# Tag Info

14

No. The wikipedia article is in my honest opinion misrepresenting this article on a reduced round attack on the SHA-2 family of hashes. Although these attacks improve upon the existing reduced round SHA-2 attacks, they do not threaten the security of the full SHA-2 family. In other words, no collisions have been found in any of the SHA-2 hashes. The ...

7

Well, SHA-1 and SHA-256 are both limited to inputs of no more than $2^{64}-1$ bits; the HMAC architecture itself prepends a logical IPAD (which is 512 bits); hence both HMAC-SHA160 and HMAC-SHA256 are both limited to inputs of no more than $2^{64} - 513$ bits, which is about 2 exabytes. I rather suspect that this is not a serious limitation to your ...

7

In early years of hash function design it was unclear how to choose constants (not only initial vectors), and it was widely assumed that the more random they look, the more secure the function is. There is still not much research in this direction. However, there have been several attacks (rotational cryptanalysis, slide attacks, internal difference attacks) ...

5

The attack which you link to, on ECDSA, is related to the following: the signer computes several values $kG$, for random $k$ values chosen uniformly modulo $n$ ($n$ is the size of the subgroup generated by $G$). One such value is generated for each signature. It is important that the selection is uniform: even small biases can be exploited in order to make a ...

4

You cannot recover the password from the hash. That's not something that password hashes are designed for — quite the opposite: with a proper password hash, the only way to recover the password given the hash is to make a guess and verify it — and the better the hashing scheme, the more costly verifying guesses is. Passwords are used for authentication: a ...

3

Elliptic Curves over binary fields In naive implementation of Elliptic Curves, either $GF(p)$ or $GF(2^{n})$ will be vulnerable to some timing attacks. The paper you provided is on OpenSSL's implementation of EC with $GF(2^{n})$. This implementation uses Montgomery's ladder scalar multiplication, which is in fact very good for making sure that most of the ...

3

SHA-1, SHA-224 and SHA-256 append the bit “1” to the end of the message, followed by k zero bits, where k is the smallest, non-negative solution to the equation l+1+k ≡ 448 mod 512, where l - message length. In second step they use 32-bit words. SHA-384, SHA-512, SHA-512/224 and SHA-512/256 use different equation: l+1+k ≡ 896 mod 1024 and in 2. step ...

3

What you explain in the question resembles SHACAL-2 cipher's forward cipher function, see http://en.wikipedia.org/wiki/SHACAL#Security_of_SHACAL-2. SHACAL-2 is NESSIE accepted way of using SHA-256 as cipher, therefore it has appeared somewhat secure.

2

The following table provides a nice "Comparison of SHA functions". via https://en.wikipedia.org/wiki/SHA-2#Comparison_of_SHA_functions

2

BLS signatures are $\:2\hspace{-0.04 in}\cdot\hspace{-0.03 in}k\:$ bits long, where $k$ is the security parameter, and the probability of a forgery is $\hspace{.01 in}\epsilon$. Pseudorandom MACs (such as HMAC) can be truncated to $L\hspace{.01 in}$ bits, and the probability of forgery (by someone who is outside of the system) will be $\: \frac{\text{# of ... 1 There is vast literature on timing attacks on AES, but to the best of my knowledge no such attack on SHA-2 or any construction that uses SHA-2 (e.g., HMAC-SHA256). 1 Adding more qubits does not increase the computation speed. A quantum computer with 4 qubits does not factorize faster than one with 2. The qubits are the "memory" of the quantum computer. More qubits mean you can factor bigger numbers. If I remember correctly, you need a superposition of$\Theta(N^2)$terms, which means$\Theta(\log(N^2))\$ qubits to factor ...

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