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Is it possible that a SHA256 hash has the same hex character over and over again?

First of all, the output of SHA-256 is binary and consists of 32 bytes (256 denotes the output size in bits). What you are talking about is apparently the hexadecimal encoding of these bytes. The ...
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Is it possible that a SHA256 hash has the same hex character over and over again?

Yes, it's possible. Given the size of the input space (not actually infinite, but still very, very large), it's also likely, for any given 256-bit value, that several inputs that hash to that value ...
• 285
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Statistical closeness implies computational indistinguishability

A probabilistic distinguisher is still a deterministic function of its input and random coins. So a probabilistic distinguisher trying to distinguish $X$ from $Y$ is equivalent to a deterministic ...
• 13.5k
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Is it possible to construct a PRNG where the output numbers have a certain distribution of hamming weights?

The obvious way to do this is to generate N words, and use logical operations to combine them in a single word such that each bit of the output word is a 1 with probability approximately 0.1 (and the ...
• 148k
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Is there a rule of thumb for ZK protocols?

As usual, choosing the security parameters represents a tradeoff between the security and the efficiency. Therefore, it also strongly depends on two things: how crucial it is that no one breaks the ...
• 20.3k

Is it possible that a SHA256 hash has the same hex character over and over again?

But would that also be possible practically, or do the algorithms check that this is not happening? This is practically beyond anybody to find a 32-$a$'s for SHA-256 without pure luck or one need ...
• 49k

Is this probability negligible?

With much effort, one can get a bound such that I am unclear how tight it is. The bound is non-standard. There is also evidence that replacing your assumption on $Y$ would yield easier bounds. I'll ...
• 13.5k
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Why the definition in $\epsilon$-differential privacy is multiplicative rather than additive？

In short, with this multiplicative definition, it could be ruled out the possibility that an individual's record would be randomly selected and published. Consider a malicious algorithm $M^*$ that ...
• 2,725
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Is there only one formula for the statistical difference between a pair of distribution ensembles?

What we call "statistical distance" in cryptography is called total variation distance by statisticians. So it certainly exists outside of cryptography. I can't speak to its applications within ...
• 13.5k
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Cryptography Engineering - Design Principles and Practical Applications - Chapter 9 Generating Randomness - Section 9.4 The Generator

This section talks about Fortuna, where it uses a block cipher with a 128-bit block and a 256-bit key size. The cipher is used in CTR mode. In the CTR mode, if an attacker can access the internal ...
• 49k

Statistical closeness implies computational indistinguishability

Another way to see this would be to try and upper bound the distinguishing advantage for any distinguisher and relate that to the statistical distance. Edit: Since the following answer is really ...
• 3,338
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The probability becomes more intuitive when one pictures the $t$ persons entering one by one in the room. Before the first person enters, there's no collision/coincidence of birth-date, thus ...
• 142k
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On The Next Bit Test

But this notation is defined (informally) in the first paper. The notation $O(\nu(n))$ is used for any function, $f(n)$, that vanishes faster than the inverse of any polynomial, that is for every ...
• 22.7k
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Calculating minimum number of messages hashed a 50% probability of a collision (Birthday Paradox)

You are approximately correct; they are wrong. Their answer calculates the chance of matching a particular value i.e. hash inversion. To see this $k$ tries have a $(2047/2048)^k$ of failing to find a ...
• 24.1k
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