Cryptology Cylinder Ciphers—Consequences from Cryptanalysis

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Advantages and Disadvantages of Cylinder Ciphers

+	Independent alphabets
+	Comfortable and easy to use
+	Error-tolerant
+	Large keyspace
–	Relatively short period
–	Vulnerable to negative pattern search
–	Susceptible to positive pattern search, if the cipher equivalents of the letters are non-uniformly distributed [that is, the alphabet table is not a Latin Square]
–	Alphabets can hardly kept secret.
–	Using different generatrices is an illusory complication.

General Lessons From the Cryptanalysis

• Never trust a cipher until the leading experts analyzed it thoroughly.
• Avoid any statistical irregularities in constructing a cipher.
• Check each additional complexity for an illusory complication.
• A method that is immune against all known attacks may miserably fail under a new attack.

Possible Further Improvements of Polyalphabetic Substitution

• Lengthening of the period,
  say by
  • overlay of different periods
    → key generators
  • combining several periodic substitutions
    → rotor machines
• Aperiodic polyalphabetic substitutions
  → running text ciphers
• More complex transformations inside the plaintext blocks
  → product ciphers