# All Questions

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### 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 ...
32 views

### Encryption scheme that requires fewer keys for decryption than for encryption

I want to attempt creating a decentralized dead man's switch, so I'm looking for an asymmetric encryption scheme, with the following properties (ideally), or something close to them: There is a group ...
42 views

### Theory Question with Enigma

I have been reading a bit about how the Enigma machine was cracked in WW2. There was also this wonderful post which highlighted a lot of useful information. Let's assume I know everything about how ...
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### Effect of longer key on DES security

I am reading a book on cryptography and the author states that one of the complaints of the research community was that DES key length was chosen to be too short. I am trying to depict how DES would ...
86 views

### ECDSA signature verification checks

From Wikipedia: Check that $Q_a$ is not equal to the identity element $O$, and its coordinates are otherwise valid. Check that $Q_a$ lies on the curve. Check that $n*Q_a = O$ Verify that $r$ and $s$ ...
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### What is the intuition behind the strength of unstructured symmetric cryptography?

Consider a single round of a cryptographic permutation, what is so special about it that lacking some bits of information that either get mixed into it as a subkey or omitted at the end (sponge ...
68 views

### Can zero-knowledge proof be used to determine if another person knows a certain movie with a twist ending?

Suppose I want to talk with a co-worker about a movie called "The Twist Movie". I know the movie contains an interesting twist, and bringing up the movie in a discussion about twists in movies might ...
56 views

### Lattice Based Cryptography domain

Some cryptosystems operate on the domain of the form $\mathbb{Z}_q[x]/\langle x^n-1\rangle$ and others operate on $\mathbb{Z}_q[x]/\langle x^n+1\rangle$. What's the security impact of the two forms?
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### Are there any cryptographic methods which use multiple cyclic groups?

For some cryptographic methods you can construct them. e.g. elliptic curves (product of two cyclic groups) or Diffie–Hellman (can be product of n-cyclic groups). But they have no usage because at a ...
56 views

### Do people sign my subkey?

So, I've generated my GPG key pair. Created a subkey for signing and a subkey for encryption. Exported the whole thing, removed my master key pair to a secure place, re-imported only the subkeys. Now, ...
46 views

### Small(er)-lane Keccak-f: impact and usage

Keccak defines a family of hash functions, by building a sponge out of a permutation Keccak-$f[b]: \{0,1\}^b \rightarrow \{0,1\}^b$. This permutation function is parametrised using $b$, which is the ...
51 views

### Subexponential algorithms that apply only one of factoring and discrete logarithm?

Shor (quantum polynomial), Number Field Sieve (subexponential), Pollard rho (square root) all have both factoring and discrete logarithm over $\mathbb F_p^*$ variants. What are the subexponential ...
140 views

### CVP over $\Bbb Z_{q}$ - is the problem still hard?

I'm reading about the CVP problem, and all the papers I've read so far handle the case where the CVP matrix and vector are over $\Bbb R^{n}$ (or over $\Bbb Z^{n}$), and the distance is a real number. ...
40 views

### Are there any more ways to validate a security proof except peer review?

Are there any ways better than peer review to validate a security proof? Are there any ways to make your security proof easier to validate; using a simulator based proof instead of a game based proof? ...
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### Schnorr protocol is witness-hiding?

Regular 3-steps Schnorr protocol is a proof of knowledge system for discrete logarithm. It's honest-verifier zero-knowledge, but not full zero-knowledge. My question is, is it witness-hiding? (I guess ...
51 views

### Does weak hardcore bit(s) implies strong hardcore bit(s)?

It is well known that weak OWF implies strong OWF by concatenating several evaluations of weak OWF (see e.g. here), where weak OWF is defined as $\exists$ poly $Q$, $\forall$ PPT $\mathcal A$ ...
217 views

### OAEP Security: PKCS#1 v1.5 vs SHA1 vs SHA256

I'm looking at two major RSA encryption standards: PKCS#1 ver. 1.5 RSA OAEP The second one can use different hashing functions to create a hash of encoding parameters and then verify the hash at ...
68 views

### What is the probability equation of rotational cryptanalysis on modulo multiplication?

The answer in this question defined how to calculate the probability of rotational cryptanalysis on modulo multiplication $\odot$. This paper defined an algebraic equation of how to calculate the ...
31 views

### If curve bn256/bls12 support the isomorphism from $G_2$ to $G_1$?

Is bn256 or bls12 a type-2 pairing-friendly curve? As Dan Boneh said here While in many pairing instantiations this ψ exists naturally, in some instantiations it does not. However I can not find ...
63 views

### On average conditional min-entropy

The average conditional min-entropy of X given Y, $\tilde H_\infty( X | Y)$, measures, roughly speaking, the amount of randomness that is in $X$ given as side information $Y$. (for the formal def, ...
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### What is the difference between discrete-then-gaussian and gaussian-then-discrete?

In lattice cryptography, we always face the probem of discrete gaussian sampling. To the beginners, it is a bit complex. However, gaussian sampling from a continous space is much easier to understand, ...
123 views

### How does the key agreement process take place in Virgil E3Kit SDK for end to end encryption?

I'm using Virgil E3Kit SDK to implement end-to-end encryption in my App. Their E3Kit SDK is very effective and not too hard to understand, but I still don't understand how does the key agreement ...
34 views

### Are there any hash-based multisignature schemes?

Are there any hash-based signature schemes which would let two (or more) people sign the same message without increasing the size of the signature linearly? For my purposes, it is fine if the scheme ...
68 views

### Bounds on failure probability for universal exponent method?

The following definition is from Trappe and Washington, "Introduction to Cryptography with Coding Theory". Given a number $n$ and an integer $r > 0$ such that $a^r \equiv 1 \pmod{n}$ for all ...
80 views

### Crack a polyalphabetic cipher given a pair of (plaintext, ciphertext) encrypted by it

The original question only states that a classical cipher is used, and I am going to articulate 1) why I think a polyalphabetic substitution cipher is used AND 2) my attempts so far. The Question <...
65 views

### Impossible to construct collision resistant hash function from one way function

[Simon 98] showed that it is impossible to construct collision resistant hash function from one way functions in a black-box way. I read the paper but barely understood it. Is there any source, where ...
32 views

### EC non-shared cryptosystems - different group for every party

Efficient Identity Based Parameter Selection for Elliptic Curve Cryptosystems by Arjen K. Lenstra contains a proposal for a non-shared elliptic curve cryptosystem. Every party chooses its own field ...
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### Is there a bilinear map on a non abelian group or non cyclic group?

I've recently been studying a pairing map on cryptography. In usual definition, a pairing map is always defined on the cyclic group G. Is it possible to construct a bilinear map on a non-abelian group ...
53 views

### 1-digit MAC with error-catching properties?

The well-known Luhn check digit (used in credit-card numbers) is a public method to append a check digit on the right of a decimal number, so that any 1-digit alteration and any exchange of two (...
48 views

### Equivalents of Yao's Xor lemma to rounds, or other hardness amplification methods?

Simple question: I just learn the existence of the great Yao's Xor lemma (see a quick sum-up at the end of this post). I'd like to use a similar argument, but instead of a simple function, I've a two ...
50 views

I'd like to avoid sending user passwords over the wire. Would the following challenge response protocol be secure (served over TLS)? I know this is similar to SRP. Sign-up Client takes password and ...
120 views

### Argon2 parameters concurrent access

I am trying to figure out the best parameters for Argon2 for password hashing. I have read the RFC and the recommendations they put in it. So I follow up the recomendation on the paper depending on ...
45 views

### Is uneven DES keybit use exploitable?

Question: Is there any cryptanalytic leverage to be had from the fact that some of the 56 "raw" keybits of DES are used more & less often than others? Observation: over the course of the 16 ...
52 views

### Orignal Krawczyk's HKDF vs latest NIST SP800-56C

I've noticed that the original HKDF in rfc5869 defines a feedback loop. So the pseudo-code is something like: ...
49 views

### EC-ELGAMAL message mapping

I have been able properly set up an EC-elgamal protocol by using algorithms available in an IP that I have developed. Everything works fine, except for the fact that I haven't been able to completely "...
### Finding maximal $n$-affine subset
We obtained $l$ vectors $B_i$ of $c$ bits $b_{i,j}$. These are an altered form of vectors $A_i$ where the last $n$ bits of each $A_i$ are an affine function of the other bits of that $A_i$. We want ...