CRYPTOGRAPHY

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CRYPTOGRAPHY

• lecture 3
• Wednesday

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(No Transcript)
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The difference between substitution and
transposition is that in Subtitution each
letter retains its position but changes its
identity, Transposition each letter retains its
identity but changes its position.
Example 3
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HW 2 Caesar shift problems

• 2. KENKMOC PYBDEXK TEFKD
• 3.MHILYLZAZBHLXBPZXBLMVYABUHLHWWPBZJSHBKPBZJHLJBZK
  PJABTHYJHUBTLZAULBAYVU

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• QK MEJXNEJJ ZMEVTJ Q YVNGEZ VNHKE KVMMHY JXMEEXJ
  HB FHWWNEJXHKE WEKEVXP XPE PVNH HB V JXMEEX NVTI
  Q XRMK TA FHNNVM XH XPE FHNZ VKZ ZVTI YPEK TA
  EAEJ YEME JXVWWEZ WA XPE BNVJP HB V KEHK NQDPX
  XPVX JINQX XPE KQDPX VKZ XHRFPEZ XPE JHRKZ HB
  JQNEKFE

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new ciphers

• MPV DIZ DFF EPUQH D WZIM QUSZ NPY EZSUBJZIUQH
  GZTTDHZT UT UC KVQ
• HGJUBQPU V HY H CVP AHT BA DHQG ZVYBT V KB GVZJRT
  JB BJURW YQZVE JBB CQJ ZVTER VJ VZ YBZJGS
  EGHZZVEHG VJ KBRZ TBJ VTZDVWR HTS EVDURWR

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new ciphers

• HGJUBQPU V HY H CVP AHT BA DHQG ZVYBT V KB GVZJRT
  JB BJURW YQZVE JBB CQJ ZVTER VJ VZ YBZJGS
  EGHZZVEHG VJ KBRZ TBJ VTZDVWR HTS EVDURWR

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Mono-alphabetic Substitution Cipher

• Allow any permutation of the alphabet
• Each letter is replaced by a different letter or
  symbol
• Key permutation (still need to decide on a key
  and exchange this information in a secure way).
• 26! Possibilities
• What does this mean?

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Frequency Analysis
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HW 3 Reading

• Review The Code Book chapter 1 read chapter 2
  p. 45-51
• Find websites on substitution ciphers and
  frequency analysis
• Begin research for a 5-7 page essay on Why are
  substitution and transposition ciphers obsolete,
  and when did they become so. Due on Monday in
  class.

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(in class) Substitution cipher
SK BKGKC FBTKCHZWBT W ZXUBA HM SKOO, WBT EWQK
UZ MFC MSB, WH SXKB SK XWGK TUHJMGKCKT UZ DMC
MFCHKOGKH
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(in class) Substitution cipher
CGXTOUNZL NQ UDOU HDNTD BCJONLQ HDCL ZLC DOQ
WZBMZUUCL CACBEUDNLM DC KCOBLCG NL QTDZZK.
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HW 3 Substitution cipher
UWZEZ VTPUW ZBEIK WVRWT UPUZT UWPUV YZFZE PAIQB
SISVT RBFZE TZJPR UNIKW PUUWZ GAVFZ ETZVT YBEPA
SKWIV UVTWZ EZVUK VNNVA TUPAU NISVT PCCZP
EPASQ ZEZCN PRZSQ ITBOZ UWVAX ZFZAO BEZQV HPEEZ
PASVA ZJCNV RPQNZ UWZEZ VTPAB UWZEU WZBEI KWVRW
TUPUZ TUWPU UWVTW PTPNE ZPSIW PCCZA ZS
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HW 3 Substitution cipher
VBIPA PMBIE DQFJI DTBQR WPIUI PMJAM HIEDR IJPIE
IJJWF YTDFD PIGID GLIMD NAJJD LUIMB IGDLA MAEWL
HWPNJ VBAEB BWUIE DPPIE MINMB IRVAM BWPDM BIFWP
NMDWJ JQRIW RDPKM BIGDV IFJDT MBIIW FMBMB IJIGW
FWMIW PNISQ WLJMW MADPM DVBAE BMBIL WVJDT PWMQF
IWPND TPWMQ FIJKD NIPMA MLIMB IRWNI EIPMF IJGIE
MMDMB IDGAP ADPJD TRWPO APNFI SQAFI JMBWM MBIYJ
BDQLN NIELW FIMBI EWQJI JVBAE BARGI LMBIR MDMBI
JIGWF WMADP
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HW 3 Substitution cipher
NBSQF VKLUV GZSGN BGVZQ SZMCR GZUVG RHABI FHSVW
XGZMT VLMVE LQSGV LSGVQ TRUVM RGLKC GRHCV ZQZMC
NRMVG VXZMM LSNRH HSGVQ VMVUV QDZHZ AZQTZ RMAVS
SVQCQ RUVMG RHGVZ QSRMN VPVVO HNVZM CGRNR MLMVN
BGVZQ SRMGR NGRHS GLFTG SHZMC HVMHV HTFRC VHGVK
LUVHN BGVZQ SELQL MXVRS DZHGR HLDMR XGVQR HGGRH
AVXZF HVRMN VRSAR CVHGR HGVZQ SGRHD LFMCQ VXVRU
VCEQL NNBHR TGSNB GVZQS DZHDL FMCVC DRSGG RHDLF
MCVCG VZQSE LQZHE QLNNV LMGRN GRHGF QSCRC KRTGS
HLHSR KKNVS GLFTG SRMNV GRHGF QSCRC HNZQS ALSGV
JFZKG FQSRM SGRHX GZMTV HLFTG SLFQA KRHHN BSQFV
KLUVG ZSGNB GVZQS ZMCRG ZUVGR H
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HW 3 Substitution cipher
826821526251162515231172625148114  
14826232621111161411615142623722526  
14826168262326172213262514826232621111  
11221614231252212142221622161827182625  
8262326116252026232671782152625148114  
14826232621111161411615142623722526  
252610711112512011  
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Websites which help
http//www.geocities.com/cryptogramcorner/ http/
/cs.colgate.edu/faculty/nevison/Core139Web/tools/s
ubstitution.html
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What can we do to improve the substitution cipher?
In 1460 Battista Alberti wrote an essay on what
he believed to be a new form of cipher use two
or more cipher alphabets alternately to encrypt a
message.
ABCDEFGHIJKLMNOPQRSTUVWXYZ plain
text GHIJKLMNOPQRSTUVWXYZABCDEF cipher1 RSTUVWXYZA
BCDEFGHIJKLMNOPQ cipher2
Lets encrypt the statement IT IS WAY TOO EARLY
IN THE DAY TO BE DOING THIS OK OJ CRE KUF KRXCE
ZT KNV JRE KU SK UUZTX ZYOJ 12 34 567 890 12345
67 890 123 45 67 89012 3456
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What can we do to improve the substitution cipher?
Alberti was followed by Johannes Trithemius (born
1462) and Giovanni Porta (born 1535) who
developed his ideas. Finally, Vigenere put all
these ideas together. Lets take a whole table
of Caesar shift alphabets. The first row will
have a Caesar shift of 1, the second of 2, etc.
Each letter in the plaintext message can be
enciphered by a different row.
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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 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 A C D E F G H I J K L M N O P Q R S T U V W
X Y Z A B D E F G H I J K L M N O P Q R S T U V W
X Y Z A B C E F G H I J K L M N O P Q R S T U V W
X Y Z A B C D F G H I J K L M N O P Q R S T U V W
X Y Z A B C D E G H I J K L M N O P Q R S T U V W
X Y Z A B C D E F H I J K L M N O P Q R S T U V W
X Y Z A B C D E F G I J K L M N O P Q R S T U V W
X Y Z A B C D E F G H J K L M N O P Q R S T U V W
X Y Z A B C D E F G H I K L M N O P Q R S T U V W
X Y Z A B C D E F G H I J L M N O P Q R S T U V W
X Y Z A B C D E F G H I J K M N O P Q R S T U V
W X Y Z A B C D E F G H I J K L N O P Q R S T U
V W X Y Z A B C D E F G H I J K L M O P Q R S T
U V W X Y Z A B C D E F G H I J K L M N P Q R S
T U V W X Y Z A B C D E F G H I J K L M N O Q R
S T U V W X Y Z A B C D E F G H I J K L M N O P
R S T U V W X Y Z A B C D E F G H I J K L M N O
P Q S T U V W X Y Z A B C D E F G H I J K L M N
O P Q R T U V W X Y Z A B C D E F G H I J K L M
N O P Q R S U V W X Y Z A B C D E F G H I J K L
M N O P Q R S T V W X Y Z A B C D E F G H I J K
L M N O P Q R S T U W X Y Z A B C D E F G H I J
K L M N O P Q R S T U V X Y Z A B C D E F G H I
J K L M N O P Q R S T U V W Y Z A B C D E F G H
I J K L M N O P Q R S T U V W X Z 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
Vigenere cipher Start with a table of Caesar
shift alphabets.
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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 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 A C D E F G H I J K L M N O P Q R S T U V W
X Y Z A B D E F G H I J K L M N O P Q R S T U V W
X Y Z A B C E F G H I J K L M N O P Q R S T U V W
X Y Z A B C D F G H I J K L M N O P Q R S T U V W
X Y Z A B C D E G H I J K L M N O P Q R S T U V W
X Y Z A B C D E F H I J K L M N O P Q R S T U V W
X Y Z A B C D E F G I J K L M N O P Q R S T U V W
X Y Z A B C D E F G H J K L M N O P Q R S T U V W
X Y Z A B C D E F G H I K L M N O P Q R S T U V W
X Y Z A B C D E F G H I J L M N O P Q R S T U V W
X Y Z A B C D E F G H I J K M N O P Q R S T U V
W X Y Z A B C D E F G H I J K L N O P Q R S T U
V W X Y Z A B C D E F G H I J K L M O P Q R S T
U V W X Y Z A B C D E F G H I J K L M N P Q R S
T U V W X Y Z A B C D E F G H I J K L M N O Q R
S T U V W X Y Z A B C D E F G H I J K L M N O P
R S T U V W X Y Z A B C D E F G H I J K L M N O
P Q S T U V W X Y Z A B C D E F G H I J K L M N
O P Q R T U V W X Y Z A B C D E F G H I J K L M
N O P Q R S U V W X Y Z A B C D E F G H I J K L
M N O P Q R S T V W X Y Z A B C D E F G H I J K
L M N O P Q R S T U W X Y Z A B C D E F G H I J
K L M N O P Q R S T U V X Y Z A B C D E F G H I
J K L M N O P Q R S T U V W Y Z A B C D E F G H
I J K L M N O P Q R S T U V W X Z 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
SAVEMEPLEASE plain text CRYPTOGRAMCR
keyword URTTFSVCEMUV enciphered The first
letter, S is encrypted using the row beginning
with C The second letter, A is encryted using the
row beginning with R The third letter, V is
encrypted using the row beginning with Y The
fourth letter, E, is encrypted using the row
beginning with P. And so on . . .
You can use http//www.simonsingh.net/The_Black_Ch
amber/v_square.html
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Vigenere cipher

• Frequency analysis does not apply.
• Enormous number of possible keys
• The Vigenere cipher is a polyalphabetic cipher.
• It was then neglected for 2 centuries it is
  hard to break but also hard to encrypt.

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Vigenere cipher the unbreakable code

• At first glance the Vigenère Cipher appears to be
  unbreakable, due to its use of up to 26 different
  cipher alphabets. Ciphers like this, which use
  more than one cipher alphabet are known as
  Polyalphabetic Ciphers. These can be incredibly
  difficult to decipher, because of their
  resistance to letter frequency analysis. Indeed,
  over time, the Vigenère cipher became known as
  'Le Chiffre Undechiffrable', or 'The Unbreakable
  Cipher'.

This slide and the next few copied directly from
Simon Singhs website.
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Ciphers

• Monoalphabetic ciphers each letter in the
  plaintext is encoded by only one letter from the
  cipher alphabet, and each letter in the cipher
  alphabet represents only one letter in the
  plaintext.
• Polyalphabetic ciphers each letter in the
  plaintext can be encoded by any letter in the
  cipher alphabet, and each letter in the cipher
  alphabet may represent different letters from the
  plaintext each time it appears.