# Tag Info

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a bit of history Historically, one-time pads written on paper were almost invariably one of two types: "alphabetic" or "decimal". CT-46 is one type of straddling checkerboard encoding -- but CT-46 assumes you are using a decimal one-time pad. Alphabetic ("base 26"): the key pad has groups of 5 alphabetic letters 'A' through 'Z'. Using these pads requires ...

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Your calculator is correct: $$105-48 = 57 \equiv 5 \pmod{26}.$$ Your Python code, however, calculates 105 - 48 % 26, which Python, due to its operator precedence rules, evaluates as 105 - (48 % 26) = 105 - 22 = 83. To get the correct remainder modulo 26, you need to add parentheses to your Python code so that it reads (105 - 48) % 26 instead. This will ...

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In modular calculations such as this, the divisor (in your case 26) must be at least the size of your character code space. Your code space is 46 characters, so that is not going to work. Any output of the modular calculation will be less than the divisor, so you will never get 83 for x mod 26, it is not going to happen. For a 46 character code space, 46 is ...

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Actually, the problem with OTP isn't the storage of the pad (although secure erasure of the parts of the pad you used is trickier than it looks), and it isn't the pad generation (although, again, that's trickier than it looks), but the secure transport. After all, it's not enough for you (Alice) to have the secure pad, you also have to give a copy to the ...

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It is safe, in the case that you have MACs which are independently keyed (or at the very least, the cryptographically secure MAC is independently keyed from all the other ones). This can be seen not by an argument from randomness, but from a simple observation that it were not true, then an attacker could attack the secure MAC by generating the insecure ...

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Perfect Secrecy (or information-theoretic secure) means that the ciphertext conveys no information about the content of the plaintext. In effect this means that, no matter how much ciphertext you have, it does not convey anything about what the plaintext and key were. It can be proved that any such scheme must use at least as much key material as there is ...

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Perfect secrecy is the notion that, given an encrypted message (or ciphertext) from a perfectly secure encryption system (or cipher), absolutely nothing will be revealed about the unencrypted message (or plaintext) by the ciphertext. A perfectly secret cipher has a couple of other equivalent properties: Even if given a choice of two plaintexts, one the ...

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