Monoalphabetic Ciphers

1
Monoalphabetic Ciphers

• Summary

2
Caesar Cipher

• Shift of alphabet (additive)
• Same order of letters, just shifted
• Analysis can include patterns of frequency

3
Affine Cipher

• Two keys
• Add s to plaintext value
• Multiply result by t
• Reduce mod 26
• Susceptible to frequency analysis
• Single letter
• Digrams
• Brute force

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Keyword scramble, with shift

• Keyword and letter
• Scrambled alphabet starts with keyword (duplicate
  letters eliminated) followed by rest of alphabet,
  with keyword letters left out.
• Can be shifted so keyword begins at letter key
• Susceptible to frequency analysis, with guesses
  at keyword when some letters are found

5
Summary

• Monalphabetic not secure because of frequency
  analysis
• Easy to remember keys (Caesar, single number
  Affine, two numbers keyword, letter)