# All Questions

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### Elliptic Curve Blind Signature Implementation

I have seen this prior post: Elliptic Curve based blind signature implementation Currently I'm sizing up how difficult it would be to attain Elliptic Curve Blind signatures for an application I'm ...
82 views

### Are there any real-world E-voting systems in use with the Paillier cryptosystem?

There are a lot of theories of Paillier cryptosystem with references to e-voting. Are there any real-world E-voting systems in use with the Paillier cryptosystem?
94 views

### Can cryptographically useful pairings only be used with elliptic curves?

As far as I understand one big advantage of ECC is that we can use pairings on the group of torsion points of the curve. I was wondering if it is possible to construct pairings from general finite ...
285 views

### How did G.H. Hardy's work contribute to today's public-key cryptography?

I know that Hardy's work in number theory was used by Clifford Cocks in 1973 to develop the basis for public-key cryptography. What specifically was this work, and how is it used today in ...
445 views

### Can convergent encryption be turned into deterministic authenticated encryption with HMAC?

If you take a convergent encryption algorithm and replace the hash $H$ used to derive the key with HMAC-H, keyed with a secret key $k'$, does the resulting algorithm provide you with deterministic ...
234 views

### Explanation of part of a visual cryptography algorithm

I have been working on a project involving visual cryptography and I am stuck with the following problem. My question is related to this paper, AN IMPROVED VISUAL CRYPTOGRAPHY SCHEME FOR SECRET ...
236 views

### IES: What security has the asymmetric primitive to provide?

I think most of us know the notion Shoup introduced of KEM/DEM (Key Encapsulation Mechanism / Data Encapsulation Mechanism) which is used for example by the (famous) ECIES, where the key is the hash ...
131 views

### Anonymisation resilient to key leak

Problem statement Elbonian citizens have been issued a card holding a random $B_j\in\{0,1\}^b$, $0\le j<2^n$, $b\ge n+20$ (representative example $b=64$, $n=28$). The habit has grown to use this ...
157 views

### Using machine-learning techniques for data-dependent operations in ciphers

From 'Methods of Symmetric Cryptanalysis' by Dmitry Khovratovich, The data-dependent operations are one of the most controversial design concepts. We say that an operation is data-dependent, if it ...
206 views

### As a cryptographer, what are the things I should care about in my implementation of pairing functions?

As a beginner in cryptography, I do not know anything about different pairing types more than their names. So far, I know these names: Ate pairing, tate pairing, eta pairing, and r-ate pairing. I am ...
164 views

### ECIES: Purpose of optional shared information?

According to Wikipedia the ECIES algorithm has two optional shared information $S_1$ and $S_2$. They are used as follows: Generate a random shared secret $Z$ according to ECIES, which will never be ...
60 views

### What is the restriction on $k$, for the $k$th composite residuosity problem to be hard?

The paper “Residuosity Problem and Its Applications to Cryptography” considers the exponent to be an odd integer. When $k = 2$, it is called the quadratic residuosity problem (mod $n$, where $n$ is ...
129 views

### Implementation Attacks on Hashes

So I am familiar with attacking implementations of block ciphers via side channel attacks, cache-timing attacks, etc. What implementation attacks are there against hashes or hashed based functions (...
200 views

### understanding the proof of knowledge

Recently I've been reading the paper “A New Family of Implicitly Authenticated Diffie-Hellman Protocols”. It's very hard for me to go further. Especially when it comes to the proof of knowledge. ...
198 views

### Feasible way to check n-dimensional equidistribution of PRNGs

I am currently gathering some test methods and test suites for random number generator qualities, and am a bit stuck at finding something feasible to test for n-dimensional equidistribution. As input ...
284 views

### Secure Secret sharing

I'm trying to come up with a new way to do oblivious transfer that is faster and requires less computation than existing methods. The basis of my method is shamir secret sharing. Below is an example ...
491 views

### Using the same private key for two ECC key pairs

Let $(d_1,Q_1)$ and $(d_2,Q_2)$ be ECC key pairs over two different elliptic curves (say NIST P-224 and NIST P-256). According to the Elliptic Curve Discrete Logarithm Problem (ECDLP), if the private ...
255 views

### Obfuscating point-like functions

There are standard schemes for obfuscating a point function; I'm wondering if we know how to obfuscate a slight generalization of a point function. I'll elaborate more precisely. Definition 1. A ...
703 views

### Key expiration policy for 3DES / TDES / Triple DES

I have a system that signs plain text messages using a message authentication code (MAC) encrypted with 3-key Triple DES. The short message is used on connection to establish a session key, so it ...
160 views

### Is MITM possible after key exchange phase done successfully in RSA?

Is MITM attack theoretically possible after public/private key pair exchange is done successfully. Say Alice and Bob have genuine public keys of each other. Is MITM possible further during ...
405 views

### Storing password or derived key in keychain?

Currently I am developing an application that stores and reads encrypted data. The data is encrypted with AES and the actual AES key is derived from the users password (and some nonce) with PBKDF2 ...
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### A confusion about linear span of modified de Bruijn sequence

Recently i'm reading "Cryptographically Strong de Bruijn Sequences with Large Periods" . In the section 2 2.1 Basic Definitions and Properties , property 1 says ...
361 views

### How hard is a known prefix hash preimage attack on SHA-2?

Suppose the attacker knows $X, Z$ such that $H(X || Y) = Z$ If bit-length(Y) < 60 then a brute force attack is possible. What if ...
433 views

### How can Alice and Bob safeguard their message exchanges against replay attacks?

Assume Alice and Bob communicate over an insecure channel using one-time perfectly-secret encryption together with one-time secure message authentication code. Say Eve has the ability to eavesdrop and ...
183 views

### Lattice-based cryptography prone to side channel attack?

Is lattice-based cryptography still prone to side channel attacks? What are some mitigation strategies, if any?
477 views

### Nonce reuse resistance

I read this article and I think the approach outlined there is very interesting for one of our use case. We use ChaCha20 Poly1305 (via Sodium ...
190 views

### Generating random vector for Full Homomorphic Cryptography

The site below explains that part of doing homomorphic encryption, you need to generate a vector of random numbers that have the property that its dot product against a randomly generated bit vector ...
2k views

### Effective key length of Two-Key Triple-DES

What's the effective key length of Two-Key Triple-DES, for some (possibly several) reasonably well-defined and sensible definitions of effective key length, say assuming attack using ample chosen ...
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### Attack on Weierstrass Elliptic Curve

I have a naive question(as non specialist in this field). While reading Weierstrass Curve description,I found that it turns into 2 periodic tori on 2D complex plane. Is is it possible to create ...
82 views

### Error-Correction capabilities of encryption?

This is motivated by this question about the recovery of (corrupted) encrypted files, and in particular the statement (in the answer): But If I know the algorithm and the key and I make a custom ...
53 views

### Provably secure way of expanding permutations

Gimli is a 384-bit permutation which makes use of an internal 96-bit permutation which works on columns. Every 4 rounds starting from the 1st a "small swap" is performed and every 4 rounds starting ...
88 views

### How do byte-sliced AES implementations work?

While I understand the principle of bit-slicing, several papers mention byte-sliced AES implementations (see e.g. Homomorphic Evaluation of the AES Circuit and Fast Implementations of AES on Various ...
139 views

### Security of ECC over finite fields of characteristic $p\approx2^{50\pm10}$?

What's the security of Elliptic Curve Cryptography over finite fields of word-sized characteristic $p\approx2^{50\pm10}$? We are talking about $\Bbb F_q$ where $q=p^k$ for some suitable $k$. ...
155 views

### Is this distributed random oracle scheme safe?

This question comes from an issue raised in another question: Non interactive threshold signature without bilinear pairing (is it possible)? Is the proposed random oracle model safe when trying to ...
38 views

### Difference between group key agreement, group key sharing, group key distribution and group key establishement

I am currently doing a survey on group key, and throughout my readings, I stumbled on these different terms: Group Key agreement, Group key Sharing, Group key distribution, and Group key establishment....
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### Bitslice DES decryption

I would like to implement fast DES decryption using Bitslice technique. Without bitslice DES technique, I have already done decrpytion in this source code by changing the for loop from 15 to 0. In ...
101 views

### Which is the smallest safe elliptic curve (bit-length)?

At https://safecurves.cr.yp.to/ some elliptic curves are listed which passed certain security test. The smallest bit-length of a safe curve listed there is 221 bits. At wiki page discrete logarithm ...
In the context of ECC. There's an EC point $P$ which is supposed to be a known power of another known point $G$ (generator). That is: $P = [k]G$ (in additive notation) This should be verified on an ...