# 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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### Why is it impossible to find the private key from the public key?

From what I understand, based on the article A Beginner’s Guide: Private and Public Key Cryptography Deciphered, the public key is generated by performing $n$ tangent plus mirroring operations from ...
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### In public key cryptography, how many keys are required for secure communication between n parties?

In public key cryptography, how many keys are required for secure communication between n parties? In my view the answer should be $n^2$. Reason: There are ‘$n$’ Parties. Every Party has One (1) ...
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### How exactly are GPG keys (and prime numbers inside of GPG) mathematically related?

I know that the keys are somehow mathematically related, and I know that they're somehow generated via prime numbers, but how exactly are they related? I realize that it'd probably be best for me to ...
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### Cryptographic equivalent of family coat of arms

As a layman when it comes to cryptography, I have recently been asking myself if there was a cryptographic equivalent of a family code of arms. I'm thinking of something asymmetric, that is future ...
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### Welcome To Pyca Cryptography [on hold]

Cryptography includes both high level recipes and low level interfaces to common cryptographic algorithms such as symmetric ciphers, message digets,and key derivation functions.For example,to encript ...
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### Will publishing two or more public keys of the same RSA private key cause a security risk?

I want to make an end-to-end messaging platform where everyone is identified with a unique random private key. Everyone uses other peers' public keys to identify and send encrypted messages and verify ...
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### How does RSA public and private key structure look like?

So I was reading this wiki about the RSA algorithm and I read this article to understand it better. My goal was to create a simple program that would generate private and public keys. I got to the ...
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### DH prime size required to force an attack of $2^N$ steps

Why the size of a DH prime $p$ should be about 6800 bits long to force an attacker to perform $2^{128}$ steps to attack the system? How is this relationship 6800-128 established?
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### Convert a plain public key to PEM format [closed]

I plan to generate an EC key pair using P-256v1 from a trusted application and export the public key to Normal OS. The public key will either be in plain format or have none (only key hex). The ...
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### PKI Multiple Samples start to expose Private Keys?

My understanding is that using a PKI, public/private key pair is generally secure to send message to people. That is, encrypt a message using the recipient's public key so they use their private key ...
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### Private and Public Keys

I have a very basic understanding of encryption and the encapsulation process, but for the life of me I can't grasp how public keys and private keys work, how they're made, and how they're exchanged. ...
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### What is the actual result of a Logjam's DH attack?

Does a Logjam attack calculate a group of probable Diffie-Hellman private keys for a user and then try them one at a time to see if it can decrypt the message - or does it directly calculate the one ...
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### How to calculate e if we know n,p,q,m,c? [duplicate]

If we know n, p, q, and we have an encrypt oracle, which means we can input any plaintext and we'll get its ciphertext, and here p is smooth, which means the factors of p-1 are very small, is that ...
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### ECC with 512bit compatible curves

I understand that given solutions for solving a discrete logarithm problem are on the order of 𝑂(2𝑛/2), ergo, 256bit private keys based on 25519 or secp256k1 have an effective bit strength of ...
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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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### What is the difference between forward secrecy and key freshness?

Is all random private key that generating a unique session key is both forward secrecy and key freshness?
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### OpenSSL ECDH setting peer's public key in C [migrated]

I'm trying to integrate ECDH using OpenSSL in my C-SDK (which we will refer to as client) which is running on Ubuntu and needed some help regarding how to set the peer's (server) public key on the ...
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### man-in-the-middle attack on text-book RSA PKE

I am attempting to solve the following problem: I know the following: 3 messages are being sent between Alice and Bob, all messages are encrypted with the known public key $(d,N)$: Alice sends ...
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### The goal, the method, and the interface of the signcrypt primitive.

Some time ago, I proposed making the site more educational by teaching correct cryptographic programming. The proposal had had somewhat good reception, but was met with cold ice as there had been ...
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### How does the KeyGen of Merkle's improvement of Lamport's OTS work?

In his paper [1] on page 17 and 18, Merkle proposes an improvement on Lamport's OTS by only signing the 1's in the message in combination with a checksum of the amount of 0's in the message. I get the ...
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### How to prevent Public Key from being replaced entirely?

I am using RSA to sign my license file using Microsoft CNG API. I am signing the license file and sending the file with the <...
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### Characteristic of Public Key?

Is Public key used directly to encrypt a message or it is used to derive other keys ? Can we decrypt a message with same public key using which it was encrypted ? So far I understand, as PKI is based ...
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### Half of any bitcoin (crypto) public key - (public key half) is possible

I found a topic on bitcointalk Public key x and y == Double(Half of the Public key x and y) half any public key is possible how that possible , in crypto there is subtraction and multiplication ...
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### Guidelines for cryptographic key generation

I was wondering whether you know can point me to some general (basic) principles/guidelines one should follow for generating cryptographic keys? I have looked at NIST 800-133, but was hoping for some ...
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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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### Identifying a bad public key

The great thing about public key cryptography is that anyone can generate a keypair, keep the private key secret and publish the public key anywhere they want. This is used in CAs where an ...
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### Why isn't ElGamal a symmetric-key scheme?

I was asked about this question by a friend. He considers that Alice and Bob share a secret key s=g^(xy). So why isn't it considered a symmentric-key scheme? ...
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### Why Nonces and timestamps are used in Public key authority?

why the nonces(N1 and N2) and Timestamps(T1 and T2) are used in Public key Authority? which of them prevent replay attack?
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### Importance of the order of public/private key application to a signed encrypted message [duplicate]

Let's say two users (U1, U2) each have a private key they keep to themselves, and each broadcast a corresponding public key to the world. Let's then say that U1 wants to send a signed encrypted ...
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### How can a message encrypted with the public key be decrypted with the private key?

I've been reading about encryption and have a basic understanding of the concept. What I don't understand, however, is how a calculation with one key can result in a number that, through calculation ...
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### is there any good implementation to the RSA in arduino ? c language [migrated]

I need a good implementation to the RSA algorithm that works on Arduino mega with key size 1024. the code will run on Arduino ide. the project idea simply is an android app send an encrypted message ...
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### How to exchange a common key to a group of person using Elliptic-curve Diffie–Hellman (ECDH)? [duplicate]

In ECDH, when two persons want to share private keys, they first select a point $G$ on the elliptic curve and after that, each of them picks a random integer $a$ and $b$, respectively, and multiply ...
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### Decentralized / Distributed Private Key Generation between Untrusted Parties?

I found an interesting concept in this paper, page 13, (Link to the paper) called "Decentralized private key generation", as follows: "Decentralized private key generation – Multiple Enigma nodes ...
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### Share secret non-interactively in a verifiable way

In an application, I need to share a secret (random number) with a Group of known receivers over a public channel (a Blockchain) but each receiver needs to be able to check that the others received ...
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### Why public key has two parts in my secure messaging client similar to signal

I am working on a Golang code similar to Signal protocol. I need to modify it. I am confused on tripartite Diffie-Hellman handshake part of code, i.e. why public key has two separate parts as compared ...
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### How to find at least one private key from a large list of compressed public keys secp256k1

Not long ago I saw a discussion on the Bitcoin Talk forum: https://bitcointalk.org/index.php?topic=5060735.msg50736695#msg50736695 Please give advice and working methods? Is it possible to find at ...
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### Minimal secure index of quasi-cyclic codes for code-based cryptography

It is well-known that keys (generator matrices) of code-based cryptography are very large for its practical usage. To reduce them scientists propose to use families of quasi-cyclic codes. I remind ...
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### How do pairings behave on G2/twist points off the prime order subgroup?

$\newcommand{\F}{\mathbb{F}}$ Consider the ate pairing defined on a curve $G_1 = E(\F_q)$ and $G_2 = E'(\F_{q^r})$ where $E'$ is a twist of $E$ with the twisting isomorphism defined over $\F_{q^r}$. ...
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### Can you compress an elliptic curve private key in half?

According to this, a $n$-bit key offers about $n/2$ bits of security. That got me wondering, can you compress the key in half? At first blush, no, because the key is essentially a random number, and ...
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### How to encrypt sensitive files in a business application? Is it needed? [closed]

I'm currently working on a business Java application, and we store sensitive files related to our users. What is the appropriate approach to store them securely? Is it viable to encrypt/decrypt all ...
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### If H(m) = 0 for some m, how can a DSA signature be forged?

If we know for some message $m$ that $H(m) = 0$, how can we forge a DSA signature with only the public key? I got that $g^s*r = (g^x)^r$ where $x$ is the private key, but that's one equation with 2 ...
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### ElGamal encryption and signature using same keys

In ElGamal scheme we have message $M$; $p$, $g$ and $y=g^x \bmod p$ as public key where $x$ is unknown private key. Encrypted message $(c,d)$, where $c=g^k \bmod p$ and $d=M \cdot y^k \bmod p$. ...
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### cryptographically signed streaming data

On a high level the question is: how does one cryptographically sign streaming data? Here is the context: a number of people are continuously streaming data to me the data is public and does not ...
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### RSA: why does $m^{ed}$ equal the original message?

Trapdoor functions are defined as that a secret key reverses the function. It seems to me more that it causes a cycle to repeat, similar to how $n^k \bmod k$, when $k$ is a prime number, equals $n$, ...
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### What attacks does future secrecy protect against?

Consider messaging between 2 parties. A sequence of messages are exchanged between the parties using encryption. We consider an attacker that has at a minimum a log of all the (encrypted) messages ...
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### What's wrong with RSA and OpenSSL?

We all know that signing a document is to encrypt its hash using signer's private key. https://commons.wikimedia.org/wiki/File:Digital_Signature_diagram.svg I've been searching the web for days, ...
There are many kinds of fully homomorphic encryption scheme by using boolean circuits. And the plaintext space $\mathcal{P} = \{ 0,1 \}$. If there is a -bit FHE scheme, we can construct a FHE scheme ...