Questions tagged [public-key]

An asymmetric cipher is an encryption scheme using a pair of keys, one to encrypt and a second to decrypt a message. This way the encrypting key need not be kept secret to ensure a private communication. Similarly in public key authentication, the verification key can be public and the signing key private.

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How do I try a timing attack on a public-key implementation on a general-purpose computer?

I'm writing a higher-order function in Haskell for use in public-key algorithms; it works equally well for RSA or elliptic curves. I'd like to test it for susceptibility to side channel attacks. How ...
11 votes
2 answers
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Validating an RSA public key

What kind of tests can be performed on a public key to check if it is likely a valid key? The tests should be relatively fast - i.e. not computationally intensive - and not include modular ...
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Overview over signatures [closed]

When I started to work with signatures, I realized, that this topic is huge. Besides classical signing, there are a lot of schemes based on the idea of digital signatures archiving additional goals or ...
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How does this libgcrypt elgamal decryption work?

Update: The question below was asked before I realized that this is being done to prevent a side channel attack: https://github.com/advisories/GHSA-5p8v-2xvp-pwmc What I am still curious about, is the ...
3 votes
1 answer
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What asymmetric encryption to use that is safe against quantum computers?

i am currently searching for a post-quantum, asymmetric encryption since I need to keep a few files safe for the next decades. AES 256 is what I am using currently, but I would like to leverage the ...
1 vote
1 answer
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Bactracking resistance PRNG - real world usage

I read about bactracking resistance: http://cs.yale.edu/publications/techreports/tr1466.pdf https://arxiv.org/pdf/1810.02227.pdf https://www.schneier.com/wp-content/uploads/2017/10/paper-prngs.pdf ...
3 votes
1 answer
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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 ...
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Using multiple asymmetric keys as backups for one another

I've been thinking about ways to take advantage of multiple asymmetric encryption schemes so that each key could be a backup to the others in case of cryptanalysis of one given scheme. Those public ...
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Are there servers that are oblivious to their own output?

Suppose there are $n$ parties with public keys $pk_1,...,pk_n$. Is it possible that a server S constructs an algorithm $A$ so that for some public random nonce $r$ given as input, S computes some &...
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Is it true that Public keys with even y coordinate correspond to private key that are less than n/2 and vice versa? (Secp256k1)

The question is somewhat complex and directed to clearing things out. Suppose that $n$ is the order of the cyclic group. It $n - 1$ is the number of all private keys possible ...
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QR-PKE not CCA secure

Due to a comment stating "... QR-PKE is secure (CPA)..." I've been thinking of how to prove that it's not CCA secure, and would like to understand whether my proof is correct. Here's the QR-...
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In RSA, are e and d technically equivalent? [duplicate]

In the process of finding RSA key pairs, we first find a e that is relatively prime to φ(n) (where n = p × q), and then find d such that e × d mod φ(n) = 1. Is d also relatively prime to φ(n), or not ...
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Is it possible to execute multi party computation over public ledger?

Let $F(x_1,…,x_n)\mapsto(y_1,…,y_n)$ be some arbitrary computable function. Suppose there are $n$ parties, where each party $i$ encrypt its message $m_i$ with a public key $\mathrm{pk}_i$ and obtain $...
15 votes
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Why do web-services tend to use preshared secret keys for client authentication instead of public keys?

Every API that I have ever signed up with gives you a secret key that you can then paste into your application. They know the key, and so do you. (The one exception may be VAPID for Web Push). Why is ...
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How to modify elliptic curve point?

Good day. How I can modify elliptic curve point, like number modulo ? number example, with unknown privkey 5555555555 : 5555555555 % 2500 = 555 how to get pubkey with privkey 555, from pubkey with ...
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Is it possible to design an algorithm that is based on the xor of the plaintext bits?

Let E be some IND-CPA public key encryption scheme. Given two users with public keys $pk_0,pk_1$ respectively, each user $i$ selects a nonce $r_i$ at random and computes an encryption $c_i = E_{pk_i,...
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In a Diffie-Hellman key exchange Find this key and compute the shared secret key k

Hi I struggling to find the answer of my schhol exam, can anyone help me . In a Diffie-Hellman key exchange the multiplicative group of integers modulo p is used with the parameters p = 59, g = 3 mod ...
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Is there some restrictions on values of p,q,d,e etc in RSA algorithm while trying to encrypt English Ciphertext?

Background: I've seen that the value of plain text should be lesser than p*q as per this slide. I was reading Tanenbaum's Computer Network book the next night, and I saw this thing that I'm not sure ...
2 votes
2 answers
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How to destroy a randomly generated key after using it?

for example, I have an encryption program like this: Input: a message, M; my public key Kpub Step 1: randomly generate a ...
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Is this a secure way to implement E2EE to be decrypted be multiple parties?

Problem I have a central server to store content. A user can create content and control who can decrypt this content. This needs to be secure using E2EE. How another user knows whether to fetch this ...
2 votes
1 answer
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How to encrypt data which never leave the client but can't be decrypted without the server?

Terms: Client: Browser, mobile app or desktop application written using using JavaScript, HTML, CSS and packaged with Capacitor / Tauri. Server: NodeJS based API. Data: Username / password Vendor: ...
11 votes
3 answers
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Is there a signature scheme in which private keys can't be linked to their signatures?

Normally in a signature system, the private key can be used to derive the public key, and therefore verify any given signature signed by that private key. Can we create a system without this property? ...
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Is there any Cryptographic loop function that returns first input?

I want to use cryptographic function that returns the initial input or something related to it like its hash, the function should work like Encrypting some data or its hash, then encrypt the output of ...
4 votes
3 answers
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Is reverse NTRU still secure? (Looking for a signature scheme)

I'm currently prototyping something with the NTRU encryption scheme but I wish to use it in "reverse" -- distribute private keys so anyone can decrypt, but keep the public keys secret and thus only ...
11 votes
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Is there any way to (irrevocably) *transfer* a private key to another person?

Let's say that Alice is the administrator of a group. For each message generated by a group member, Alice uses an administrator's private key ($sk$) to sign it, indicating that this message has been ...
2 votes
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Mitigation of lattice-based KEM decryption failure possibility

Lattice-based PQC KEM has small probability of decryption failure In an offline setting it can be catastrophic despite being improbable. Proposed mitigation: ...
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AKE using Noise_NNpsk2 vs Noise_NKpsk2

I am working on an implementation based on the Disco library, which itself is based on Noise and strobe framework. The goal is to do bilaterally entity-authenticated key agreement with perfect forward ...
7 votes
2 answers
937 views

Post-quantum candidates for asymmetric cryptography with small key sizes

One of the things that I have come to like about elliptic curve cryptography is that the key only needs to be twice as long as the desired security level. That's a very small expansion (I also like it ...
1 vote
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How do I encrypt a bunch of messages by different authors, shared with that group of people?

I'm still getting my head around public/private key cryptography, and I can't quite work out how to ask the right question to get an answer for this problem, but here goes! Alice, Bob, Carol, and ...
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RSA / RS256 Encryption with the public key I have

safe to say I'm a complete beginner when it comes to cryptography... I believe the example output below is some sort of RSA (or RS256) encrypted string, and was just curious whether it'd be possible ...
7 votes
1 answer
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Zero knowledge proof for Paillier addition under multiple keys

Suppose $m_0, m_1, m_2 \in \mathbb{N}$ such that $m_0 = m_1 + m_2$, $m_i > 0$ (none of them can be 0 or lower) Under a Paillier cryptosystem, set $e_0 = E(m_0, r_0)$ for a public key $(g_0, n_0)$ ...
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Why Can't I Use an Nacl Sign Keypair for Encrypt and Decrypt Operations?

I'm aware that the difference between the NaCL sign keys vs the box keys is that the secret key that comes from the NaCL box keypair is the ...
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Computing PGP ed25519 and curve25519 keygrips?

There are public key algorithmic differences for how PGP computes fingerprints and keygrips. For the v4 protocol, fingerprints are not exclusively computed from public keys while keygrips are. RFC ...
16 votes
4 answers
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Is there a cryptographic algorithm that can make a "lottery ticket"?

With public-key cryptography, I know Alice can "seal" a message that only Bob can open. But in that case, Alice knows the message that she is sealing. What if Alice wants to seal a random ...
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A CERTIFIED DIGITAL SIGNATURE paper pg 20 - 25

Reference paper: "A CERTIFIED DIGITAL SIGNATURE" With reference to the image above which is from Page 20 of the attached paper. What is this new protocol that the paper speaks of here? What ...
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Message Hiding Using Keyed Steganography

i would like to know what are the danger can be occur by performing steganography without a key? Please kindly explain to me.
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Will a semi-hyperelliptic pairing be used in real-world cryptography if it is faster than state-of-the-art elliptic pairings?

Let $\mathbb{G}_1$, $\mathbb{G}_2$, $\mathbb{G}_T$ stand for three groups of the same large prime order $r$. I invented a pairing $e\!: \mathbb{G}_1 \times \mathbb{G}_2 \to \mathbb{G}_T$ (with ...
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Is there any good attack model of HMAC?

Are there any good attack models of HMAC? Like how it can be attacked? If there are any possible attacks of HMAC I would be happy to know about it.
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How can a root CA be kept offline and function

Based on many suggestions I have seen around, this, that.etc. Best practice says to keep the root CA offline for very understandable reasons. But how can it be truly offline? Doesn't the root ca have ...
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Check if pubkey belongs to twisted Edwards25519

I want to check if some pubkey belongs to twisted edwards25519 (I guess this is used for ed25519 ?) The problem is that I have in theory some valid pubkeys like: ...
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Proving identity in asymmetrically encrypted communication

Let's assume such a scenario. Person A will broadcast his public key and person B will broadcast his public key. They can now communicate. But let's say that suddenly another person C will write to ...
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KP-ABE Key Generation

In Key Policy Attribute-based encryption if we need a targeted broadcast where the set of attributes are the same for a group of users. It means they all share the same secret key right? Or is it that ...
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RSA with huge ciphertext

I am trying to find the flag from an RSA ciphertext, I am able to get the factors from factordb.com but the given e is not ...
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How to know that MAC isn't modified in ECIES

I am new to ECC but I was wondering, If there is a situation where instead of the ciphertext being falsified, the sent MAC was tampered. How does the receiver verify that the ciphertext is still ...
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Prove a plain text belongs to encrypted data

Given an encrypted (RSA) message and it's original plain text, is there a way to prove that the plain text belongs to the encrypted message ?
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How can JWE support an integrity check given that it uses a public key to encrypt the message?

As far as I know JWE (JSON Web Encryption) supports both integrity and confidentiality. I agree about the confedintiality because only the recepient with a private key can decrypt a message. What ...
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Generating pairs of elliptic $\mathbb{F}_q$-curves isogenous over $\mathbb{F}_q$ such that nobody knows an $\mathbb{F}_q$-isogeny between them

Let $\mathbb{F}_q$ be a large finite field. What if I invent how to efficiently construct pairs of elliptic "cryptographically strong" $\mathbb{F}_q$-curves $E_1$, $E_2$ isogenous over $\...
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Are digital signatures unique for the messages they sign?

Practical implementations of digital signature algorithms (DSAs) employ hash functions to ensure that input is small and of a fixed sized; otherwise, DSAs would be too slow for most real-world ...
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Are RSA keypairs proof of work?

My computer generates a 65536-bit RSA keypair in 106 minutes. Is there a way to generate them faster by some trade-off? Can they be created in bulk, so long as they're able to encrypt and decrypt? Is ...
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Is it possible to prove that an encrypted message was encrypted with some public key without divulging the plaintext or secret key?

I know this seems a bit contrived, but I’m a layperson to cryptographic systems and have been trying to think if it’s possible to devise a scheme where it’s possible for a sender to prove, in a public ...

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