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Wel, yes, but you cannot use the key $k_1$ for anything else because knowledge of $k_1$ would mean that an attacker can simply calculate $k_2$. If an attacker can find a direct relation between parts of the output then the function is of course not pseudo random anymore. So although it is possible it seems pretty useless to me. Even if you would not ...


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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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Yes, this could be done. It would be easy to implement and use this in a way that would be horribly insecure (e.g. with too short a passphrase, and not enough key stretching), but if used carefully, it could even be secure. Basically, what you'd do would be: Generate a secure passphrase, e.g. a sequence of randomly chosen words. This can be done ...


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By using the definition of $n$ bits of full entropy, NIST is abstracting away from the definition of a NRBG (or TRNG). They are basically trying to establish a minimum requirement for the quality of the random number generator, without going into the specifics on how this can be achieved. Basically this is NIST's way of saying: if we specify $n$ bits of full ...


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"Entropy" is more accurately defined, in cryptography, as "that which the attacker does not know". For instance, suppose that every day you take all rates at the closure of the New York stock exchange, and hash them with SHA-256. The resulting value is very unpredictable (otherwise you could become very rich), so, from a "physics" point of view, there is a ...



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