Cryptography The Art & Science of Secret-Writing.

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Presentation transcript:

Cryptography The Art & Science of Secret-Writing

Monoalphabetic Substitution Ciphers  Caesar Shift  Keyword with Caesar Shift  Shuffling letters

Invention of Cryptanalysis  Arab mathematicians  Adab al-Kuttāb (The Secretaries’ Manual)  Requires sophisticated knowledge of three different disciplines:  Mathematics  Statistics  Linguistics

First Records of Cryptanalysis  9 th Century  Abū Yūsūf Ya’qūb ibn Is-hāq ibn as-Sabbāh ibn ‘omrān ibn Ismaīl al-Kindī  Author of 290 books on medicine, astronomy, mathematics, linguistics and music  Greatest treatise: A Manuscript on Deciphering Cryptographic Messages

Frequency Analysis

Tables of Relative Frequencies

Variations  No text will have these exact frequencies in letter distribution—the tables are based on averages.  Shorter texts will have more variation than longer ones.

Cryptanalyzing a Ciphertext PCQ VMJYPD LBYK LYSO KBXBJXWXV BXV ZCJPO EYPD KBXBJYUXJ LBJOO KCPK. CP LBO LBCMKXPV XPV IYJKL PYDBL, QBOP KBO BXV OPVOV LBO LXRO CI SX’XJMI, KBO JCKO XPV EYKKOV LBO DJCMPV ZOICJO BYS, KXUYPD: “DJOXL EYPD, ICJ X LBCMKXPV XPV CPO PYDBLK Y BXNO ZOOP JOACMPLYPD LC UCM LBO IXZROK CI FXKL XDOK XPV LBO RODOPVK CI XPAYOPL EYPDK. SXU Y SXEO KC ZCRV XK LC AJXNO X IXNCMJ CI UCMJ SXGOKLU?” OFYRCDMO, LXROK IJCS LBO LBCMKXPV XPV CPO PYDBLK

Frequency of Scrabble Letters  What are the frequency of the letter tiles in Scrabble?  Are they the “correct” ones?  Are the points appropriately assigned? Write a memo to Hasbro Co. explaining your recommendations for changes to the Scrabble game—with a rationale as to why these changes make sense. If you feel no changes are needed, write to Hasbro explaining what about their design you approve of (and why).