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Jun
29
comment What stops the Multiply-With-Carry Random Number Generator from being a Cryptographically Secure Pseudo-Random Number Generator?
@e-sushi: That's not the same thing, because a secure NLFSR generates its state update via one function, and its output via a different function. This allows the generator to hide its internal state (which is necessary for a secure PRNG). Something like MWC, on the other hand, uses the same function for state update and output, meaning that the output exposes the internal state directly. Nonlinearity can be useful, but is not directly on point here.
Sep
15
comment What stops the Multiply-With-Carry Random Number Generator from being a Cryptographically Secure Pseudo-Random Number Generator?
Wikipedia has a reasonable explanation of what "security" means. Note that no RNG that "work[s] by keeping a certain number, say k, of the most recently generated integers, then return[ing] the next integer as a function of those k" can possibly satisfy the next-bit test, because anyone who's seen its k most recently generated integers can predict its entire future output.
Jul
27
comment Is truncating a SHA512 hash to the first 160 bits as secure as using SHA1?
A caveat to the "security implications" section: if the plaintext values are guessable (or chosen from a limited set), an attacker will be able to guess-and-test possible plaintexts. For example, if you hash the State field of an address database, there'll only be 50 distinct hash values, and an attacker won't have much trouble figuring out which is which. Similarly, if you hash the Name field, and the attacker wants to find out if "John Q. Smith" is in your DB, they can hash that and look for a match.
Jul
15
comment What prevents continued hashing of a key from being used as a cipher when xored with plaintext?
Point 3 is a killer. Encrypt something that starts "<!DOCTYPE html>\n" (with a 128-bit hash), and the message is trivial to crack.
Feb
1
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Dec
2
comment How to generate a list of unique random strings?
Note that the first two options can be truly random (if they're based on a truly random source); the last is only pseudo-random (at least once it gets past the key size of the cipher).