# Tag Info

2

Is it necessary to have 50 000 different reducing functions to avoid the collisions? Yes. If you do not have different functions it is not a rainbow table. It is just a table of hash chains which is less efficient, especially for high coverage tables. However, the functions do not have to be unrelated, just different. How do I create those ...

4

Does many:1 mean two different inputs would have the same hash outputs? Yes. This is a consequence of the pidgeonhole principle: as MD5 has a much larger number of potential inputs ($2^{2^{64}}$ or so) than outputs ($2^{128}$), some inputs must lead to the same output, i.e. collide. Cryptographic hashes all have this "limitation", because they have a ...

2

⊕ is a relatively simple operation, so $h(x)$ can be calculated quickly. preimage resistant: No. Given $h(x)$, we can construct $M_1||M_2||...||M_l$ in an arbitrary manner. Since we know h(m), we have a 160 bit string of 0s and 1s. For each 0 in $h(M)$, we can assign an even number of 1s (or all 0s) to that position in the l blocks. For each 1 in $h(m)$, we ...

3

Are there any security issues related to use the same SALT in PBKDF2 for all IDs? Yes, you can build a rainbow table or brute force the ID's. An attacker could build up a table with tokens. Once the table exists the attacker can try all possible ID's until one of them matches. That way the function is reversible and your requirement to keep the ID secure ...

1

Blockchains seem to be a common buzzword these days. And more often than not it is used by people, who don't understand the actual concept in detail. For example, that blockchains are based on assumptions about the distribution of processing power. And when you use it outside the context of bitcoins, you still need an incentive for many people to contribute, ...

0

First, the name keyless signature infrastructure is inherently misleading as this actually has nothing to do with real digital signatures, it is rather some kind of time-stamping service. Now, to answer your actual question: These KSI constructions are solely based on the security of cryptographic hash functions. They do not make use of any other hardness ...

7

Hash + digital signature If the hash is not collision resistant, the attacker can produce two messages having the same hash. They'll request a signature on the first and present the signature on the second, a forgery. When second pre-image resistance is violated, this attack becomes much more severe, since now the attacker doesn't need control over both ...

1

I would just like to know on what basis they can say it is PQC without any NP problem reduction. I believe that the point you're making is assuming that a Quantum Computer could solve any problem in NP that's not actually NP-complete quickly (or, at least, in polynomial time). That's not known to be true; Quantum Computers would be able to solve some ...

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