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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Do there exist cryptographic algorithm where secret key holder can distinguish ciphertext corresponding to without decrypting?

I am looking for some cryptographic algorithms suit to the below usage scenario. $A$ has a set of data, e.g., $\{x_1,x_2,...,x_n\}$. $A$ publish those data in ciphertext (maybe that they are encrypted ...
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What is the most secure hybrid cipher suite(Library) possible today?

What combination of public key cryptography (DH) and symmetric key cryptography is currently available that is (subjectively) as secure as possible over other ciphers (AES,curve448) when security is ...
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ECDSA SECP256k1 curve - same-r-value-is-used-for-two-different-addresses

Edited: changing the notation according request by fgrieu. I have prepared 4 transactions for 2 pubkeys with the same r1 and r2. properties of secp256k1: ...
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Iteration count for (enhanced) Miller-Rabin

In FIPS 186-5 (Digital Signature Standard or DSS) there is a Table B.1 which specifies the minimum number of rounds of Miller-Rabin testing for 1024, 1536 and 2048 bit keys, used for digital ...
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is this how RS256 works in JWT?

I'm a newbie that is studying about JWT using RS256 algorithm for signing and verification. I have drawn a diagram that represents my understanding of how RS256 works. Basically, below is what I ...
William Le's user avatar
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Question about Security of Multi-Signature Scheme

I am a developer trying to follow best practice guidance as established by the IETF for my applications. I was researching standards for ECDSA key generation for some work that I have to do in the ...
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Solving DDH from an ElGamal adversary

Suppose an adversary wins IND-CPA against ElGamal, They're given public key $h=g^x$, Give a pair of messages $m = [m0,m1]$, Get back ciphertext $(a,b) = (g^r, g^{xr} \cdot g^{m[b]})$, from which ...
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Is there a name for an encryption scheme that do not return $\bot$ when a different key is used during decryption?

Given an encryption scheme $\Pi = (G,E,D)$, either public or private, is there a name or a property to emphasize that for $c\gets \Pi.E(k,m)$, where $k$ is a key and $m$ is a message, we want $m^\...
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How to map point from one EC to another EC?

p = 115792089237316195423570985008687907853269984665640564039457584007908834671663 How to map points from curve ...
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How to calculate points for twist?

How I can find the point to perform this twist attack - https://cryptodeep.ru/twist-attack/ English version of previous link: https://github.com/demining/Twist-Attack This video has additional ...
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How can we reverse Elliptic Curves after solving the DLP problem?

Suppose that I've solved the Discrete Logarithm problem. Can someone explain to me in terms of the example below how to arrange values of Elliptic Curve secp256k1 in a reverse form so that I can ...
UnpluggedTrio's user avatar
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Decentralized identity, how to prevent duplicate uses of the same identity

In a system that relies on decentralized identity, is it possible to prevent duplicate uses of the same real-life identity, i.e. same real-life person creates more than one user entity (each is ...
rapt's user avatar
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Publishing a message with a computationally enforced delay [duplicate]

I'm looking for a way to publish a message, so that it will only be publicly known after some time (let's say a few minutes). Even I shouldn't have the power to prove what my message was, before this ...
Filip Sondej's user avatar
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How to decrypt c when e is not co-prime with phi(n) and e is non-prime

In RSA, I want to know a way to be able to retrieve all possible plaintexts $m$ given a ciphertext $c$, $\phi(n)$, $n$ and $e$. The decryption exponent $d$ can not be generated due to the fact that $e$...
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KEM security definition - IND-CCA vs IND-CCA2

When researching about PQ KEM's I have come across two different definitions of indistinguishability under (adaptive) chosen ciphertext attack. IND-CCA (https://eprint.iacr.org/2017/604.pdf page 10, ...
honzaik's user avatar
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Construction of a SKE scheme based on a PRF family and on a MAC with UF-CMA security. Is the scheme secure?

Consider the following construction of a SKE scheme $\Pi^*=(Enc^*,Dec^*)$ based on a PRF family $F=\{F_k:\{0,1\}^n\rightarrow \{0,1\}^n\}_{k\in\{0,1\}^\lambda}$ and on a MAC $ Tag:\{0,1\}^\lambda \...
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Public-key authentication that is feasible by hand, before computers?

I wonder if it's possible to do public key authentication (preferably not vulnerable to replay attacks) before modern computers became a thing (e.g. in a medieval setting). Specifically: ...
Azuresonance's user avatar
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RSA public keys such that encryption is identity

In this question, we restrict to RSA public keys $(n,e)$ such that $n$ and $e$ are odd, $3\le e<e_\max$, $e<n$ Note: For some old Windows API, $e_\max=2^{32}$. In FIPS 186-4, $e_\max=2^{256}$. ...
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Can you restore a private key from biometrics?

My understanding is that iOS FaceID/Fingerprint for example use an underlying mathematical representation of the biometric features. Is it possible to generate a key pair from this representation and ...
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UF-naCMA not implies UF-CMA

I am trying to show that UF-naCMA doesn't imply UF-CMA. UF-naCMA is actually defined as UF-CMA but the adversary should send $q \in poly$ messages $m_i$ chosen non-adaptively (i.e. all at the same ...
Cristie's user avatar
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Generating public/private key pair from data and shared password

Two parties share a password. They need to now exchange some data. Is there a way where one party generates a public/private key pair from the data and password and shares just the public key with the ...
sandeep kiran p's user avatar
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They key size of the Schnorr Signature Algorithm

Based on the Schnorr signature below: What is the suitable size of lamda to generate a secure key?
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Is RSA longer supported in TLS 1.3 and are RSA and DH fundamentally different?

I'm watching "SSL, TLS, HTTPS Explained" by ByteByteGo on YouTube and at the end, starting around 5:15, there are two points that are interesting: in TLS 1.3 RSA is no longer supported as ...
c_idle's user avatar
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NTRUEncrypt fails on sedonion algebra

This question is a direct follow-up (hopefully - the last) of my previous one; please see it for full information. I would like to further generalise NTRU cryptosystem on higher-order algebras. ...
max's user avatar
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Troubleshooting ECDSA implementation in rust [closed]

I'm trying to implement ECDSA for learning purposes and have generated public and private keys, which seem to be correct as I have compared them with those generated by an online tool called noble. ...
Question's user avatar
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NTRUEncrypt fails on quaternion algebra

This is a follow-up of my previous two questions (1 and 2), might be relevant to check them out first for a full context. I am trying to re-create results from this paper. The basic algorithm is ...
max's user avatar
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Is exposing hash of private key provably secure?

Let's say we have an IND-CPA secure public key encryption scheme $\Pi = (\text{Gen}, \text{Enc}, \text{Dec})$. Construct a new PKE $\Pi' = (\text{Gen}', \text{Enc}', \text{Dec}')$ that behaves exactly ...
puppet puppet's user avatar
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Convert a Schnorr Public Key to a compressed ECDSA Public Key

Given a Schnorr Public Key (32 bytes) x, I'd like to generate a compressed ECDSA Public Key (33 bytes) and thus be able to generate the bitcoin address that the private key holder can generate with ...
FreeTrade's user avatar
2 votes
2 answers
420 views

Why is it impossible for asymetric ciphers to be stream ciphers?

My studying material states that although symmetric ciphers can be either block or stream ciphers, it also states that asymmetric can only be block ciphers without further clarification.
BenTucker's user avatar
3 votes
1 answer
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Zero knowledge proofs that one has broken a crypto system

Suppose someone has figured out how to factor integers in polynomial time, thus breaking the RSA system. Also suppose this person does not want to reveal the secret of how to factor integers in ...
Craig Feinstein's user avatar
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1 answer
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Encrypting messages with two different public keys

The problem I have is next: There's the centralized DataBase app which has its own private key and sends its public key to its customers. Each customer has its own private key and should be able to ...
Dusan Markovic's user avatar
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X509 Client certificate - before - XEnroll / Certenroll / KEYGEN

IBM (now HCL) Domino has since way back a complete procedure to issue X509 client certificate as a login option to a webserver. Back in 2010-ish it worked fine in both Firefox and Internet Explorer. ...
Stefan K's user avatar
3 votes
1 answer
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Proof-of-Randomness with an EC Public Key

I will be using a tRNG to generate EC keypairs on a Secure Integrated Controller. I need to demonstrate I, the issuer, can not know the private key without colluding with the user to obtain it, even ...
WindowCleaner's user avatar
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1 answer
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Public key fingerprint verification for large groups

If you were designing: An open source client that offered E2E encryption for e.g. folder sharing between users Each user had public keys for signing (and separate public keys for encryption of ...
gecad41980's user avatar
3 votes
1 answer
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Max message length when encrypting with public key

The question is what is an appropriate public/private key length in order to encrypt a 256-bit or 512-bit AES key without wasting bytes, and whether long public/private keys provide meaningful ...
Per's user avatar
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2 votes
1 answer
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Self-contained digital certification device

Does it work if we try to construct a device (e.g., for counting purpose in several remote branches of a company) using a self-containing digital signature key enclosed in a tamper-proof hardware to ...
oCriptoPanquer's user avatar
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1 answer
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Is considered safe saving encrypting files using asymmetric encryption algorithm inside public environments?

I know restricting access of a file, is a important measure of security. If we read the Payment Card Industry's Data Security Standard (aka PCI-DSS), we can see a requirement where control access must ...
Carl_Dude's user avatar
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CPU cost of signing vs. encrypting

I'm protecting communication between some microservices using public/private key encryption, where the sending container has a public key and the receiving container has a private key. This both ...
Per's user avatar
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2 answers
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IND-CPA secure PKE from search problem

Is there any PKE scheme that is IND-CPA secure (in a standard model, not RO) under a search problem?
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1 answer
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NTRUEncrypt fails on complex algebra

I am following the NTRUEncrypt cryptosystem as described on the wikipedia. I have implemented it in Sage Math engine (with small problems along the way, but in the end - succesfully resolved) and the ...
max's user avatar
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2 votes
2 answers
136 views

Why does NTRUEncrypt fail on different values for large modulus?

I am trying to closely follow the algorithm here (keeping the same variable names) and reconstruct the cryptosystem in Sage Math engine. It seems to work on parameters ...
max's user avatar
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1 vote
1 answer
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Digital Signature and Encryption Process / Hierarchy

I'm trying to get my head around this scenario. I understand that a private key can be used for signing a message to provide authentication and public key can be used for encrypting and its ...
Yusuf Ning's user avatar
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Can you use MITM to hijack a public key meant for key based signing?

After reading "Verify the identity of sender" , which was part of an answer on StackOverflow, I was wondering if the following is possible: Based on part II, if I am sitting between Alice ...
Tom's user avatar
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1 answer
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Signature operation of RSASSA-PKCS1-v1_5 requires private key. Superficial limitation, or are public parameters mathematically incapable of it?

In the case of RSASSA-PKCS1-v1_5, is it simply that the cryptographic libraries and APIs are designed to only sign if determined superficially that it has a private key, or is the public key ...
fartwhif's user avatar
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Blom's key distribution

Having a difficult time wrapping my head around the Blom's key distribution. I found an online resource to understand this but still couldn't get it. I am attaching the screenshot from the book where ...
jammy's user avatar
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Are Digital signatures used enough these days?

So I'm currently working on a past exam paper related to cryptography, this question essentially asks the reader why digital signature schemes are not used today. Yet, when I did my research on this ...
Thanos's user avatar
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1 answer
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How to achieve encryption at single source and decryption at multiple locations using asymmetric scheme?

I need an encryption scheme where a single source/location can encrypt using their private key and while anyone with access to the corresponding public key can decrypt it. It has to be asymmetric to ...
Rahul Parthe's user avatar
2 votes
1 answer
322 views

Why can't RSA signatures be forged algebraically?

Compute $n = pq$ where p and q are prime. Fix $e$ to be coprime to $\phi(n)$. Compute $d = e^{-1} \pmod n$ and verify $ed \equiv \phi(n) \pmod n$. We sign the (hash of) a message with $s = h^{d}$. A ...
Jeffrey's user avatar
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What is a website's private signing key used to sign?

I am trying to understand digital signatures and digital certificates. I know that digital certificates verify a server's public verification key but what does the website's (client) private ...
CryptoGuru's user avatar
1 vote
1 answer
210 views

End-to-end mobile chat application

I'm creating a mobile chat application using python (django) as backend, and I'd like to implement an end-to-end (E2E) cryptographic system for protecting messages. Now, as I understood so far, when ...
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