Properties of Cipher Texts

Properties of Cipher Texts

Expert System for Analyzing Simple Ciphers: Properties of Cipher Texts Carolyn Rucci Advisor: Ralph Morelli 1 year project Overview What are letter frequencies and index of coincidence. What index of coincidence and patterns of letter frequencies does each cipher follow? Transposition Caesar

Affine Vigenre Playfair Summary What next? Review of Letter Frequencies and Index of Coincidence Letter Frequencies abcdefghijklmnopqrstuvwxyz monographic frequency distribution of normal alphabet Index of Coincidence thisisatestoftheindexofcoincidenceinmessages thisisatestoftheindexofcoincidenceinmessagest hi 5matches / 44letters ~ 11% Transposition Cipher Simply rearranges the letters same letters present in cipher text as plain text

Reverse text: there once was a cat named fred derf deman tac a saw ecno ereht Conclusion: Frequency distribution will be the same. Caesar Each cipher letter corresponds to the plain text letter three after it. Plain Alphabet: 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 Caesar Alphabet: 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 the quick fox jumped over the lazy dog Shift 3

wkh txlfn ira mxpshg ryhu wkh odcb grj Conclusion: Frequency distribution will match when shifted three Affine Each cipher letter corresponds to exactly one plain text letter. C = (aP + b) mod 26 Ex: a=4 and b=5: A = (4*1 + 5) mod 26 = 9 I Conclusion: Plain remainder Cipher

B 13 M C 17 Q D 21 U E 25 Y F 3 C

Same frequencies will be present but in a random Vigenre Many cipher alphabets created based on keyword. Conclusion: No pattern to letter frequencies. Find identical sequences of letters. the frog jumping the fence dlc bffj tyklwej dlc bsefo Calculate interval bt/w sequences If interval between two C I

P H E R ABCDEFXY Z ABCDEFXY Z BCDEFGYZ A C D E F GH Z A B A :B C D E F X Y Z ... H VIJ K KY LZ MANBOCPD XH I J K B C D E EW FG Y YZ ZA AB BC CD D EVW

WX W WXXYY Z A B U V W OOPQRST LMN R RSTUVW OPQ D DEFGH I ABC Playfair Mixed alphabetic sequence of 25 letters is written into a 5x5 square (J normally omitted). D C Q Z L B O Y A U M X R K H

W G F T M Conclusion: I E S P V Case1: 2corners replace w/other corners Case2: same row replace w/letters to right Case3: same column replace w/letters below No pattern of letter Summary of Findings Index of Frequency Distribution Coinciden (compared to normal) ce

~6.6% Same Transpositi on ~6.6% Will match if shifted 3 to Caesar right ~6.6% Same frequencies Affine present but in different orders Vigenre ~3.8% Flat distribution Review of Letter Frequencies and Index of Coincidence Letter Frequencies abcdefghijklmnopqrstuvwxyz monographic frequency distribution of normal alphabet

Index of Coincidence thisisatestoftheindexofcoincidenceinmessages thisisatestoftheindexofcoincidenceinmessagest hi 5matches / 44letters ~ 11% What Next? Finalize criteria for distinguishing between Vigenre and Playfair ciphers. Create a Java program that: 1) 2) Examines index of coincidence and patterns of frequencies Uses this information to determine which cipher was used

Recently Viewed Presentations

  • Dyslexia and EAL

    Dyslexia and EAL

    Title: Dyslexia and EAL Author: Neil MacKay Last modified by: CCC Kei Wai Pri Sch (Ma Wan) Created Date: 11/24/2003 11:51:50 AM Document presentation format
  • Chemistry - Henry County School District

    Chemistry - Henry County School District

    All swans are white. Prediction: The next swan I see will be white. Thinking Like A Scientist 1.3Understand important features of the process of scientific inquiry. Note, however, that although the prediction is useful, ...
  • Interview Question Types - Centers for Disease Control and ...

    Interview Question Types - Centers for Disease Control and ...

    Interview Question Types. Closed-ended questions. Open-ended questions. Probing questions. Checking questions. State that a variety of question types will be discussed on the following slides. State that the interviewer must know when to use the appropriate type of question to...
  • DBQ Powerpoint II - rhsweb.org

    DBQ Powerpoint II - rhsweb.org

    Relevant thesis develops ALL parts of the question in an original way. Samples… U.S. overseas expansion was seen as imperialistic by some yet other Americans viewed the practice as a necessary evolution of the American identity from an insular self-sufficient...
  • Ed Walton US Networking Sales Leader  2014 Avaya

    Ed Walton US Networking Sales Leader 2014 Avaya

    TipsFor ATF - MaximizingYourROI . Visit the Exhibit Hall. Engage - Q&A . Have fun - Twitter Contest. Tap the experts. Talk with other customers. See it live, then take SPB for a test drive. Let's get going!
  • Bild 1 - jonaskemi.weebly.com

    Bild 1 - jonaskemi.weebly.com

    2. Orsaker Växthuseffekten Växthuseffekten Naturliga och onaturliga klimatvariationer Människans påverkan Människans påverkan Koldioxidutsläppen ökar Sveriges koldioxidutsläpp Olika växthusgaser Växthusgaserna isolerar jorden Utan växthuseffekt - minus 18 grader kallt En ökning av växthusgaser skapar obalans Bild 2.1.1 - Växthuseffekten Bild: Animerad...
  • Galen's Theory of the Four Temperaments (130-200 A.D.)

    Galen's Theory of the Four Temperaments (130-200 A.D.)

    The Law of Pragnanz All cognitive experiences will be as organized, simple, and regular as they can possibly be. Some Gestalt Principles of Organization Figure & Ground (Reversible Figures; Figural Persistence) Grouping Perceptual Constancies Illusions GROUPING Proximity Similarity Symmetry Good...
  • Hinged Alleghanian Uplift of the Bronson Hill terrane in ...

    Hinged Alleghanian Uplift of the Bronson Hill terrane in ...

    Hinged Alleghanian Uplift of the Bronson Hill terrane in Connecticut and Massachusetts Elizabeth R. Goeke, Julie L. Boyd, and Robert P. Wintsch Indiana University, Bloomington, Indiana Research support by: Geological Society of America Student Research grants awarded to Elizabeth R....