# 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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### Find factors of N given RSA public key (e, N) and private key (d)

I am having some problems solving the following problem: find factors of N given RSA public key (e, N) = (11, 459703599527) and private key d = 125373708962. I calculated k = ed - 1/ N = 3, and Φ(n) = ...
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### How to break RSA when $q = e^{-1} \bmod p$?

This problem was posed during a recently ended contest. I am given a value for n and e. e = 65537. n is a 2048-bit number. p is a 1024-bit prime number. q is the modular inverse of e mod p. That's ...
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### Does a list of discrete log equations reveal information?

Given public generator $g$ of some cyclic group, a secrets $x\in Z_q$, and public pairs $(a_1,b_1),...,(a_n,b_n)$ (where $a_1,...,a_n$ are selected at random from a big set), and prime p, that ...
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### keyring encrypted with public keys

I would like to publicly store a list of public keys of recipients in a way that only the individual recipient ( who holds the private key of a that referenced public key) can see that he is ...
1 vote
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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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### How do you use a PQC Hybrid Shared Secret in Practice?

In https://tools.ietf.org/id/draft-stebila-tls-hybrid-design-03.html, they define (many other sources do too) hybrid shared key exchange as “Hybrid” key exchange, in this context, means the use of ...
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### Is Regev’s public-key encryption with $sk$ chosen from $\{0, 1\}^n$ circular secure under CPA security?

I thought maybe this is true with something like the following reduction (if we assume for contradiction that it is not circular secure): For $A$ to 'break' CPA security, let $C$ be the 'collaborator' ...
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### Can a user set his public key without knowing its corresponding private key? [closed]

I'm wondering if in public key infrastructure (PKI), a system user be able to set his public key without knowing its corresponding private key. Can this be done?
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### Can functional encryption encrypt and decrypt negative integers?

I want to use DCR-based functional encryption for encryption and decryption purpose. However, I'm unsure whether DCR-based functional encryption can support negative integers. Is there any ...
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### Can asymmetric encryption be used in HMAC, and still ensure the data has not been tampered with? [closed]

Suppose I want to send a message, but not privately; I want everybody to see it, even an attacker in the middle. I would do this by appending a public key to the start of the data, which could be used ...
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### Do we want to allow/Have we allowed parallelization (e.g GPU programming) to enter the cryptographic field? What are the consequences?

With the term GPU programming, I'm referring to highly parallelizable computing in general. Lastly, I have built a bit of a background in cryptography. So I have started to wonder if/where GPU ...
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### What happens if the Miller-Selfridge-Rabin-Test fails

MRT is a probabilistic test and even the deterministic version relies on the correctness of the Riemann hypothesis. When the test fails and I use a non-prime number in e.g a public key encryption ...
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### Are Encryption, Key Exchanges and Digital Signature the application of asymmetric encryption

Reading the wikipedia entry on asymmetric cryptography, will I be wrong to conclude that there are 3 main broad category of application for asymmetric cryptography? Mainly: encryption digital ...
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### Asymmetrical scheme: insecurity concerns of saving a hash of a hash of a password

please verify or explain how to do this properly. I'm letting a user create keys from the client through a secure server. I ask the user for a password on the client, then send the hashed password to ...
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### Difference signature / asymmetric encryption (PQC)

The NIST is currently trying to select new standards for post-quantum cryptography. The two main categories for the candidates are "Public-key Encryption and Key-establishment Algorithms" ...
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### In RSA, What does gcd(e,phi) != 1 means? Why always choose e = 2^n +1 not 2^n?

Recently I have few experiences with Questions in RSA which e is 2^n instead of 2^n+1, and that leads to gcd(e, phi) is not equal to 1... Won't this make the private key impossible to get? Is the ...
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### Is it possible to calculate the modular inverse of a secp256k1 public key?

I know that it wouldn't be possible to use the extended Euclidean algorithm, since it would require the ability to divide a public key and calculate the remainder. I was wondering if there were any ...
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### Security definition for IND-CPA of public key encryption

In the security game between the challenger and the adversary for the security definition of public key encryption, the challenger creates and gives the public key pk to the adversary. The adversary ...
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### What does Euler's theorem have to do with RSA?

In RSA we compute e (encryption key) and d (decryption key) $\bmod phi(n)$ and not $\bmod n$, so how come when we get the keys and encrypt and decrypt we use $\bmod n$ not $\bmod phi(n)$ using the ...
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### Signature delegation without secret keys

Scenario: have an entity A that cannot hold any secret keys. A concrete example would be: an application that needs to be open sourced and cannot be modified. In order to send any signed messages, it ...
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### Paper that specifies how to define number ranges inside the ECC with varying equations

I am looking for a textbook or published paper that provides specific information on how to configure an ECC. I came across it several years ago and now cannot find it. Does anyone know the source? ...
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### Does this encryption scheme have any major vulnerabilities?

Recently I asked a question of whether there is any cryptosystem that satisfies a number of properties (read the properties). Continuing to the promise I gave there, this is my attempt to construct it....
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### Is there a public-key, "deal-less", all-or-nothing, "secret-length message" cryptosystem or some easy way to derive it?

I want to make an ecryption algorithm that is secure in, well, really many ways, which is hard I see, so I came up with some ideas of how to implement it using some primitives that I know and I ...
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### Why do we need to use Asymmetric cryptography if Diffie-Hellman solves the key exchange problem of symmetric cryptography?

I am new to cryptography and I cant get my head around this issue: If symmetric cryptography is faster then asymmetric and given that Diffie-Hellman key exchange algorithm allows you to exchange keys ...
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### Is there a discrete log challenge?

RSA challenge is well-known and it has a wiki page. Is there a discrete log for $\mathbb F_p$ where $p$ is Sophie-Germain prime?
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### Is possible to cipher a 64bit message into a 64bit message using public key cryptography?

I'm looking for a non-invertible bijective function mapping a 64bit value into another 64bit value. I can't use a hash because it isn't bijective. Could this be done with public key cryptography ? The ...
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### Does Man-In-The-Middle attack isn't possible when we use reverse of RSA algorithm in Digital Signature?

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 ...
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### Sending encrypted message without public key from recipient (elgamal)

assume Bob and Alice use Elgamal encryption scheme. Alice wants to send Bob a message, but does not know Bobs public key. Is there a way for Alice to find out Bobs public key by receiving multiple ...
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### Isn't an asymmetric cipher (like RSA) algorithm sufficient for all basic needs, when speed is irrelevant?

Why I care: I want to implement some secure sessions for communicating over internet and since I am a complete amateur in this and don't want to spend a lot of time learning about cryptography or ...
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### Simple scheme to publish data with a private key

The goal is for Alice to send an encrypted message to Bob. Neither Bob nor anyone else should be able to decode the message. Alice should be be able to decode it, when all data is shown to her. ...
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### How to use symmetric encryption on 1on1 and group chat messenger?

Hi everyone so currently I'm trying to learn about encryption to build secure messaging app (Mobile-app, flutter based). I want the app to have 2 messaging features which are 1 on 1 messaging and ...
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### Classical vs Quantum-Safe Algorithms and Protocols / Application Approach

Various proposals are being explored for X509 V3 certificates in a Post Quantum Cryptography (PQC) world. Currently, these include just having a certificate for classical and PQ, having a hybrid ...
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### Is this AES GCM + asymmetric schema secure?

I want to use the asymmetric encription offered by a tool to encrypt my files and I would like to know if the following encryption process works, regardless of perhaps not optimal use. Generate a <...
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### ECDSA private key recovery

I have a bunch of signatures (1000) signed with ECDSA secp256k1 curve. I can verify all of them with the same public key. I have studied attacks are performed against ECDSA signatures using known MSB ...
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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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### Can you derive the public key from a PGP encrypted message without knowing the message content?

I am working on a system to transfer short messages while obfuscating the intended recipient. In essence, it combines many messages encrypted using PGP, and periodically publishes a file containing ...
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### What does prevent a hacker to calculate signature from message and public key without using private key? [duplicate]

I am talking about the process in the image: Everyone is saying this process is safe and and what I am claiming is impossible, but common sense says different.
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### Questions on "A CERTIFIED DIGITAL SIGNATURE" Pg. 19

Referenced paper here. The above excerpt is from Page 19 of attached paper. I have a few questions. y = F^9(x) is equivalent of F(F(F(F(F(F(F(F(F(x))))))))) ? The excerpt says that this allows us to ...
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### Sharing RSA private keys using key exchange algorithms like Diffie–Hellman Algorithm?

Me and my friend would like to login to an SSH server using the same private RSA key. However, we don't want to transmit the key over the internet, for security. I am thinking if it's possible to ...
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### RSA: Obtain private key exploiting badly generated public key

I have to solve the following problem: What I have: $n$, a 2048 bit number What I need to find: $p$ and $q$ such that $n = p\cdot q$. What I know: With $p_1$ the first half of $p$ and $p_2$ the ...
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### Online/offline times of Key Distribution Center and Certification Authority

In comparing the merits of a Key Distribution Center or KDC versus a single root certificate authority public key infrastructure or PKI, is it possible for the KDC to be online at all times whereas ...
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### Discrete Logarithm Based algorithm

The private (secret) key in DL (discrete logarithm) based algorithms is uniformly selected from the group Zq*. This private key is then used to compute the public key. Could the opposite be done, for ...
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### ElGamal-based BBS proxy re-encryption implementation?

are there any available tools/libraries that implement the idea of EIGamal-based proxy re-encryption scheme shown below? Preferably in Golang. Thank you! Source of this picture: https://www.cs.jhu....
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### Public-key/asymmetric encryption where you can only leak the decrypted message by leaking your password

A bunch of friends are using public-key encryption to send encrypted messages to each other using an open public forum. I.e. each friend has a public key (which you can use to encrypt messages for ...
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### Is it possible to have a Hierarchical Deterministic KD for ECC with child key leak not impacting parent key?

From what I understand, in BIP 32, the knowledge of the parent public key and the child private key provides the parent private key, in a non-hardened path. Indeed, it's only a matter of substracting ...
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### Best way to encrypt sensitive data on server with HSM and symmetric keys

I need to store sensitive data (like customer photos) in a SQL database in the most secure way in case of security breaches. The data won't be accessed by the clients, only to internal processes that ...
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### Can Bob and Alice do an authenticated Diffie–Hellman key exchange if Bob only knows the hashsum of Alice's key?

Tor vanilla bridges look like this: Bridge x.x.x.x:1234 9DD03662B50FEDBF6F8D5630CB86D7E8CE4F4432 It's only the IP/Port and a hash of the key. Can Bob and Alice do an authenticated Diffie–Hellman key ...
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### Lamport Diffie One-time Signature

I am going through the Lamport Diffie One-time signature. I am having a hard time understanding How can long messages (greater than 100 bits) can be mapped into short messages (100 bits) by a one way ...
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Consider an elliptic curve $E$ defined over a finite field $\mathbb{F}_{\!q}$ with a fixed non-zero $\mathbb{F}_{\!q}$-point $P$. For simplicity, let the order of the $\mathbb{F}_{\!q}$-point group \$E(...