Shannon Cipher

Updated 03 Sep 2026

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Definition
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  a pair $\mathcal{E} = (E, D)$ of functions defined over a key space $K$ , message space $M$ , and ciphertext space $C$
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  $E: K \times M \to C$ (encryption) and $D: K \times C \to M$ (decryption)
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Correctness property
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  for all keys $k$ and messages $m$ : $D(k, E(k, m)) = m$
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Note
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  this is a simplified, idealized notion — it doesn't require the functions to be efficiently computable; that practical refinement is a Computational Cipher
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Related

Linked references 6