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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Public-Key Encryption with Privilege Access: is it possible?

Let be Alice, Bob, and David three people. They all have public-key cryptographic system: private key and public key. Is there any way, in some known cryptographic system (RSA, Elliptic Curve, etc.), ...
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Public key stored in PKI [closed]

In a public key infrastructure how does a User A communicate with the user B? How does user A send his public key to user B ? Where is a public key stored where do they retrieve it from? This question ...
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It is possible to prove that two private keys are related?

Say Alice owns two keypairs: ($Pub_1$, $Priv_1$) and ($Pub_2$, $Priv_2$). The pair ($Pub_1$, $Priv_1$) is pretty mundane. $Priv_2$ was intentionally created by Alice by concatenating $Priv_1$ and the ...
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Which solution is the more protected?

I am wondering which of these two solutions is better for security on the long run. The problem is: Alice and Bob exchange a secret key/private key. Then they go far away from each other and never ...
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Menzes-Vanstone variant for Elliptic Curve Cryptography ElGamal in SageMath

I'm using Sage for a cryptography class and I have to implement the Menzes-Vanstone variant for Elliptic Curve Cryptography ElGamal, which is described here. In the last line there is a type and ...
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How can I dentify the ECDHE group value used in a TLS session

In ECDHE, the group is a public value. I want to get this value for a session. I inspected the session using Wireshark. Under the ServerHello -> Key share extension -> Key share entry, I found ...
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Randomness space of encryption function

I was reading the definition of Fujisaki-Okamoto transform, and I found this: What does it mean the "randomness space" of the function Enc in the PKE setting?
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OpenSSL: How to convert ec private key(32byte raw key) to pem type private key?

I have a 32 byte octet string ec private key. And I want to convert this to pem type private key. I use the secp256r1 curve. How can I do that? Is any command or method for that?
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Is this RSA cryptosystem safe? [duplicate]

Suppose Bob uses the RSA cryptosystem with a very large modulus $n$ for which the factorization cannot be found in a reasonable amount of time. Suppose Alice sends an enciphered message to Bob ...
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How do you get a Public Key from a Fingerprint

I've seen some people putting their public key's (I'd suppose they refer to a PGP PK) fingerprint on powerpoints and alike so that they can be reached out to using a safe channel. From my POV, it's ...
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Does sha256 is ok for that? If not does EC?

I think from what I studied that I had the correct reasoning, but I would like a double check. Here is the thing: Given two matrix: A and B I calculate the hashFunction(A, B) = C Now I calcultate the ...
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Generate asymmetric key pairs based on keywords such that any public key based on set containing the generating subset is valid

Let's assume we have a ton of users, and each user has a list of fruits they like - Those will be keywords. I want my users to be able to encode any data they store (Let's say, the location of their ...
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How to exchange a credential whilst ensuring deniable authentification?

This is a follow-up to this answer. The context & vocabulary used is that of a decentralized identity system. Let $I$ be the issuer of a credential, $H$ the holder and $V$ the verifier. In this ...
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Protect messages in online messaging system

On a website, I would like to implement a system where users can message each other. The content of the messages should be protected against attackers that are trying to read them. My first thought ...
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Clarification on hybrid encryption vs ECIES vs symmetric encrypt the message and then use assymetric for key

I am trying to understand Hybrid encryption. When I first came across the term I though it is used to describe a scheme where the message is encrypted using a symmetric key, and the symmetric key is ...
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Good asymmetric algorithm for Java keytool as of 2021

While I expect to get flak for the term "best", some algorithms are widely considered better than others for essentially all purposes. For example, DES is no longer considered secure. My ...
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Prove CPA security [closed]

Assume $(Gen, Enc, Dec)$ is a public-key encryption scheme with message space M that is CPA-secure. Prove that the encryption scheme $(Gen^2, Enc^2, Dec^2)$ is CPA-secure. $Gen^2=(pk_0, sk_0) \...
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Why can't we use the Zeta function to search for prime factors in RSA?

Maybe I got this wrong, but if the Zeta function is efficient to compute and reverse, and if Riemann's assumption is true (which it seems like), can't we use the Zeta function to efficiently find ...
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Cheapest way to prove that two different private keys are known to the same person?

Say that there are two unrelated ECC keypairs ($Pub_1$, $Priv_1$) and ($Pub_2$, $Priv_2$). Alice claims that she knows both $Priv_1$ and $Priv_2$, but Bob doesn't trust her, and thinks that $Priv_2$ ...
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Incompatible key types

Consider the following. I have a decentralized network of nodes that can talk to each other, and I'd like to encrypt their communications. I turn to asymmetric encryption, the way most of the ...
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Is it possible to calculate multiplication inverse of a point on elliptic curve?

The title must be confusing. Imagine we have this curve: $y^2 = x^3 + 9x + 17$ over $\mathbb F_{23}$ And we know [4]P = (19 , 20) [8]P = (12 , 17) If we only have the value of $[8]P$, Is it ...
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How does SSH generate keys for RSA algorithm?

As far as I understood, the core of the RSA algorithm is to have 2 (large) primes ‘p’ and ‘q’, so that ‘n=pq’. Then ‘n’ is the public key, and ‘p’ the private one. The security comes from the fact ...
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Asymmetrically encrypt a short message into a short string

I have a string whose size is < 32 characters from the following limited character set. uppercase and lowercase Latin letters: A to Z and a to z digits: ...
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Cracking secret key, n, and m by hand with the Diffie-Hellman key exchange brute force

Problem: You see Michael and Nikita agree on a secret key using the Diffie-Hellman key exchange. Michael and Nikita choose $p = 97$ and $g = 5$. Nikita chooses a random number n and tells Michael that ...
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Is encrypting every number separately using RSA secure?

Suppose RSA is considered a "secure" method for encryption. RSA is meant to encode a sequence of integers base $27$. If we use an $n=pq$ that is hard to factor, Is it still secure if we ...
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Building an adversary for a OW-CCA game

Let K_rsa be a RSA genertor with associated security parameter k >= 1024. Let game OW-CCA_Krsa be as follows: How can I build a O(k^3)-time adversary A making at most 2 queries to Invert and ...
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Current status of ring signatures/proof of set membership

I understand the original O(n) implementation of a ring signature, but I'm trying to figure out where the state of the art is on signing a message as an anonymous member of an ad hoc group without ...
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Decrypt AES-128-CBC encypted partial RSA Key

I am given a private RSA key, which header indicates that it is AES-128-CBC encypted. Note that the last ten lines of the key are missing. (This is part of an educational task.) ...
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Is it possible to have a shared secret without any party knowing all the parts?

I believe with Shamir’s Secret Sharing Scheme, I can create an n-part secret and distribute each of those parts to n parties. ...
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Timing attacks: Symmetric vs Asymmetric Algorithms

There is a statement that I can't give a reference; "Since the timing characteristics of symmetric algorithms are not as key dependent as asymmetric algorithms, they are more resistant against ...
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Why are public keys derived from elliptic curve cryptography (ECC) and not from hashing?

I've just started studying Bitcoin and cryptocurrencies, so I might be wrong, but so far my understanding is that public keys are derived from private keys using ECDSA, in Bitcoin's case using ...
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Proof that exchanged variable was not modified with MITM

If I understand correctly, the core of man in the middle attack is in being able to replace an exchanged variable (public key) with another. Hence to detect a MITM one needs to check if the exchanged ...
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How secure is it to use a 128-bit random seed to derive a 256-bit key for seeding key-pair generation?

We are developing an open-source peer-to-peer app, Mapeo, designed for users with low technical experience (and no email or phone) to collect data in offline environments. We are generating their ...
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Would being able of factoring integers efficiently have some consequences over Elliptic Curve Cryptography?

Let's assume you can factor integers in a very efficient manner. Would that endanger the security of e.g. elliptic curve cryptography, or is there no link between the two ? You can often read that ...
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Is qTesla Secure?

qTesla is a signature scheme and a submission to the NIST post-quantum standardization process, which made it to the second round. It is based on the hardness of RLWE. The NIST round 2 status report ...
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How to convert plaintext to element of cyclic group in Cramer-Shoup cryptosystem

I am trying to implement a cramer-shoup cryptosystem but I don't understand how to work with the plaintext I want to encrypt. From what I understand, the plaintext needs to be converted to an element ...
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ZKP: Prove that >18 while hiding age

I am relatively new to cryptography, but I've been programming for a while. Here's a story that sets well the problem I'm trying to solve: Alice has a digital passport that's signed with her ...
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Modes of operation for public key encryption [duplicate]

Why do we not define modes of operation for public-key encryption just like how they are defined for block ciphers?
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Is asymmetric decryption guessable?

I am not an amateur in cryptography so this might be a very basic question. I am interested to know if there exist ciphers such that if I encrypt a message with it and then lose first say 300 bits ...
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What are the misconceptions of IBM's CEO Arvind Krishna talk on the "Axios on HBO" about the quantum computing

IBM CEO Arvind made a talk in HBO's Axios program. It seems that there are misconceptions/misleading/flaws in reasoning etc. What are those! Some of the details of the speech is given as; IBM says ...
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What is reaction attack?

In the paper of "Reaction Attacks against Several Public-Key Cryptosystems" CiteSeerX link, reaction attack is defined informally as "Obtaining information about the private key or ...
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Encrypted data sharing in decentralised system

Alice encrypts file using her public key and upload it to decentralised file store (some service). Bob buys access to the file. Is it possible to share decrypted file with Bob without having Alice's ...
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What is/was SEC#1 ECC public key leading octet 0x01 for?

In the SEC#1 elliptic curve cryptography standard, the encoding of the public key involve a leading octet: 00h: The public key is the point at infinity. 02h, 03h: The public key is the compressed ...
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How to ensure the data comes from verified source without using asymetric encryption

I'm building a project that is remotely controlled using LoRa and I want to ensure, that nobody can imitate my transmitter and send packets to my receiver. Just encrypting sent data is not enough ...
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Question about white-box rsa algorithm

I found a scheme for white-box RSA. It seems to protect the input and output of modular operations. I'm curious about how to analyze the security of this solution. Does anybody know anything about it?
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Why is confusion and diffusion never talked about in asymmetric crypto?

While talking about symmetric encryption schemes like AES we always have a goal of achieving confusion and diffusion. But when it comes to asymmetric encryption schemes like RSA, DH etc. we never talk ...
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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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Is Diffie-Hellman Key Exchange an Asymmetric or Symmetric Algorithm? [duplicate]

To my understanding, the DHKE algorithm is symmetric since it only produces a shared secret, rather than public and private keys, however googling "is diffie hellman asymmetric?" results in ...
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Why does Shamir's Trick for RSA Work

I have read that Shamir's trick can protect RSA with CRT against fault attacks. However, it is not clear to me why the following equations $$ s_{p}^{*}=m^{d \bmod \varphi(p \cdot t)} \bmod p \cdot t \\...
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Multiuser encryption, singleuser decryption [duplicate]

I have an hybrid encryption (RSA, AES) for a file sharing project I am working on, where I use a single public key for encryption on the sender side and corresponding private key for decryption on the ...

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