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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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What is the difference between $\bmod{p - 1}$ and $\bmod p$

I have a doubt in my research work, can anyone tell me; What is the difference between $\bmod {p-1}$ and $\bmod p$
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Temporal or spatial digital signatures

Digital signatures allow authentication of content based on a secret held by the signing entity. Are there any existing schemes, proposals or even services for letting "location" or "time" sign the ...
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Store the public key and private key [on hold]

i want to implement digital signature scheme in my form sign up in my web, and i read all PKCS from PKI but it made me little confused. i have many questions, where i store my public and private key ? ...
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ElGamal variant

I came across this problem, while currently reading "Introduction to Modern Cryptography" by Katz and Lindell. I am new to crypto and just trying to go through the book and solve the exercises, ...
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Can POS devices really generate random numbers?

I am doing an implementation of a system designed by a payment company and I am a little skeptical about the way they have designed the end to end cryptography. The system is as follows: There are ...
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Simple but secure method to share secret (128 bit AES key) though an untrusted relay

I am creating an end-to-end encrypted group messenger, and am looking for a way for online members of the chat to a arrive at a shared secret that can be used as a cryptographic key. This will ...
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Security of the Needham-Schroeder public key protocol after a minor adjustment

I'm preparing for a computer security exam by going through some past paper questions. And I came across this particular one that I could not answer: We have the Needham Schroeder Public Key Protocol:...
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Are compressed pairings used for Barreto-Naehrig curves in practice?

In 2009 Galbraith and Lin wrote the article "Computing Pairings Using x-Coordinates Only" https://link.springer.com/article/10.1007/s10623-008-9233-3, where they proposed to compute pairings on ...
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Derivable encryption key - BIP0032 parallel

I wish to find an asymmetric encryption algorithm that supports key derivation, BIP0032 style. Meaning that I have some SEED [PRIV] and I give someone some public data [PUB], then given new public ...
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How many keys in a Hybrid Cryptosystem?

If symmetric cryptosystems have $C^2_n$ keys, and asymmetric systems have $2n$ keys, how many does a hybrid system have? This was in an online quiz from school Company A is considering to adopt ...
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Is it acceptable to add a setup algorithm in the public key encryption?

I saw in the paper How to Use a Short Basis: Trapdoors for Hard Lattices and New Cryptographic Constructions at page 29 that key generation algorithm of PKE can use a common random matrix $A$. Is it ...
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Verifying valid public key and finding private key? [duplicate]

A naive user of RSA has announced the public key $n = 2903239, e = 5$. Eve has worked out that $n = 1237×2347$. Verify that the public key is valid and explain why the private key is $d = 2319725$. [...
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Fail to Sign/Verify signinature in C# [migrated]

I am trying to use the .Net RSA functions to sign a Hash, but when i try to Sign the hash and then verify the Signed string it turns out false... Is this the wrong place to ask? (Is this more of a ...
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Does Elliptic Curve Integrated Encryption Scheme (ECIES) provide IND-CCA2 security?

I am looking for a faster alternative to RSA with OAEP as a IND-CCA2 public key scheme. Elliptic Curve Integrated Encryption Scheme might be a candidate, but I am not sure if it provides IND-CCA2 ...
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How to create a private key using $n,e,d,p,q$ where $n$ is prime

Someone has incorrectly created a public/private key pair where $N$ (modulus) is a prime number. This makes $p$ and $q$ trivial as they they are $n$ and $1$. $d$ is solved from $d \cdot e = \bmod (...
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zero knowledge proof of encryption

I am trying to see if there is a way to prove that a ciphertext c was encrypted under a given Public Key, Pk, without revealing the plain text message m.
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Digital Signature Verification failed using SHA256withRSA in Python [migrated]

I am trying to validate the digital signature with given certificate files for the offline aadhaar KYC verification application. This instruction is given in the documentation for the verification. ...
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Rolling Code via Encrypted Index vs Pre-Generated Keys

I am planning on designing a system that needs a password to be operated, using a rolling key. Now I am facing two options, as far as I am concerned: Having an index saved, which will be incremented ...
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Definition of Short Authentication String

I am studying for my cryptography final and I passed by the following term: short authentication string. Please, can anyone explain it to me, thank you very much.
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Comparable or partially homomorphic public key derivation for signatures?

Are there any public key signature schemes that can be compared blindly or partially homomorphically based on the private key without knowing the private key? Example: let's say I derive a public key ...
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Concept for a RSA “repeater”. Is it sensible?

I have been using RSA signed/encrypted mailing a lot recently. Naturally, I wanted to use RSA mailing also on my phone, not only on my computer. However, I feel uneasy having my private key on my ...
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Digital signature

I learned that a digital signature is encrypted using private key and is decrypted using public key. How does the verifier gets the public for verifying the signature? If a person has to request ...
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Public key on Server Key Exchange Generation vs Public key on Server's Certificate

To understand the distinction between TLS 1.2 and TLS 1.3. I am stuck in the past understanding for TLS and the current reference I am studying: As I know certificate goes with owner's public key, ...
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Creating multiple “public” keys from one private key

Is it possible to create a public key out of a private key, then create another public key from the first public key. And treat the first public key as a private key (So you have two levels of private ...
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RSA using 2 as a public exponent

I'm failing to see why 2 can never be used and what weaknesses would be associated with doing so. There's a similar question asking why it has to be in the form of $2^n$+1 but why not $2^n$
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Pseudonymous publication of a series of texts online when a bad guy is expected to join in with fakes: will this approach to PGP verifiability work?

Alice wishes to publish under a pseudonym a series of texts online. She expects the texts to circulate, and she will not include any way of contacting her. Bob will not know the identity of the ...
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Why ECDSA has its form?

According to Wikipedia, if Alice wants to sign some message, she computes $s = k^{-1} (z + r d_A)$ then sends $(r, s)$ to Bob. I don't understand why they use this particular formula $s = k^{-1} (z + ...
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Where does one store 3rd-party Public Keys

So, I've just started looking at the subject of Cryptography and am working through Stephen Haunt's Practical Cryptography course on PluralSight but have a question that doesn't appear to be covered. ...
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280 views

SSL - encrypt with private key and then with public key?

Say there are 2 sides that wish to communicate: side A and side B. Let's say we are looking at side ...
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1answer
48 views

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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RSA engine with inaccessible private keys - susceptible to any attacks?

We are going to integrate some hardware accelerator for RSA into our next system on chip. This chip can accelerate the core RSA operation, i.e. modular exponentiation $y=A^x \mod(N)$. The private key (...
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Format of hybrid crypto envelope structure?

From posts including the accepted answer to How to encrypt file with RSA and AES that anyone with RSA key can decrypt them? hybrid crypto (AKA envelope encryption) a GPG-encrypted file has an ...
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Why does DH-EKE require that public keys be indistinguishable from random?

The introduction to SPAKE pre-authentication states: Diffie-Hellman Encrypted Key Exchange (DH-EKE) is the earliest widely deployed PAKE. It works by encrypting the public keys of a Diffie-Hellman ...
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Send content to owner of gpg public key, nested content symmetric encryption

If I want to encrypt a text content file using a symmetric algorithm like AES, is there a standard format gpg will expect, where it can detect a symmetric key (encrypted with recipient gpg public key ...
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Performing a dictionary attack on RSA/ECB with no padding

I have the exponent $e=2^{16}+1$ and modulus $n$ (154 digit number) of an RSA public key along with the ciphertext (64 bytes) encrypted using the same key with RSA/ECB and no padding. I am required ...
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Patterns flaw to sign a counter with public key encryption protocol

In modern asymmetric encryption protocol, like secp256k1, are there any flaws if you want to sign a counter? i.e: use a private key to sign from 1-n is that any chance make n+1 easier to guess?
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How does the process of creating a new secure Elliptic Curve look like?

I'm especially curious about the technique djb would have used to come up with his Curve 25519. Say I have already written down my goals, such as - Twist Secure, Speed, Side Channel resistance, etc. ...
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For elliptic-curve cryptography, does a 256-bit key imply that $x$ and $y$ are each 256-bits or 128-bits?

In the wikipedia article, the claim is made that "256-bit elliptic curve public key should provide comparable security to a 3072-bit RSA public key". Since, in ECC, the public-key consists of a point $...
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A private key with multiple public keys?

I'm trying to design a wallet, where any number of public keys can be handed out. Say Alice hands out the public keys to receive messages. She doesn't want others to be able to link all of the public ...
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Why does the Node crypto library do Diffie Hellman this way?

I was sifting through the Node Crytpo library and I came across their Diffie Hellman utility class. Their class implements a generateKeys function that, in their ...
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Size of group for Elliptic curves vs RSA for equal security

For my research, I would like to compare the efficiency of a scheme when instantiated with Elliptic curves and RSA. So, I would like to know a "latest" comparison (as of 2018) on what group sizes of ...
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Detect MITM with hashed session-key — Is my protocol secure?

I have the following setup: An app ("client") wants to communicate securely with a device I created ("server"). The client has the public key of the server (and a hashed password) preinstalled. I use ...
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RSA How to select a value K such that $e d = 1 + k \varphi(N)$ holds

I am learning RSA cryptography. The part I am stuck on is understanding how k and the public exponent $e$ is selected. Given the formulas; Decrypting: $c^d \bmod N = (m^e)^d \bmod N$ Which is equal ...
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Do standalone Oblivious Transfer (OT) Protocols exist?

Are there any Oblivious Transfer (OT) protocols that don’t rely on asymmetrical encryption, public-key encryption or key-exchange? I’m starting to wonder, as all the OT protocols I know of (and can ...
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1answer
46 views

Is the only use for the private key of a root certificate signing certificates issued by it?

A root certificate can be used to issue intermediate certificates. The private key of the root certificate is needed in order to sign any intermediate certificates. However, after that, we only need ...
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What is the relationship between attribute based encryption (ABE) and access control?

So if possible could someone tell me or at least recommend a book.
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What are the different use cases between an HMAC and digital signature? [duplicate]

I understand that both an HMAC and digital signature are used to check the integrity and authenticity of a message. Further, I understand that a digital signature is non-repudiatible. What I do not ...
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Is a digital signature of use if you don't also encrypt the message containing it?

I'm sure this has been asked before. Its just too blindingly obvious. from wikipedia "Digital signatures, in which a message is signed with the sender's private key and can be verified by anyone who ...
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TPM 2.0 Reissued EK Cert

Unlike the TPM 1.2 module, the TPM 2.0 specification allows the platform user to create own ...
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102 views

Does the public key and private key for WhatsApp only remain within a WhatsApp account

The world of cryptography is starting to really intrigue me admittedly. I initially hated it because it looked too hard Mathematically but now it looks cool :) Got a good question for the experts and ...