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The strongest possible substitution ciphers replace each letter with a random substitute. But even these are easily broken by simple analyses of letter and digram frequencies. In fact, newspaper "cryptograms" are nothing more than substitution ciphers, and readers are expected to solve them in an hour or so.
The strongest possible substitution ciphers replace each letter with a random substitute. But even these are easily broken by simple analyses of letter and digram frequencies. In fact, newspaper "cryptograms" are nothing more than substitution ciphers, and readers are expected to solve them in an hour or so.
Each letter can be replaced by an arbitrary symbol rather than a letter, as in this example from the Sherlock Holmes story ''The Adventure of the Dancing Men:''
[[Image:Dancingmen2.png]]
Logically, this does not make the cryptogram any harder to solve, but it may make it ''look'' more puzzling, or even disguise the fact that a secret message has been encrypted.