Latest Crypto related questions

Score: 0
mike avatar
Secuirty definion of a ad hoc multi-input functional encryption scheme
in flag

I have to write an essay on the paper ad hoc multi-input functional encryption, and can't understand the security definition. In a nutshell it is a primitive that allow sources to supply encrypted data, such that at any point a dynamically-chosen subset of sources can allow an agreed-upon joint function of their data to be computed by the aggregator.


Syntax description:

aMIFE syntax


Security definition:

enter image description here


I ...

Score: 3
Proof that the Family of Toeplitz Matrices is XOR-Universal
us flag

Definition of XOR-Universal hash functions by Abidin[1]:

A class $H$ of hash functions from $M$ to $T$ is XOR-Universal$_2$ ($XU_2$) if there exist at most $|H|/|T|$ hash functions $h$ $\in$ $H$ such that $(h(m_1) = h(m_2$) $\oplus t)$ for any two distinct $m_1$, $m_2$ $\in$ $M$ and any $t \in T$.

If there are at most $\epsilon|H|$ hash functions instead, for $\epsilon > 1/|T|$, the class $H$

Score: 1
Why use negacyclic convolutions for polynomial multiplication instead of regular convolutions?
pm flag

When multiplying polynomials from $\mathbb{Z}_q[X] / (X^n-1) $, the discrete NTT is used because: $$ f \cdot g = \mathsf{NTT}_n^{-1}\left( \mathsf{NTT}_n\left(f\right) * \mathsf{NTT}_n\left(g\right) \right) $$ However, in virtually all schemes I've seen the negacyclic convolution is used - the ring is $\mathbb{Z}_q[X] / (X^n+1) $ and a trick is used to compute $\mathsf{NTT}_{2n}^{-1}\left( \mathsf ...

Score: 1
Composition of one-way functions and private keys
es flag

Are there any functions f, g and h, such that:

  1. f is one-way and is used to generate an encrypted message c when applied to message m with a public key (c = f(m, N))
  2. Original message m can only be obtained from c in polynomial time (decrypted) if a private key (k) is known
  3. A new encrypted message (c') for a desired receiver can be generated (function g) with the original encrypted message c, public key  ...
Score: 0
Ensure that ciphertext satisfies a fixed secret polynomial
uz flag

Does there exist an encryption algorithm that can ensure that given an input it will generate a ciphertext in a way that will always satisfy a fixed polynomal ?

I can be flexible in the input side but the output side should be fixed to a finite or infinite set of vectors that satisfy the polynomial of degree $d$.

The polynomial is secret. Those who are encrypting do not know that the exact polynomial is ...

Score: 0
Dimitri Koshelev avatar
Protocols of elliptic cryptography, which don't require an indifferentiable hash function (but only a collision-resistant one)?
id flag

Consider an elliptic curve $E$ over a finite field $\mathbb{F}_{\!q}$. Do you know protocols of elliptic cryptography, which require a hash function $H\!: \{0,1\}^* \to E(\mathbb{F}_{\!q})$ such that $H$ is not necessary a random oracle (but only collision-resistant) ?

Score: 1
Schnorr based ZK scheme
cn flag

TL;DR: This ABSOLUTELY does not work and presents a huge security risk. Posting it anyways in case there are other threats I missed or to dissuade any other person who comes up with this idea.

Hi! I’m sort of new to cryptography. I’m starting to venture into ZK schemes. For a small project of mine with which I intend to put in practice what I learnt so far, I came up with a protocol and I’d lo ...

Score: 1
Dimitri Koshelev avatar
What is an advantage of the Charles--Lauter--Goren hash function?
id flag

What is an advantage of the Charles--Lauter--Goren hash function (based on isogenies of elliptic curves) among other provably secure collision-resistance hash functions ? I heard that it is slower.

Score: 1
user19121278 avatar
Does Man-In-The-Middle attack isn't possible when we use reverse of RSA algorithm in Digital Signature?
pk flag

We know that in RSA algorithm Sender A can send an encrypted message to receiver B without any prior exchange of secret keys. A just uses B's public key to encrypt the message and B decrypts it using the private key, which only he knows.

In digital signature reverse RSA algorithm can also be used to sign a message, so A can sign a message using their private key and B can verify it using A's publ ...

Score: 0
1chenar avatar
E382 and E521 edward curves test vector
cn flag

I need test vectors for E382 and E521 edward curves in order to test signature and verification process of a software.

Score: 0
Why is ShiftRow important in AES?
gb flag

I came across a comment about AES 128 without ShiftRow. I want to use this weakness to perform an attack. So far, I get that It possible to divide in 4 independent blocks of 32 bits. So we can launch a attack independently for each block. However, as the key scheduling use all the master key, I don't know if it is possible to make a group force attack with all round.

Currently, I know that I can  ...

Score: 1
xhuliano avatar
Linear cryptanalysis resistance of AES Sbox
cn flag

If you look at the AES Linear Approximation Table (computed for example with Sage) you will see there are many entries with what looks like a high bias of -16 ("absolute bias" scale).

I know AES is designed to be resistant to Linear cryptanalysis. If you agree that -16 is a high bias, then there are 2 (3) options:

  • either the AES Sbox is weak to linear cryptanalysis, but the overall cipher is not thanks ...
Score: 1
What are “weak” and “strong” output-input bit dependencies?
de flag

Section 3.3.5 of the paper “Schwaemm and Esch: Lightweight Authenticated Encryption and Hashing using the Sparkle Permutation Family” (the link to PDF can be found in this page) contains the following text:

Alzette provides very fast diffusion. In particular, all outputs bits depend on all the input bits after 4 rounds, though this dependency can be very weak. After 8 rounds however, we have that  ...

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