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I take it that your question is: How do people determine if a cryptosystem is weak? Well there are two types of people who need to do this as you pointed out: the ones who made the system and those who want to break the system. If the process is symmetric, then all we need is that the process is not linear. That is why AES won - it is long and ...

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For cryptanalysis, the usual three-point method applies: Write down the problem. Think real hard. Write down the answer. And that's about all that can be said generically. The methodology of a cryptanalyst is about the same as that of researchers in any other science. The core of the daily work of a cryptographer is to read, read, read all the papers. ...

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If the attacker knows the encryption method, then assuming it's a decent algorithm it won't help them break the cipher in any meaningful way. Cryptography is designed and analyzed under the assumption that the attacker knows everything except the key; among other reasons, it's incredibly hard to keep the attacker from knowing the system, while a key is much ...

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It depends what you're worried about, and what you are really trying to protect. If each of these slices is individually important (say a 1 MB list of credit cards), then you're basically just encrypting each chunk by itself. The total strength of protection for each chunk is just the size of the key you used for that chunk (modulo strength/weakness of the ...

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What you describe (figuring out which cipher was used, given only the ciphertext) is a type of distinguishing attack. Modern ciphers are generally highly resistant to such attacks: the ideal cipher produces output that is indistinguishable from random noise.

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