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2 votes

Security of 128-bit hash function with salt

We assume you have a secure hash function $H: \{0,1\}^{128} \rightarrow\{0,1\}^{128}$. Using this you want to construct a different hash function $H' = H(m \oplus s)$, where $m$ is your plaintext and $...
  • 1,672
3 votes

Debug bcrypt iterations with a static salt

You can't calculate a bcrypt hash from a bcrypt hash with a lower cost factor. Few password hashing algorithm allow a cost factor increase without knowing the password, and bcrypt isn't one of them. ...
3 votes
Accepted

Debug bcrypt iterations with a static salt

Your expectation is incorrect. The output isn't just the intermediate state that could be used to continue processing. It's a specifically-formatted string according to https://en.wikipedia.org/wiki/...
  • 972
1 vote
Accepted

HKDF-Expand max output length

Yes, there are no known bad interactions from this. Kind of. There are no known attacks on HKDF just from using the same PRK to generate a lot of keying material. If there was a problem already at 64 ...
  • 103
0 votes

Which of the following is a reason to publish files' hashes?

Common Scenario: I do it all the time with Ansible. You download an Apache web server file httpd-2.4.54.tar.bz2 You want to make sure the fire you downloaded was not tampered with You go onto ...
9 votes
Accepted

Does "SHA-256/192" use different initial values from SHA-256?

No, it is just the truncated as mentioned in NIST SP 800-208 $\operatorname{SHA-256/192}(M)$ $T_{192}(\operatorname{SHA-256}(M))$, the most significant (i.e., leftmost) 192 bits of the SHA-256 hash ...
  • 44.2k
0 votes
Accepted

API design that maximizes the potential of parallel and tree hashing

Data Availability This is probably the least of the concerns. If data is available at a (much) slower rate than the hash algorithm implementation, then that's not the bottleneck. System Load This is a ...
  • 7,103
1 vote
Accepted

Is there a hash function that is semi-two-way?

Good off-the-shelf password handling software does almost exactly that: After hashing the password with the salt(*), the output of the algorithm is a string of text stored in the "hash" ...
  • 5,374
2 votes

Can a cryptographic hash function that outputs a c-membered subset of the n-membered set?

Yes, take any cryptographic hash function $f$ whose output space is greater than $m:=\binom{n}{c}$ which is the number of possible subsets. To map the value $x$, we reduce the output of $f(x)$ modulo $...
  • 12k
4 votes
Accepted

Merkle–Damgård construction - the bigger input, the longer time to compute hash?

That's right, and you've just stated the obvious. The processing time of Merkle-Damgaard-based hash functions are proportional to the size of the input (unless the input is too small). That's also ...
  • 7,103
2 votes
Accepted

Create a control hash string from different sources, is there a difference, advantage or disadvantage in comparison when using this ways?

Assuming that there is no difference in files and strings (we will use $s_1$ and $s_2$), we can look at the hasing speed and pre-images and collision attacks. We assume + as concatenation summation ...
  • 44.2k
1 vote

How easy is it to identifiy the key when knowing a certain number of different AES-256/Fixed Nonce encrypted long-integers

should be used like passwords(known only by few individuals) Yes, that would work. must always be the same for the same integer True for single block encrypt using AES and using the full output. ...
  • 86.5k

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