I read the Blake2x paper: https://www.blake2.net/blake2x.pdf

It says Blake2x can be used to build a "DRBG" (CSPRNG): https://csrc.nist.gov/glossary/term/deterministic_random_bit_generator

"An algorithm that produces a sequence of bits that are uniquely determined from an initial value called a seed. The output of the DRBG “appears” to be random, i.e., the output is statistically indistinguishable from random values. A cryptographic DRBG has the additional property that the output is unpredictable, given that the seed is not known. A DRBG is sometimes also called a Pseudo Random Number Generator (PRNG) or a deterministic random number generator."


I want to know if the initial state (state size) of Blake2x is "enlarged" when hashing, because I didn't understand this notation:

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Despite the internal state of Blake be 256/512 bits, can Blake2x be used to build a stream cipher (CSPRNG/DRBG) with security more than 256/512 bits given a seed with a larger size?

If I have a source full of entropy (like a high resolution photo) and I hash with Blake2x to a key of 8192 bits per example, will I get a key material with this size?

Can some Blake2 enthusiast answer my questions? (I tried to contact one of Blake2x authors, Jean-Philippe Aumasson, but I gave no response).

  • 1
    $\begingroup$ Why do you care about "more than 256 bit security"? Does your attack model include adversaries that can harness the entire output of the sun to attack your cipher? $\endgroup$
    – poncho
    Dec 20 '21 at 15:23
  • $\begingroup$ are you considering this key size for the PQ-PKC? $\endgroup$
    – kelalaka
    Dec 20 '21 at 15:34
  • $\begingroup$ @poncho I want to keep my secrets forever, I hold material about secret societies. $\endgroup$ Dec 20 '21 at 23:06
  • $\begingroup$ @kelalaka I want to write a disk encryption program that will use keys sizes like this. $\endgroup$ Dec 20 '21 at 23:07
  • $\begingroup$ crypto.stackexchange.com/q/1145/18298 $\endgroup$
    – kelalaka
    Dec 20 '21 at 23:14

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