Which is the strongest/code that is unbreakable and exists? I have recently been reading a book called: The Code Book" by Simon Singh and It doesn't specify what was/is the most unbreakable code ever created by mankind? (the Answer can be a code or a list of codes)

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    How would this be a history question? And what standards are there to determine difficulty? If these standards are mathematical/scientific, then is not the question better suited for another forum? – Rajib Feb 21 '15 at 8:48
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    Are you taking about codes or encryption? – Steve Bird Feb 21 '15 at 12:16
  • @Steve Bird, since the average person does not know the difference between a code and a cipher, and he is referring to Simon Singh's Code Book which is almost entirely about ciphers we may safely assume he means either. – Conrad Turner Feb 21 '15 at 17:27

Common knowledge: The One Time Pad is in theory unbreakable (and in practice if properly managed - I'm looking at you Soviet Union).

This is a Poly-alphabetic substitution cipher with a random key (in effect infinity long).

  • Note that an OTP is utter crap if you weaken its constraints in even minor ways, and does not provide authenticity, being highly vulnerable to manipulation if the attacker knows some of the plaintext. – cpast Feb 22 '15 at 5:45

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