# Tag Info

11

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 ...

5

Password strength is typically measured in bits of entropy, or in layman's terms, the amount of "true randomness" in the system. This is measured by the process of how the password is generated rather than by the number of bits in the output. It's a simple extension of Kerckhoff's principle: assume your attacker knows your process, and the only information ...

1

One problem not mentioned here is that CRC collisions are a certainty. If you were using a cryptographically secure hash, you would never encounter a false positive where both solutions were possible. In this scheme, every 256 messages would yield identical CRC values, and your different versions would be indistinguishable. You might be able to "stutter" ...

4

This started as a comment to @Poncho's fine answer, and grew over the 600-char limit. Point is: a careful choice of the definition of V2 messages can keep some the existing capabilities of the original CRC to always detect some kinds of errors. Foremost, we are interested in short error bursts (where all bits in error are within a small number of ...

3

If there was a better known way than brute force, I suppose someone would already have made a paper about this (or lets this be secret to use it for attacks – but then this person wouldn't enter in such a competition). So it looks like just brute force. Why are these people better than you? Some guesses (and most likely it is a combination of these): They ...

4

Since the output of the configuration of Skein is 1024 bits, we would expect to get 512 bits correct just by random hashing. So the question is, what is the probability of getting 640 bits correct? From that we can figure out how long it would take for that to occur. There are ${1024 \choose 640}\approx 4.16\cdot 10^{292}\approx 2^{972}$ ways this can ...

1

CRCs are not cryptographically secure. If you need cryptographic security, replace the CRC with a message authentication code (MAC). If you don't need cryptographic security, then your question is off-topic for Crypto.SE and you should probably flag it to ask the moderators to migrate it to Computer Science.SE.

8

First of all, if your goal is to keep the garbled messages to "once every hundred years", well, you already don't meet that goal, even before the change. With an 8 bit CRC, a random change has a probability 1/256 of being accepted; hence if your wireless network has a transmission error at least once every three months (which, to me, sounds like an ...

2

I wouldn't even go so far as to say that a good hash function must have "as few collisions as possible" as you state in your question. The identity function has no collisions if we restrict the domain to be the inputs having the same size as the digest. But it's clearly a lousy hash function. To be "good" as a hash function is hard to define (which is ...

4

If a hash function is a random oracle, which is about as perfect as can be expected for a hash function, then we actually expect a lot of collisions. If the hash function output is in a space of size $N$ (e.g. $N = 2^n$ for a "$n$-bit output") then collisions are expected, on average, when about $\sqrt{N}$ distinct inputs are hashed (see the birthday problem ...

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