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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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2answers
84 views

RSA exercises example

I have doubts about this question Consider the following textbook RSA example. Let be p = 7, q = 11 and e = 3. Give a general algorithm for calculating d and run such algorithm with the above ...
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1answer
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Database and End-to-End Encryption

I'm currently designing a mobile/desktop application to synchronize some messages or notes. I'm searching for a way to secure it and to avoid letting the server be able to read the messages. My goal ...
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Diffie-Hellman key exchange in four parties [on hold]

I understand the concept of 2 and 3 parties Here is the code of 3 parties ...
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0answers
21 views

How do I go about managing keys? [on hold]

I need a way to send a message and need a way to guarantee integrity and authenticity. I want to use HMAC but how do I go about using the public/private keys? And how do I get them?
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4answers
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Why use symmetric encryption with Public Key?

A. From what I heard (and I am beginner at a security/cryptography), if you have a payload that is very large, asymmetric is a no-go. B. Also, if you do have secret symmetric (e.g. AES) keys, you ...
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What is the current state of the Conjugacy Search Problem in Matrix and Permutation Groups?

It results that I have come with a mathematical approach to solve the CSP (Conjugacy Search Problem) where the platform group $G$ is either a permutation group or a Matrix Group. From my part I ...
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1answer
7k views

Can an RSA private key have several public keys?

Ok, so my cryptography lecturer in University posed this question at the end of the RSA key generation lecture as a brain teaser. I have been thinking about this and I think I have come up with a way ...
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Why is it important that phi(n) is kept a secret, in RSA?

Why is it important that $\phi(n)$ is kept a secret, in RSA?
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131 views

Corporate PKI - SHA1 deprecation [closed]

Here is the context. Suppose you have a corporate PKI with : AC_Root (offline in safe store - SHA1 signature) SubRootA ans SubrootB (offline in safe store - SHA1 signature) SubSubRootC, SubSubRootD, ...
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1answer
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I am new to digital certificate 509V3 concept. can some one please clarify the below points [closed]

I am using RSA 2048 with SHA 256 primitive in certificate: How to verify the user certificate n + 1 with Root certificate n? why it is required to perform Certificate chain verification? How to ...
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1answer
316 views

PKCS1 v 1.5 Signature questions

I'm crash studying the public key cryptography topic and I have a few questions about how signatures are created. So are digital signatures just encrypted hashes? If that's the case then I can hash ...
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2answers
185 views

Digital signatures with one-way function, can messages be longer than the signature?

Ethereum and Bitcoin both use 512 bit signatures, can the message that is being signed be longer than 512 bit?
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1answer
983 views

How is public key cryptography used for digital signature?

In public key cryptography, there are two different keys used for the encryption and decryption of data . I am wondering how it is used for digital signature
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1answer
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How can one validate with a public key a JWT signature generated with a private key?

As I understand it, a JSON Web Token (JWT) consists of 3 parts: the header, specifying the hashing algorithm to use for the signature; the payload itself; and the signature, which is a hash of the ...
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1answer
79 views

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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1answer
36 views

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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1answer
419 views

RSA-OAEP Padding scheme

Honestly I'm really confused about padding in RSA scheme. I don't study computer science, and I'm a beginner learning cryptography (self-taught). Can anyone give me suggestions?
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1answer
63 views

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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1answer
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Is there another group structure that is suitable for RSA other than $U_{pq}$?

I know that calculating the cardinality of $U_{pq}$ is infeasible and therefore it is extremely hard to break a code using Lagrange's theorem. But later on my studies i realized main principle of RSA ...
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1answer
112 views

Chosen Plaintext Attack and Chosen Multiple-Plaintext Attack

The original CPA game: The adversary gives two arbitrary messages $m_0$ and $m_1$ to a challenger; The challenger encrypts an arbitrary message $m_u$, $u∈\{0,1\}$ , and sends the ciphertext to the ...
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2answers
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How does this formula work $(aG + bG) = (a + b) G$ in ECDSA?

Please explain how does this formula $(aG + bG) = (a + b) G$ work in ECDSA? According to the source: $a$ and $b$ are different private keys Suppose $a = 3$ $b = 4$ then the public key is $Q = aG$...
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1answer
54 views

What's the proper way of fitting hash digest to encryption scheme?

I would like to know what is the proper way of fitting the hash digest to the prime in which the encryption scheme operates. regardless if the bits of the hash digest is larger or smaller than the ...
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1answer
31 views

Is it possible to execute elliptic curve encryption on small sensor-tags CC2650?

I am working on a project wherein ECC needs to be implemented on small devices, namely, CC2650 sensor-tags for authentication. The ECC implementation should be on Contiki OS. I have read some articles ...
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1answer
210 views

Is there a feasible way to generate an RSA key manually the same way as it is for an ECC one?

In elliptic curves, a private key is just a random number, and one relatively small compared to other crypto systems (256 bits for ECC vs 4096 bits for RSA for example). Suppose I don't trust ...
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1answer
35 views

Securely derive AES and ED25519 keys from a ED25519 seed

Go's ed25519 package exposes a function which allows creating a private key from a 32 byte seed. See: https://godoc.org/golang.org/x/crypto/ed25519#NewKeyFromSeed The reason I want to use this is ...
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1answer
48 views

Is it possible to construct dataset for only another party to consult?

Is it possible to construct a dataset made of some kind of probabilistic encrypted indexes such that anyone can update the information contained in the set but only the one with a secret key could be ...
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1answer
96 views

Paillier Private $\mu$ and $\lambda$

The Paillier CryptoSystem has a public key that $(g,n)$ and the private key which can be exclusive to $\lambda$, where the decryption scheme is: $m = L(c^\lambda \bmod n^2)/L(g^\lambda \bmod n^2) \...
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1answer
206 views

What happens when i sign a public key with its private key pair?

I am not a cryptologist, just a cryptography user, so not sure if this is safe. I want to sign a public key with its private key pair. Is it dangerous to share this signature result along with ...
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Authenticating Public Keys Recieved On Blockchain PKI

I am trying to understand how a PKI could be stored on a blockchain so as to eliminate the need for centralised CAs. How does every node on the network who receives a new block containing an ...
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1answer
125 views

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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RSA factorization [closed]

I'm trying to factor the given modulus, to find $p$ and $q$ so I can calculate the totient and then use that to decipher a message, but so far most of my attempts have fallen flat. I did notice that ...
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3answers
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Why are asymmetric cryptography keys more vulnerable to brute force attack than symmetric ones?

I came across this paper which says that Asymmetric keys must be many times longer than keys in secret-cryptography in order to boast equivalent security. Keys in asymmetric cryptography are ...
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1answer
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RSA figuring out the recipient of a ciphertext

I have this question I am trying to figure out the answer about RSA. I'd be grateful if someone could actually help me understand how the procedure would work. I am new to cryptography and with all ...
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0answers
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What are some examples of out of bound channels that work over the Internet in practice?

If I want to verify a public key (be it RSA, PGP, etc.) with another client over the Internet only, what are some viable out-of-bound channels for verification? Which channels have been used in ...
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1answer
72 views

Hashing using asymmetric cryptography

Every now and then, we read that some hashing function has been weakened or broken, but we almost never hear this for asymmetric cryptosystems like RSA or ECC. That's because while asymmetric ...
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1answer
52 views

Is it possible to calculate the random factor $r$ from a encrypted message and the private key in a Paillier cryptosystem?

I have already done my research and found various sources that state that it is possible but there are also a lot of them that says it is not possible to recover $r$. This Q/A on this site for example ...
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1answer
33 views

What happens after sharing the secret key in quantum cryptographic schemes to send the message bits?

As a person working on the physics perspective of quantum communication, I understand the process upto which the quantum key is shared securely. What happens after this process to send message bits? ...
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Resetting a shared private key

I have a scenario with a user that needs to operate on common data from multiple devices but the link to the server is often offline. Unfortunately in the environment, I trust anything not directly in ...
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0answers
54 views

Recursive RSA encryption

I have a ciphertext $C$ encrypted with public key $pub_C$, which contains ciphertext $B$ and $pub_B$, $$C= E_{pub_C}(B\mathbin\|pub_B)$$ Ciphertext $B$ is encrypted with $pub_B$ and contains $pub_A$ ...
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34 views

Zero-knowledge commitment verification

Assume everything takes place in a prime field. Given the following: $g$ - generator $s$ - secret $E(K, m)$ - a public-key encryption function using public key $K$ and plaintext $m$ The ...
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4answers
3k views

Why should the RSA private exponent have the same size as the modulus?

Consider the generation of an RSA key pair with a given modulus size $n$ and a known, small public exponent $e$ (typically $e = 3$ or $e = 65537$). A common method is to generate two random primes ...
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1answer
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Deterministic procedure for mapping an arbitrary value into a 𝑝,𝑞 pair for public key cryptography

I want public key cryptosystem to used for re-encryption as describe in Can Paillier ,RSA or any other schemes be used for universal re-encryption like elGamal? Now i have little solution for ...
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0answers
5 views

get bitcoin cash address from public key, using bitcoin-abc [migrated]

hey i am using https://github.com/Bitcoin-ABC/bitcoin-abc and trying to get bch adress form ecdsa public key. I have this compressed public key: ...
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1answer
87 views

Determine the RSA private key from public key

I was told that you can determine the private key of an RSA encryption with the public key. I thought the point of a public key was to avoid letting people find the private key, but anyway, they said ...
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0answers
30 views

End to end encrypted web chat app with stored messages in database

I am working on a web app with an integrated chat. All chats can only occur between two users - not more, not less. I am very concerned with security, so I would like to encrypt all chat messages with ...
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3answers
8k views

What is Identity-Based Encryption (IBE) and why is it “better”?

Most CS/Math undergrads run into the well-known RSA cryptosystem at some point. But about 10 years ago Boneh and Franklin introduced a practical Identity-Based Encryption system (IBE) that has ...
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2answers
16k views

Where and how to store private keys in web applications for private messaging with web browsers

I am working on a web application enabling users to communicate over private messages which is just one part of the whole system. The main focus during my development process is to protect the privacy ...
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1answer
2k views

Multi-key decryption

Let's assume I want to send a secret message to $N$ recipients in an asymmetric way. My message could be encrypted with $N$ different public keys $p_i$ one after another and send to each user ...
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1answer
70 views

Probabilistic verification of signature schemes like RSA?

I was wondering if there were any verification algorithm in the literature that enables a "probabilistic" verification of well-known signature schemes? For RSA signature verification for example, is ...
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0answers
54 views

Homomorphic Public/Private Key Encryption Scheme for Floating Numbers

Is there any public/private homomorphic encryption scheme that directly works on floating numbers or vectors of floating numbers? In our application, we want to find out if $$v_1 \approx v_2, \qquad\...