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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Encrypt and decrypt data accessible by two users on the web on multiple devices

I am currently building a website where a user will be able to upload a file to my server and another user will be able to download the file. Now i want to add encryption to this with the following ...
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How is asymmetric cryptography safe if one of the keys is public?

Let's suppose $A$ is sending a message $m$ to $B$ using asymmetric cryptography. To guarantee the authenticity of a message, $A$ encrypts $m$ with $A$'s private key: $E(m, k_A) = m_A$. Then, $A$ ...
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How to store private keys in browsers after Apple's decision to wipe script-writeable storage? [migrated]

We have a web application that puts a private key in LocalStorage, which enables users to sign off certain messages. It's been working fine until today we saw this announcement from Apple, https://...
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Possible Digital Signature Hack?

I am starting to learn more about cryptography and I just read more about how asymmetric keys can make a digital certificate, and I would like if someone could explain me why the following case can't ...
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Is there a digital equivalent to the Great Seal of the United States?

Since antiquity (and, for ceremonial purposes, up to the present day) physical document have had seals affixed to them. In principle, these seals allow anyone, if he knows what he's looking for, to ...
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Why is Multiplicative group used in RSA or Euler's theorem but not additive?

I am on the verge to understanding RSA, but suddenly a question popped into mind. When we are calculating $U(N)$ i.e $U(PQ)$, we are taking invertible elements that are co-prime to $N$. For example, $...
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How does WhatsApp retain private key? [migrated]

Does anyone know how does WhatsApp retain private key? Based on what I know it looks like private keys are stored on the device. What happens when someone changes their device? How does the private ...
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Research topics related to cryptography and Hamiltonian cycles

I am very interested in pursuing a research where I can show an application of Hamiltonian cycles in Cayley graphs of some group such as reflection groups to the field of cryptography. But currently ...
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How to find the inverse of a polynomial in NTRU-PKCS

I am coding a java based implementation of the NTRU public-key cryptosystem. I can comprehend the majority of the algorithms involved in the encryption and decryption process well enough, but the key ...
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is using secp256k1 curve for ECIES considered safe?

I read SafeCurves it indicates Secp256k1 is not SafeCurve by their standards but bitcoin and ETH use it in their blockchain. I researched more and figured out that using Secp256k1 ECDSA(singing ...
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data privacy, integrity and authenticity of distributed firmware images for an embedded device [closed]

Please assess the following suggested decryption and signature verification scheme. This is somewhat related to Types of Cryptography for a 4-8 bit microcontroller and similar to How to enforce data ...
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Combine signature with encryption

I have some embedded device for which I want to sign and encrypt firmware files. Firmware updates are generated by me and may be installed by the customer. The encryption is supposed to protect the ...
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Any ideas on login using Digital Signature PKCS

I am curious to know about possibility to login into web application just by identifying the user based on digital signature in usb token. any reference in this direction?
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Storing public key in cookie

I am encrypting my password before sending to my server with a public that i have stored as a cookie. Is there any security risks storing my public key in the cookie? Are there any better ...
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Classification of attacks against lattices

I'm interested about the cryptanalysis side of lattice-based cryptography, and was wondering whether there is a survey paper or something that gives some classification of attacks against lattices, ...
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Relationship between $N$ and $\phi(N)$ in the RSA algorithm

Recently I started learning how the RSA algorithm works and there is one single part of the computation which really confuses me and can't get over it. Let's say I chose 2 prime numbers, namely $P ...
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Are the signcryption and the authenticated encryption same?

The signcryption and the authenticated encryption are both the combine of encryption and authentication with three natural composition (i.e., EtS, StE, E&S). I am not sure that if they are the ...
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Is there a public key semantically secure cryptosystem for which one can prove in zero knowledge the equivalence of two plaintexts?

If Alice encrypts two messages $a$ and $b$, such that $x=E(a)$, $y=E(b)$. Can Alice prove (without revealing $a$, $b$ or the private key) that $a = b$? Obviously the proof must not be too long and it ...
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What's the main difference between Pohlig-Hellman and RSA?

Both Pohlig-Hellman and RSA perform encryption and decryption by exponentiation modulo some integer ($p$ prime for PH, $n$ composite for RSA). They both use a key $e$ as the exponent to encrypt a ...
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Applications of Group Ciphers

I've been reading a paper [1], and I've ran across something called a "Group Cipher", which is similar to homomorphic encryption, with an important difference. In homomorphic encryption we have an ...
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General Private/Public key generation [closed]

I wanted to get an idea on how the whole cold-storage private/public key generation works for different cryptocurrencies. So I was playing around with BIP32 deriviation path on: https://iancoleman.io/...
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Least knowledge ephemeral PKI?

I'm trying to build a PKI for document signing but only using 2nd party auth and no client persistence. I'm assuming I'd need to use something like a SCrypt key of the user credentials for the user'...
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Using SHA384 as an asymmetric cipher?

SHA384 is a hash function that can be (and is) used to verify data by checking it. Can it also be used as the background for a public-key crypto system? Here is what I mean: A 48-byte string is ...
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How big an RSA key is considered secure today?

I think 1024 bit RSA keys were considered secure ~5 years ago, but I assume that's not true anymore. Can 2048 or 4096 keys still be relied upon, or have we gained too much computing power in the ...
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Creating nested messages in OpenPGP

I need to create a nested message in OpenPGP (my understanding is that the protocol itself should support it). Let's say I have Payload ("Time in Lordran is ...
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Implementing symmetric encryption algorithms with whole words

Scenario I have some unique requirements to encrypt text: symmetric encryption; the encrypted text will be a valid text (that means that humans could read it and not just “gibberish”); I can not ...
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Is it secure to use ECDSA for any arbitrary point on the Elliptic Curve as the Generator point?

My question concerns the elliptic curve $E$ over a prime field $\mathbb F_p$. To the best of my understanding, ECDSA requires a Generator point $G$ of prime order $n$, and the $r$ and $s$ values of ...
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What is the use of a nonce in public-key encryption if it's meant to be shared?

I'm using PHP. The guys over at paragonie have made encryption easy for the PHP eco-system. Now, on my computer, Alice, when I ...
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Transition to post-quantum cryptography

Classical asymmetric cryptography is commonly based on the Discrete Logarithm Problem and Integer Factorization, which are known to be solvable with a quantum computer if it has the ability to run ...
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Why encrypt symmetric keys first with RSA and then the private-key with a PW?

In for example the Microsoft Encrypting File System, the SYM-Key is first encrypted with a RSA-Pub-key and its corresponding private-key is then encrypted using a users password. Why not encrypt the ...
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Fully Homomorphic cryptographic Scheme?

Given two FHE schemes FHE1 and FHE2 in which one of the two scheme is secure and other is not (we have no idea which is secure). Construct a FHE scheme which is secure using the given two scheme.
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Three Pass Protocol Question!

Alice and Bob have agreed to use the Three Pass Protocol. p=1009 Alice chooses the encryption exponent e_A = 101 Bob chooses the encryption exponent e_B = 209 Now Alice and Bob send three ...
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XTZ Private Key

The BIP39/44 off-line tool does not contain XTZ coin. Therefore, I cannot derive (from my 24 words) my ledger nano s private key associated with my Public key for my Tezos account. Is there another ...
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Are there any algorithms for which generating any zero-knowledge proofs is not practical?

It is related to my earlier question: Can zkSNARK or other zero-knowledge proofs be used to proof message authenticity without revealing private key? Are there any algorithms for which generating ...
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Secure multi-party computation for digital signature

Is there any practical algorithm that will allow to use public key cryptography (RSA or ECC) in the following way There are N parties. Up to M are malicious adversaries (were trusted, but got taken ...
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Can zkSNARK or other zero-knowledge proofs be used to proof message authenticity without revealing private key?

The situation: Alice and Bob are exchanging messages encrypted by some known asymmetric encryption protocol. All their encrypted messages, as well as public keys are intercepted by Charlie. Can ...
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Factorization problem

Say, $X= a\cdot b$, where $(a, b) \in Z_q^*$ and $q$ is a large prime. If $X$ is given, then what is the complexity (or hardness) of finding $a$ and $b$? Note that, either $a$ or $b$ can be reused to ...
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Why can't ransomware practically use RSA to encrypt all files?

I understand that a few ransomware have used an RSA public key to encrypt all files belonging to the victim. This is a bullet-proof system in terms of its security because the private key is always ...
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understanding LWE public key algorithm

I'm trying to understand this LWE public key system say I use matrix A = [[44, 73, 20, 54],[92, 19, 78, 22],[31, 34, 94, 29],[82, 32, 70, 68]] q = 97 bit = 1 and secret key s: [56, 90, 0, 46] and ...
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Advantages of encrypting a symmetric key with a public key vs using a fixed symmetric key

I am new to cryptography concepts. I am trying to protect some firmware download. Reading some Wikipedia pages, I understand that asymmetric cryptography is time consuming, so, if I want to protect ...
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Non-derivable public key asymmetrical encryption? [duplicate]

The need we have is to pass encrypted messages but such that the encryption key can't be generated from the decryption key. This sounds like with vanilla asymmetrical crypto I know, but in every ...
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Same ephemeral key for 2 uses

I am theorising an onion routing network, and I have a question about ephemeral keys. This is the basics e2e connection encryption protocol. ...
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Multiple sender single receiver Encryption

I had this article given to me by my teacher, and I would like to enhance it. It's titled Modified El Gamal Algorithm for Multiple Senders and Single Receiver Encryption. I planned on having the ...
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Forward Security of Symmetric Encryption Schemes with LFSR based PRNG

Forward security can be achieved using symmetric encryption schemes by combining with a pseudo-random number generator (PRNG). Does LFSR based PRNG provide forward security in this case?
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How are precision and security related in a Gaussian Noise Sampler for R-LWE?

My understanding is that the sampling precision in Gaussian Noise sampler is related to security. But not sure about why is that? I read that when the samples are floating-point numbers and precision ...
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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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Is 128-bit security still considered strong in 2020, within the context of both ECC Asym & Sym ciphers

Given that much of our ECC crypto primitives provide “only” 128-bit security when defined over a 256-bit curve due to pollard-rho, is it then still safe in 2020 to consider 128-bit security safe for ...
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Diffie-Hellman Key Exchange with Authentication: Man-in-the-Middle query

I have been reading up on MiTM attacks, and the prevention of them using public key certificates. Recently I learnt about Diffie-Hellman Key Exchange with Authentication, and how it uses signed ...
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Derived keys usable by threshold signatures

Suppose there are $n$ members in a $(t,n)$ threshold signature scheme. The global secret key $sk$ is not known to any single party, as the keys are generated distributed. The parties are able to ...
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Help with cryptanalysis of branching in schemes based on Multivariate Public Key Cryptography

I'm familiarized with the structure of branching found in Multivariate Cryptography, as it allows us to partition a $n$-tuple over $F_{q}$ into a $k$-tuple where the $i$-th element is in $F_{q^{\...

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