# Tag Info

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Dingo13, the answer is that P and S boxes are effectively two halves of the same thing. This is the reason people confuse the two. Despite the Wikipedia plagiarism, e-sushi's S-P network diagram is an excellent example of the reason for needing both. The object of a cryptographic function is to alter the input in an unpredictable way, be it for an ...

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Using Vigenere as an added security measure is like adding an a4 plain printing paper on your head during a rainy day. It might soak some water, but you will get wet in the end. Use a well made umbrella (Or a modern well tested encryption method). So yes, it could be cracked (and relatively easily) while you are asleep. Other than historical and hedonistic ...

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The term you are looking for is Modular Arithmetic. In the case of 1535, if it is indeed a combination of 3 values ranging 0 to 25, you do the following: 1535 mod 26 = 1 (1535 - 1) / 26 = 59 59 mod 26 = 7 (59 - 7) / 26 = 2 The set of values that generated 1535 is 2,7,1 (c,h,b?), which can easily be verified.

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Well, the previous answers assumed that you could ask for a single plaintext that consisted of multiple characters (possibly including the entire alphabet); I'll view it from the aspect of a plaintext consists of a single symbol. If the multiplication operation within the affine operation is integer multiplication (modulo the alphabet size), then it ...

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I think the 10100 is a typo and should be $10^{100}$ as shown here The period would be something along the lines of how long until the byte stream repeats. For example if the byte stream were "ABCDABCDABCD" and so on, then the period would be 4. For security you want a large period so that you can encrypt large amounts of data.

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Assuming CTR mode is used properly (in particular, neither $IV_1$ nor $IV_2$ is a prefix of the other, which if they're the same length just means they're different), knowing $(M_2,C_2)$ does not help an attacker find $M_1$. Vulnerability to such an attack would imply vulnerability to a chosen plaintext attack; instead, CTR has the IND-CPA property, which ...

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It probably refers to the Index of coincidence, or more accurately the un-normalized index of coincidence, referred to in the Wikipedia article as "kappa-plaintext".

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This all depends on the IVs. If they are independently generated, the IVs will not only be different (so $IV_1 \neq IV_2$), but also their sequences will not overlap with overwhelming probability. In that case, then everything should be fine, so $C_2 = E(K,(nonce,IV_2))$, and $C_1 = M_1 \oplus E(K,(nonce,IV_1))$. However, if they are reused (so \$IV_1 = ...

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