Week 2 Handout

History of Cryptography – Week 2 Handout

New Terms

  • monogram: Single letter
  • bigram: Two-letter combination
  • trigram: Three-letter combination

Frequency Analysis

English Letter Frequency Chart

frequencyAnalysis

Erik’s Cyphertext

KIESY ATKNC OEYPM WANTE MIECN VIMDL UADPR AEKKU ANBEK YCRKM YJJWK
TNEKY CRYAA MIYMK OEKMD LRYJT YCROJ NVIMB EEMNC IEJYK FEUMY CRIEJ
EWEKM IPKBE AADSE RMDMI YMMEC REJAN VIMSI NUIIE YQECM DVYPR WRYWR
ECNEK 

Playfair Cipher

Here’s an illustrated example of the Playfair Cipher.

  1. If both letters are the same (or only one letter is left), add an “X” after the first letter. Encrypt the new pair and continue.
  2. If the letters appear on the same row of your table, replace them with the letters to their immediate right respectively (wrapping around to the left side of the row if a letter in the original pair was on the right side of the row).
  3. If the letters appear on the same column of your table, replace them with the letters immediately below respectively (wrapping around to the top side of the column if a letter in the original pair was on the bottom side of the column).
  4. If the letters are not on the same row or column, replace them with the letters on the same row respectively but at the other pair of corners of the rectangle defined by the original pair. The order is important: the first letter of the encrypted pair is the one that lies on the same row as the first letter of the plaintext pair.

Screenshot from 2015-05-11 14:06:45

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