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This type of problem is known as anonymizing data, and it has fairly standard solutions. The obvious way is to use a Format Preserving Encryption method; that is a secret key method that has a fairly arbitrary domain. Because Alice is the only one who needs to be able to encrypt and decrypt, she can generate the key locally, and never distribute it. If we ...


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It is unfeasible with newer CPUs to just count instructions, as newer CPUs can do multiple per cycle, and have multiple cores and likewise. Cycles per byte is the usual way to measure performance these days. Of course, to make it as fair as possible and comparable to others, the code is only ideally run on one core, turboboost and hyperthreading is turned ...


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I don't think there is a name for this special kind of property, but it is a clear hint for polyalphabetic substitution ciphers. It is a special kind of polyalphabetic substitution cipher. The first alphabet is a normal random key, while each successive alphabet is generated by a one-character right shift of the previous alphabet. As a result there are as ...


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Apparently there's at least one real-life example of a block cipher with equivalent keys: TEA has a few weaknesses. Most notably, it suffers from equivalent keys—each key is equivalent to three others, which means that the effective key size is only 126 bits. As a result, TEA is especially bad as a cryptographic hash function. This weakness led to ...


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The number of possible permutations of a block cipher are $2^n!$ where $n$ is the block size. A permutation maps all $2^n$ possible input blocks to $2^n$ possible output blocks. A key, with key space $2^k$ selects one of them. Although that's a huge number of keys, it is dwarfed by the amount of possible permutations. Now it's not by definition impossible ...


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In cryptography it is common to reason about the probability of an event in the probability space of all the random choices made (i.e. the random bits generated) during an algorithm's execution. So, in this description, "over the random coins of HGD" means the probability is computed over the probability space defined by the random bits used during HGD ...



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