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This cipher is called a one-time pad. It is unbreakable ("perfect secrecy") assuming that: The pad (the collection of random bits) really is truly random The pad is never reused to encrypt other messages So, no information can be extracted from $\text{file} \oplus \text{random bits}$. The basic idea of the proof is that an attacker can test every ...


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I unfortunately don't have enough reputation to comment, forgive the answer that is a link to another answer. Your question is explained well in this answer: http://crypto.stackexchange.com/a/12706/17884


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It's not elegant, but the brute force method is to write a program that creates a table of 25x25 digraphs (assuming i=j), yielding 625 rows. I'd also add a column that lists the relative frequency of each digraph (given enough ciphertext you can use that to identify frequent substitutions, as you already have done). You start off with 625! possible ...


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It isn't a good cryptographical PRF (and, to be fair to the inventor, he never claimed it was). Marvin32 starts with a secret state, and processing the message and the state to give a new state, and at the end, outputs the state. However, it outputs the entire state, and the state update process is invertible (if you know the message); hence if you know ...


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The "many attacks" you're referring to, don't exist. There are two main attacks on AES. One needs related keys and drops security level signifantly (to about the half of the bits). You're referring to the other one, the biclique attack on AES. This is the first attack on the full-rounded version of AES (without related keys) that performs better than ...



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