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If the file has been crafted deliberately to survive this form of damage then yes you should be able to recover your data. There are many quite simple methods from adding CRCs to replicating the data multiple times. There are other possible routes to recovery. If for example the file was an ASCII text file then it may be possible to recover something close ...

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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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There are several algorithms available which can attack a playfair cipher. Hill climbing might be one option. Basically it starts with a random key (assuming it's the best one) and decrypts the cipher. The resulting clear text is scored using a fitness function. Then small changes are applied to the key and if the resulting clear text of the modified key ...

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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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