQBJ CQVUEC SBNRCT PPKESX UAZOEN AXGOLP
ONLEEB UMTGCS AVMRSE HMXHLP SJEJHT CPZUED EKNNNR EAGEEX
ALKZUD TJKFIX PTKPIA HMXFAC ECTQID CWBRRL BTKVNA RWVBRE
IWTNSE HMOECS AVMRSL RMLEEB UMTGAY DIYGHP MMYFAR EAOAEL
CPIUAY GMGEEM RQKSFC OUGYBP RBPZYP RASNNF ATUSST GVGYS
ANYVGY STYNRP LWHRDT KXRNYP VQTGHP HZKFEY UMUSAY WVKZYE
ZMEZUD LJKTUL JLKQBJ UQVUEC KBNRCT HPKESX MAZOEN SXGOLP
GNLEEB MMTGCS SVMRSE ZMXHLP KJEJHT UPZUED WKNNNR WAGEEX
SLKZUD LJKFIX HTKPIA ZMXFAC WCTQID UWBRRL TTKVNA JWVBRE
AWTNSE ZMOECS SVMRSL JMLEEB MMTGAY VIYGHP EMYFAR WAOAEL
UPIUAY YMGEEM JQKSFC GUGYBP JBPZYP JASNNF STUSST YVGYS
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
8IJKLMNOPQRSTUVWXYZABCDEFGH
This rule for 1
st
place letters
Prepared by D Almeida
1st2nd3rd4th5th6th
Normalrelative
frequency of letters
a240142 8.17%
b021122 1.49%
c010033 2.78%
d000014 4.25%
e102694 12.70%
f000411 2.23%
g205410 2.02%
h301120 6.09%
i011030 6.97%
j630101 0.15%
k3110000 0.77%
l322024 4.03%
m3102001 2.41%
n022531 6.75%
o002200 7.51%
p031108 1.93%
q030200 0.10%
r001532 5.99%
s601262 6.33%
t145104 9.06%
u512330 2.76%
v232200 0.98%
w540000 2.36%
x022003 0.15%
y214235 1.97%
z412400 0.07%
Step 7 Compare the frequencies of the 26 letters a, b, c,….., x, y,
zin the second place with the expected frequencies of the 26
letters: observation will imply a Caesar shift of the letters
Comparison of 2
nd
place frequency with that
of expected frequency implies a Caesar shift
of 18:
i.e.
18
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
18STUVWXYZABCDEFGHIJKLMNOPQR
1st2nd3rd4th5th6th
Normalrelative
frequency of letters
a240142 8.17%
b021122 1.49%
c010033 2.78%
d000014 4.25%
e102694 12.70%
f000411 2.23%
g205410 2.02%
h301120 6.09%
i011030 6.97%
j630101 0.15%
k3110000 0.77%
l322024 4.03%
m3102001 2.41%
n022531 6.75%
o002200 7.51%
p031108 1.93%
q030200 0.10%
r001532 5.99%
s601262 6.33%
t145104 9.06%
u512330 2.76%
v232200 0.98%
w540000 2.36%
x022003 0.15%
y214235 1.97%
z412400 0.07%
Step 7 Compare the frequencies of the 26 letters a, b, c,….., x, y,
zin the second place with the expected frequencies of the 26
letters: observation will imply a Caesar shift of the letters
Comparison of 2
nd
place frequency with that
of expected frequency implies a Caesar shift
of 18:
i.e.
18
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
18STUVWXYZABCDEFGHIJKLMNOPQR
Prepared by D Almeida
Step 7 Replace the ciphered letter in each of the second places
with the unciphered one.
INYVGY ATYNRP TWHRDT SXRNYP DQTGHP PZKFEY CMUSAY EVKZYE
HMEZUD TJKTUL RLKQBJ CQVUEC SBNRCT PPKESX UAZOEN AXGOLP
ONLEEB UMTGCS AVMRSE HMXHLP SJEJHT CPZUED EKNNNR EAGEEX
ALKZUD TJKFIX PTKPIA HMXFAC ECTQID CWBRRL BTKVNA RWVBRE
IWTNSE HMOECS AVMRSL RMLEEB UMTGAY DIYGHP MMYFAR EAOAEL
CPIUAY GMGEEM RQKSFC OUGYBP RBPZYP RASNNF ATUSST GVGYS
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
18STUVWXYZABCDEFGHIJKLMNOPQR
IFYVGY ALYNRP TOHRDT SPRNYP DITGHP PRKFEY CEUSAY ENKZYE
HEEZUD TBKTUL RDKQBJ CIVUEC STNRCT PHKESX USZOEN APGOLP
OFLEEB UETGCS ANMRSE HEXHLP SBEJHT CHZUED ECNNNR ESGEEX
ADKZUD TBKFIX PLKPIA HEXFAC EUTQID COBRRL BLKVNA ROVBRE
IOTNSE HEOECS ANMRSL RELEEB UETGAY DAYGHP MEYFAR ESOAEL
CHIUAY GEGEEM RIKSFC OMGYBP RTPZYP RSSNNF ALUSST GNGYS
This rule for 2
nd
place letters
Step 7 Replace the ciphered letter in each of the second places
with the unciphered one.
INYVGY ATYNRP TWHRDT SXRNYP DQTGHP PZKFEY CMUSAY EVKZYE
HMEZUD TJKTUL RLKQBJ CQVUEC SBNRCT PPKESX UAZOEN AXGOLP
ONLEEB UMTGCS AVMRSE HMXHLP SJEJHT CPZUED EKNNNR EAGEEX
ALKZUD TJKFIX PTKPIA HMXFAC ECTQID CWBRRL BTKVNA RWVBRE
IWTNSE HMOECS AVMRSL RMLEEB UMTGAY DIYGHP MMYFAR EAOAEL
CPIUAY GMGEEM RQKSFC OUGYBP RBPZYP RASNNF ATUSST GVGYS
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
18STUVWXYZABCDEFGHIJKLMNOPQR
IFYVGY ALYNRP TOHRDT SPRNYP DITGHP PRKFEY CEUSAY ENKZYE
HEEZUD TBKTUL RDKQBJ CIVUEC STNRCT PHKESX USZOEN APGOLP
OFLEEB UETGCS ANMRSE HEXHLP SBEJHT CHZUED ECNNNR ESGEEX
ADKZUD TBKFIX PLKPIA HEXFAC EUTQID COBRRL BLKVNA ROVBRE
IOTNSE HEOECS ANMRSL RELEEB UETGAY DAYGHP MEYFAR ESOAEL
CHIUAY GEGEEM RIKSFC OMGYBP RTPZYP RSSNNF ALUSST GNGYS
This rule for 2
nd
place letters
Prepared by D Almeida
Step 7 Use common senseand/or comparative frequencies for
the other place letters.
IFYVGY ALYNRP TOHRDT SPRNYP DITGHP PRKFEY CEUSAY ENKZYE
HEEZUD TBKTUL RDKQBJ CIVUEC STNRCT PHKESX USZOEN APGOLP
OFLEEB UETGCS ANMRSE HEXHLP SBEJHT CHZUED ECNNNR ESGEEX
ADKZUD LBKFIX PLKPIA HEXFAC EUTQID COBRRL BLKVNA ROVBRE
IOTNSE HEOECS ANMRSL RELEEB UETGAY DAYGHP MEYFAR ESOAEL
CHIUAY GEGEEM RIKSFC OMGYBP RTPZYP RSSNNF ALUSST GNGYS
This E before HEsuggests E is a T: a Caesar shift of 15 in the 6
th
place
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
15PQRSTUVWXYZABCDEFGHIJKLMNO
IFYVGNALYNRETOHRDISPRNYEDITGHEPRKFENCEUSANENKZYT
HEEZUSTBKTUARDKQBYCIVUERSTNRCIPHKESMUSZOECAPGOLE
OFLEEQUETGCHANMRSTHEXHLESBEJHICHZUESECNNNGESGEEM
ADKZUSTBKFIMPLKPIPHEXFAREUTQISCOBRRABLKVNPROVBRT
IOTNSTHEOECHANMRSARELEEQ UETGANDAYGHEMEYFAGESOAEA
CHIUANGEGEEBRIKSFROMGYBERTPZYERSSNNUALUSSIGNGYS
Step 7 Use common senseand/or comparative frequencies for
the other place letters.
IFYVGY ALYNRP TOHRDT SPRNYP DITGHP PRKFEY CEUSAY ENKZYE
HEEZUD TBKTUL RDKQBJ CIVUEC STNRCT PHKESX USZOEN APGOLP
OFLEEB UETGCS ANMRSE HEXHLP SBEJHT CHZUED ECNNNR ESGEEX
ADKZUD LBKFIX PLKPIA HEXFAC EUTQID COBRRL BLKVNA ROVBRE
IOTNSE HEOECS ANMRSL RELEEB UETGAY DAYGHP MEYFAR ESOAEL
CHIUAY GEGEEM RIKSFC OMGYBP RTPZYP RSSNNF ALUSST GNGYS
This E before HEsuggests E is a T: a Caesar shift of 15 in the 6
th
place
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
15PQRSTUVWXYZABCDEFGHIJKLMNO
IFYVGNALYNRETOHRDISPRNYEDITGHEPRKFENCEUSANENKZYT
HEEZUSTBKTUARDKQBYCIVUERSTNRCIPHKESMUSZOECAPGOLE
OFLEEQUETGCHANMRSTHEXHLESBEJHICHZUESECNNNGESGEEM
ADKZUSTBKFIMPLKPIPHEXFAREUTQISCOBRRABLKVNPROVBRT
IOTNSTHEOECHANMRSARELEEQ UETGANDAYGHEMEYFAGESOAEA
CHIUANGEGEEBRIKSFROMGYBERTPZYERSSNNUALUSSIGNGYS
Prepared by D Almeida
Step 7 Use common senseand/or comparative frequencies for
the other place letters.
IFYVGNALYNRETOHRDISPRNYEDITGHEPRKFENCEUSANENKZYT
HEEZUSTBKTUARDKQBYCIVUERSTNRCIPHKESMUSZOECAPGOLE
OFLEEQUETGCHANMRSTHEXHLESBEJHICHZUESECNNNGESGEEM
ADKZUSTBKFIMPLKPIPHEXFAREUTQISCOBRRABLKVNPROVBRT
IOTNSTHEOECHANMRSARELEEQ UETGANDAYGHEMEYFAGESOAEA
CHIUANGEGEEBRIKSFROMGYBERTPZYERSSNNUALUSSIGNGYS
5th
Normal
frequency
a4 8.17%
b2 1.49%
c3 2.78%
d1 4.25%
e912.70%
f1 2.23%
g1 2.02%
h2 6.09%
i3 6.97%
j0 0.15%
k0 0.77%
l2 4.03%
m0 2.41%
n3 6.75%
o0 7.51%
p0 1.93%
q0 0.10%
r3 5.99%
s6 6.33%
t0 9.06%
u3 2.76%
v0 0.98%
w0 2.36%
x0 0.15%
y3 1.97%
z0 0.07%
This block of letters and the comparative frequency of 5
th
place
letters suggest………..
IFYVGNALYNRETOHRDISPRNYEDITGHEPRKFENCEUSANENKZYT
HEEZUSTBKTUARDKQBYCIVUERSTNRCIPHKESMUSZOECAPGOLE
OFLEEQUETGCHANMRSTHEXHLESBEJHICHZUESECNNNGESGEEM
ADKZUSTBKFIMPLKPIPHEXFAREUTQISCOBRRABLKVNPROVBRT
IOTNSTHEOECHANMRSARELEEQ UETGANDAYGHEMEYFAGESOAEA
CHIUANGEGEEBRIKSFROMGYBERTPZYERSSNNUALUSSIGNGYS
There is no shift for 5
th
place letters
Step 7 Use common senseand/or comparative frequencies for
the other place letters.
IFYVGNALYNRETOHRDISPRNYEDITGHEPRKFENCEUSANENKZYT
HEEZUSTBKTUARDKQBYCIVUERSTNRCIPHKESMUSZOECAPGOLE
OFLEEQUETGCHANMRSTHEXHLESBEJHICHZUESECNNNGESGEEM
ADKZUSTBKFIMPLKPIPHEXFAREUTQISCOBRRABLKVNPROVBRT
IOTNSTHEOECHANMRSARELEEQ UETGANDAYGHEMEYFAGESOAEA
CHIUANGEGEEBRIKSFROMGYBERTPZYERSSNNUALUSSIGNGYS
5th
Normal
frequency
a4 8.17%
b2 1.49%
c3 2.78%
d1 4.25%
e912.70%
f1 2.23%
g1 2.02%
h2 6.09%
i3 6.97%
j0 0.15%
k0 0.77%
l2 4.03%
m0 2.41%
n3 6.75%
o0 7.51%
p0 1.93%
q0 0.10%
r3 5.99%
s6 6.33%
t0 9.06%
u3 2.76%
v0 0.98%
w0 2.36%
x0 0.15%
y3 1.97%
z0 0.07%
This block of letters and the comparative frequency of 5
th
place
letters suggest………..
IFYVGNALYNRETOHRDISPRNYEDITGHEPRKFENCEUSANENKZYT
HEEZUSTBKTUARDKQBYCIVUERSTNRCIPHKESMUSZOECAPGOLE
OFLEEQUETGCHANMRSTHEXHLESBEJHICHZUESECNNNGESGEEM
ADKZUSTBKFIMPLKPIPHEXFAREUTQISCOBRRABLKVNPROVBRT
IOTNSTHEOECHANMRSARELEEQ UETGANDAYGHEMEYFAGESOAEA
CHIUANGEGEEBRIKSFROMGYBERTPZYERSSNNUALUSSIGNGYS
There is no shift for 5
th
place letters
Prepared by D Almeida
Step 7 Use common senseand/or comparative frequencies for
the other place letters.
IFYVGNALYNRETOHRDISPRNYEDITGHEPRKFENCEUSANENKZYT
HEEZUSTBKTUARDKQBYCIVUERSTNRCIPHKESMUSZOECAPGOLE
OFLEEQUETGCHANMRSTHEXHLESBEJHICHZUESECNNNGESGEEM
ADKZUSTBKFIMPLKPIPHEXFAREUTQISCOBRRABLKVNPROVBRT
IOTNSTHEOECHANMRSARELEEQ UETGANDAYGHEMEYFAGESOAEA
CHIUANGEGEEBRIKSFROMGYBERTPZYERSSNNUALUSSIGNGYS
This G and the HEsuggests that G should be a T: a Caesar shift of 13
for the 4
th
place letters
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
13NOPQRSTUVWXYZABCDEFGHIJKLM
IFYIGNALYARETOHEDISPRAYEDITTHEPRKSENCEUFANENKMYT
HEEMUSTBKGUARDKDBYCIVHERSTNECIPHKRSMUSZBECAPGBLE
OFLREQUETTCHANMESTHEXULESBEWHICHZHESECNANGESGREM
ADKMUSTBKSIMPLKCIPHEXSAREUTDISCOBERABLKINPROVORT
IOTASTHEORCHANMESARELREQ UETTANDAYTHEMEYSAGESONEA
CHIHANGEGREBRIKFFROMGLBERTPMYERSSANUALUFSIGNGLS
Step 7 Use common senseand/or comparative frequencies for
the other place letters.
IFYVGNALYNRETOHRDISPRNYEDITGHEPRKFENCEUSANENKZYT
HEEZUSTBKTUARDKQBYCIVUERSTNRCIPHKESMUSZOECAPGOLE
OFLEEQUETGCHANMRSTHEXHLESBEJHICHZUESECNNNGESGEEM
ADKZUSTBKFIMPLKPIPHEXFAREUTQISCOBRRABLKVNPROVBRT
IOTNSTHEOECHANMRSARELEEQ UETGANDAYGHEMEYFAGESOAEA
CHIUANGEGEEBRIKSFROMGYBERTPZYERSSNNUALUSSIGNGYS
This G and the HEsuggests that G should be a T: a Caesar shift of 13
for the 4
th
place letters
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
13NOPQRSTUVWXYZABCDEFGHIJKLM
IFYIGNALYARETOHEDISPRAYEDITTHEPRKSENCEUFANENKMYT
HEEMUSTBKGUARDKDBYCIVHERSTNECIPHKRSMUSZBECAPGBLE
OFLREQUETTCHANMESTHEXULESBEWHICHZHESECNANGESGREM
ADKMUSTBKSIMPLKCIPHEXSAREUTDISCOBERABLKINPROVORT
IOTASTHEORCHANMESARELREQ UETTANDAYTHEMEYSAGESONEA
CHIHANGEGREBRIKFFROMGLBERTPMYERSSANUALUFSIGNGLS
Prepared by D Almeida
Step 7 Use common senseand/or comparative frequencies for
the other place letters.
IFYIGNALYARETOHEDISPRAYEDITTHEPRKSENCEUFANENKMYT
HEEMUSTBKGUARDKDBYCIVHERSTNECIPHKRSMUSZBECAPGBLE
OFLREQUETTCHANMESTHEXULESBEWHICHZHESECNANGESGREM
ADKMUSTBKSIMPLKCIPHEXSAREUTDISCOBERABLKINPROVORT
IOTASTHEORCHANMESARELREQ UETTANDAYTHEMEYSAGESONEA
CHIHANGEGREBRIKFFROMGLBERTPLYERSSANUALUFSIGNGLS
3rd
Normalfreq
a0 8.17%
b1 1.49%
c0 2.78%
d0 4.25%
e2 12.70%
f0 2.23%
g5 2.02%
h1 6.09%
i1 6.97%
j0 0.15%
k10 0.77%
l2 4.03%
m2 2.41%
n2 6.75%
o2 7.51%
p1 1.93%
q0 0.10%
r1 5.99%
s1 6.33%
t5 9.06%
u2 2.76%
v2 0.98%
w0 2.36%
x2 0.15%
y4 1.97%
z2 0.07%
Comparative high frequency of K’s in 5
th
place suggest K must be an
E: a Caesar shift 0f 20.
IFSIGNALSARETOBEDISPLAYEDINTHEPRESENCEOFANENEMYT
HEYMUSTBEGUARDEDBYCIPHERSTHECIPHERSMUSTBECAPABLE
OFFREQUENTCHANGESTHERULESBYWHICHTHESECHANGESAREM
ADEMUSTBESIMPLECIPHERSAREUNDISCOVERABLEINPROPORT
IONASTHEIRCHANGESAREFREQ UENTAN DASTHEMESSAGESINEA
CHCHANGEAREBRIEFFROMALBERTJMYERSMANU ALOFSIGNALS
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
20UVWXYZABCDEFGHIJKLMNOPQRST
Step 7 Use common senseand/or comparative frequencies for
the other place letters.
IFYIGNALYARETOHEDISPRAYEDITTHEPRKSENCEUFANENKMYT
HEEMUSTBKGUARDKDBYCIVHERSTNECIPHKRSMUSZBECAPGBLE
OFLREQUETTCHANMESTHEXULESBEWHICHZHESECNANGESGREM
ADKMUSTBKSIMPLKCIPHEXSAREUTDISCOBERABLKINPROVORT
IOTASTHEORCHANMESARELREQ UETTANDAYTHEMEYSAGESONEA
CHIHANGEGREBRIKFFROMGLBERTPLYERSSANUALUFSIGNGLS
3rd
Normalfreq
a0 8.17%
b1 1.49%
c0 2.78%
d0 4.25%
e2 12.70%
f0 2.23%
g5 2.02%
h1 6.09%
i1 6.97%
j0 0.15%
k10 0.77%
l2 4.03%
m2 2.41%
n2 6.75%
o2 7.51%
p1 1.93%
q0 0.10%
r1 5.99%
s1 6.33%
t5 9.06%
u2 2.76%
v2 0.98%
w0 2.36%
x2 0.15%
y4 1.97%
z2 0.07%
Comparative high frequency of K’s in 5
th
place suggest K must be an
E: a Caesar shift 0f 20.
IFSIGNALSARETOBEDISPLAYEDINTHEPRESENCEOFANENEMYT
HEYMUSTBEGUARDEDBYCIPHERSTHECIPHERSMUSTBECAPABLE
OFFREQUENTCHANGESTHERULESBYWHICHTHESECHANGESAREM
ADEMUSTBESIMPLECIPHERSAREUNDISCOVERABLEINPROPORT
IONASTHEIRCHANGESAREFREQ UENTAN DASTHEMESSAGESINEA
CHCHANGEAREBRIEFFROMALBERTJMYERSMANU ALOFSIGNALS
0ABCDEFGHIJKLMNOPQRSTUVWXYZ
20UVWXYZABCDEFGHIJKLMNOPQRST
Prepared by D Almeida
Step 8 Partition to reveal message.
IF|SIGNALS|ARE|TO|BE|DISPLAYED|IN|THE|PRESENCE|OF|AN|ENEMY|
THEY|MUST|BE|GUARDED|BY|CIPHERS|THE|CIPHERS|MUST|BE|
CAPABLE|OF|FREQUENT|CHANGES|THE|RULES|BY|WHICH|THESE|
CHANGES|ARE|MADE|MUST|BE|SIMPLE|CIPHERS|ARE|UNDISCOVERABLE|
IN|PROPORTION|AS|THEIR|CHANGES|ARE|FREQUENT|AND|AS|THE|
MESSAGES|IN|EACH|CHANGE|ARE|BRIEF|FROM|ALBERTJMYERS|MANUAL|
OF|SIGNALS|
IFSIGNALSARETOBEDISPLAYEDINTHEPRESENCEOFANENEMYT
HEYMUSTBEGUARDEDBYCIPHERSTHECIPHERSMUSTBECAPABLE
OFFREQUENTCHANGESTHERULESBYWHICHTHESECHANGESAREM
ADEMUSTBESIMPLECIPHERSAREUNDISCOVERABLEINPROPORT
IONASTHEIRCHANGESAREFREQ UENTAN DASTHEMESSAGESINEA
CHCHANGEAREBRIEFFROMALBERTJMYERSMANU ALOFSIGNALS
Step 8 Partition to reveal message.
IF|SIGNALS|ARE|TO|BE|DISPLAYED|IN|THE|PRESENCE|OF|AN|ENEMY|
THEY|MUST|BE|GUARDED|BY|CIPHERS|THE|CIPHERS|MUST|BE|
CAPABLE|OF|FREQUENT|CHANGES|THE|RULES|BY|WHICH|THESE|
CHANGES|ARE|MADE|MUST|BE|SIMPLE|CIPHERS|ARE|UNDISCOVERABLE|
IN|PROPORTION|AS|THEIR|CHANGES|ARE|FREQUENT|AND|AS|THE|
MESSAGES|IN|EACH|CHANGE|ARE|BRIEF|FROM|ALBERTJMYERS|MANUAL|
OF|SIGNALS|
IFSIGNALSARETOBEDISPLAYEDINTHEPRESENCEOFANENEMYT
HEYMUSTBEGUARDEDBYCIPHERSTHECIPHERSMUSTBECAPABLE
OFFREQUENTCHANGESTHERULESBYWHICHTHESECHANGESAREM
ADEMUSTBESIMPLECIPHERSAREUNDISCOVERABLEINPROPORT
IONASTHEIRCHANGESAREFREQ UENTAN DASTHEMESSAGESINEA
CHCHANGEAREBRIEFFROMALBERTJMYERSMANU ALOFSIGNALS
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