# 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 to solve this Baby Bleichenbacher Attack?

I am trying to solve this problem from https://toc.cryptobook.us/book.pdf. I am having trouble with this question : (Baby Bleichenbacher attack). Consider an RSA public key (n, e), where n is an RSA ...
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### How are public and private keys generated and used for encryption and decryption in a lattice based cryptosystem?

I've recently become quite interested in lattice based cryptosystems, and I wish to understand them more deeply. I have only a rudimentary understanding of the shortest vector problem (SVP), and its ...
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### How to know if a public key has been created based on the ECDSA algorithm?

Suppose in a network, the identity of users is their public key, which is generated based on the ECDSA algorithm. That is, to create a valid identity, a user must generate an ECDSA public key and then ...
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### Zero knowledge validation to check if private element is in a set hidden on a central server

I am trying to determine how to apply ZK proofs to the asymmetric scenario below. Say there is a list of 5000 secret elements on a centralized web server. Users are trying to guess what those 5000 ...
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### How do certificates help?

I am reading a networking book by Mike Meyers, and it says that a certificate is a file that contains A public key, and A signature (cryptographic hash of the public key, encrypted with the private ...
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### minimal public-key authenticated encryption protocol

One party (master) wants to send data to another party (slave) over an insecure channel using public-key encryption and signature schemes such that: master is authenticated, data is confidential, ...
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### How to evaluate efficacy of new public-key cryptosystems

Suppose I had a new public-key or key exchange protocol. How do I objectively evaluate it so as to determine if it is worth sharing with the broader community? Whenever developing a cryptosystem, it ...
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### What are Key Size requirements (rather than modulus size) for different Asymmetric Algorithms for 112-bit security?

A lot of writeups, books & webpages say that to get 112 bit security (i.e $2^{112}$ steps), you need to use RSA or DH with 2048 key size or ECDH with 224 key size. In reality, I think what is ...
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### Compressed Address public key [closed]

Is it possible to get the x, y of the compressed public key? I have decompress it and naturally it gives the xy of the decompress public key. I need the xy coordinates of my compressed public key . ...
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### How can you use ZK-proofs and public key signatures in this situation?

Let us say that we have 3 entities: an Issuer I , a user/prover P and a verifier V. ...
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### Can two ciphertexts that decrypt to the same plaintext be statistically "distant"?

It might be a little dumb: I think it should be possible, if I encrypt a plaintext using the same public key twice, it should be possible to end up with two ciphertexts that for whom the statistical ...
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### Is it secure to sign a JWT using RS256?

I have implemented an authentication scheme using JWT with assymetric keys (RS256). The idea is that (assuming some microservice-based acrhitecture) the authentication service will sign all JWTs with ...
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### Finding the private key with the transaction signature [duplicate]

I have two ETH transactions (both belonging to the same address) that both have the same r value in the transaction signature, is it possible to extract the private key from it? Details of both ...
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### Authenticate people online with simple public / private key scheme or similar

How can I ensure that person X on website A is the same person who contacts me? Here is my use case. On website A I post message asking username X to contact me. Someone send me an email - how do I ...
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### Can we force a chosen ciphertext to be decrypted to a chosen plaintext while controlling only $e(=3)$ in RSA? [duplicate]

I have bumped into this challenge from a well known CTF site. I don't want to make a reference to it because I don't want this to be a hint for anyone. And also to avoid giving out the source code of ...
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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 ...
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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 ...
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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 ...
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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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### 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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### 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 ...
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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 ...
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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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### 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: ...
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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 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 ...
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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 ...
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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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### 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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### 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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### 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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### 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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### 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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### 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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### Can a private key be reverse engineered when a 3rd party has a lot of my digital signatures? [duplicate]

I am wondering how secure it is to share digital signatures with a 3rd party (signed using one private key). For example, let's say I'm signing a million different messages with my private key and ...
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