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1500 questions
12
votes
2 answers
Should I use HMAC or KMAC for SHA-3?
I am planning to implement a MAC function for the SHA-3. I read that its latest variant is KMAC. I am confused by the comments on the Keccak website.
It says:
Unlike SHA-1 and SHA-2, Keccak does not have the length-extension weakness, hence does…
ajith
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12
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1 answer
Why doesn't Wang's attack work on SHA-1?
Wang's (et al) differential attack works on MD5, MD4, RIPEMD and HAVAL.
Why doesn't it work on SHA-1?
Peppina
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12
votes
3 answers
Usage difference between x86 RDRAND and RDSEED
Modern x86 CPUs often have the RDRAND and RDSEED instructions for hardware generation of random numbers. I just don't understand the difference between them.
Intel has this document:…
Myria
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12
votes
1 answer
Does SHA-512 leak info about SHA-256?
Does the SHA-512 value of an input leak any information about the SHA-256 value of that same input?
Specifically, if I'm using SHA-512 to derive encryption and HMAC keys from a 256 bit ECDH shared secret (by splitting it into two 256 bit chunks),…
Chris
12
votes
3 answers
Is the number of creatable torrents limited?
Currently, a magnet link containing a 40-digits long SHA-hash value, is assigned to every torrent which is created. Therefore, this hash should be unique to identify a torrent and send the right bytes (packages) to the right people. So therefore,…
MechMK1
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12
votes
3 answers
Is deriving the IV from the password secure?
I came across an encryption scheme to encrypt files with AES-256. You can see the initialization of the decryption routine below:
salt = scrambled_file.read(16)
key_and_iv = OpenSSL::PKCS5.pbkdf2_hmac(password, salt, 50000, 48,…
Jonas
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12
votes
2 answers
Why must an elliptic curve group for ECC have prime order?
What is the deeper reason, a group must have prime order for usage in cryptography?
MichaelW
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12
votes
2 answers
Prove that you have $K$ bytes of memory
Alice has bought a brand new hard disk, $K$ (with $K \sim 10^{12}$) bytes in size. She is very happy about her purchase, and tells Bob about it. Bob claims he also bought a $K$ bytes hard disk. Alice doesn't really trust Bob on this, so she asks him…
Matteo Monti
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12
votes
1 answer
Encoding vs. Compression vs. Encryption
In what ways does encryption differ from proprietary/secret compression schemes and codecs?
ProductionValues
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12
votes
2 answers
How to show that a one-way function proves that P ≠ NP?
According to this, the existence of a one-way function proves P ≠ NP. What is the proof of this?
One way to show this is that if P = NP, then any function is easy to invert. P and NP are about decision problems though, not computation…
Christopher King
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12
votes
1 answer
Minimalist memory-hard function?
What would be a minimalist memory-hard function, reasonably conjecturable to
require $\approx2^k$ bits of memory per running evaluation, $k\approx32$;
require $\approx2^n$ R/W accesses to $2^w$-bit words per evaluation, $w\approx6$ (likely $n\ge…
fgrieu
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12
votes
2 answers
How can we distribute Shamir's secret sharing scheme shares without a dealer?
Let's say $k$ users have shares to a $(k,n)$ secret sharing scheme, and they want to issue new shares. How can they do this without collecting the shares together?
In particular, no set of $k-1$ users (including the new users) should be able to…
Christopher King
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12
votes
2 answers
Definitions of secrecy
I found terms like "forward secrecy", "future secrecy", "backwards secrecy" and "perfect forward secrecy" and I would like to know their definitions and to understand the differences among them.
I found several confusing definitions online,…
M-elman
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12
votes
3 answers
Which algorithms are used to factorize large integers?
Even if RSA decided to cancel the Factoring Challenge, it seems that some teams keep working on it. According to Wikipedia, RSA-768 has been factored in late 2009.
What are the current large integer factorization algorithms and what the mathematical…
Jcs
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12
votes
3 answers
In the Quadratic Sieve, why restrict the factor base?
In the Quadratic Sieve, when factoring a number $N$, many descriptions and most implementations select as the factor base the set of small primes $p_j$ less than some bound $B$ restricted to having Legendre symbol $\left({N\over p_j}\right)=+1$.
Why…
fgrieu
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