More Ancient Cryptography

• Greek - "Polybius Square”

• \ 1 2 3 4 5

• \_________

• 1|A B C D E

• 2|F G H I J

• 3|K L M N O

• 4|P Q R S T

• 5|U V W X Y/Z

• T=54

• H=32 5344 44 4435

• I=42 4224 24 3211

• S=44

• The Polybius Square (slightly modified)

• The Caesar Cipher

• ABCDEFGHIJKLMNOPQRSTUVWXYZ

• CDEFGHIJKLMNOPQRSTUVWXYZAB

• Decode VJKU

• Cryptanalysis:

  • Arabic author, Qalqashandi
    • Middle ages
    • Write down the frequency of all symbols
    • Use average frequency of letters in the language to rewrite plaintext

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