# Tag Info

4

A long message is a message that, when padded, is longer than the block size of the hash function. That means that the hash function has to process the message in parts and keep track of state somehow, which may allow for attacks. Such attacks would not apply to messages shorter than the block size, and may additionally require a large number of blocks to ...

4

Without the specific reference I can't be sure this is what you are talking about, but generally a "long message" attack is a way to defeat second preimage resistance with less complexity than expected. It uses a time-space tradeoff to find a second preimage with complexity $2^{n/2}$ for a $n$-bit hash function (normally you would expect $2^n$). In the ...

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The twist attack is best explained in Fouque et al's paper. While the (quadratic) twist of the curve $E : y^2 = x^3 + ax + b \in \mathbb{F}_p$ is indeed of the form $E^t : y^2 = x^3 + d^2ax + d^3b \in \mathbb{F}_{p}$ for nonsquare $d$, you can also think of the twist as the set of points $(x, y)$ in $E^2 : y^2 = x^3 + ax + b \in \mathbb{F}_{p^2}$ where $x$ ...

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The classic standard assumptions (such as DDH, CDH) are not parametrized and always have constant size (are static). Consequently, the assumption when used in a reductionist proof is independent of any system parameters or oracle queries and only related to the security parameter. In contrast, non-static ($q$-type) assumptions as already mentioned by ...

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After reading this paper, it looks like a $q$-type assumption is simply one which is parameterized over the value $q$. For instance, the $q$-DBDHI (Decisional Bilinear Diffie-Hellman Inversion) assumption is that, given $(g, g^x, g^{x^2}, \ldots, g^{x^q})$, it is difficult to compute $e(g,g)^{1/x}$, where $e$ is the pairing operation. This produces a ...

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