Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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 ...

4
votes
1answer
617 views

Understanding WannaCrypt's hybrid encryption scheme

I'm confused about how WannaCrypt's hybrid encryption scheme works after watching Computerphile's "How WannaCrypt Encrypt's Your Files" video a number times. Below is my thought process to make it ...
0
votes
0answers
49 views

Lattice Reduction Method to solve multivariate equation

I have seen very small work in multivariate RSA polynomial modular equation solutions using Coppersmith's based lattice reduction algorithm (LLL). Is there any mechanism to solve the following type ...
1
vote
0answers
57 views

Using NewHope key exchange between browser and BouncyCastle implementation

I have been looking around with some new Post-Quantum secure key exchange methods, such as McEliece, NTRU and SIDH, but none of these seem to be working nicely between the browser and the BouncyCastle ...
2
votes
1answer
82 views

DSA signature computation

Reading through the DSA signature specification, one thing stood out for me. $r = (g^k \bmod{p} ) \bmod{q}$ Then $s$ is computed. In the computation above, why is the modulo $p$ required, given we ...
0
votes
0answers
32 views

Authorizing someone to open Alice's lock when Alice's lock only has Alice's public key

I'm designing a lock and I want Alice to be able to give temporary permission to someone to open the lock. After a set amount of 'access time' that someone should not have access to open the lock ...
2
votes
2answers
145 views

Broadcast encryption not using symmetric keys

Is there a common scheme for a broadcast style encryption that doesn't involve and exchange of a common key? I'm aware that traditionally what would be done is there would be a common symmetrical key ...
0
votes
0answers
28 views

Long term Public keys Vs Long term Secret key (LTPK vs LTSK) [duplicate]

I am new to cryptography and I was curious what is the difference between long term public key and the long term secret key. How are they used in the security process? What is the scope of the keys ...
-4
votes
1answer
56 views

What is an example of asymmetric cryptography?

What is an example of asymmetric cryptography or public key cryptography?
-1
votes
1answer
261 views

how to encrypt the chat message with multiple people public key together and restore the message?

I have a application with two users and one middle man, all of them holding the private and public key, To make the secured chat, two users and one middle man are all sending the public key and ...
0
votes
1answer
152 views

Curve25519 simple key exchange approach

What is a simple approach in Curve25519 key exchange in basic steps?
2
votes
1answer
296 views

Is it possible to implement the Signal Protocol without a server?

My question is regarding the Signal Protocol[1]. Is it possible to implement the protocol securely, without a server? (I have no particular motivation for the question other than to understand better ...
0
votes
1answer
36 views

relationship between equivalent ways of computing RSA private key

I have found two ways to compute the RSA private key, but i have trouble understanding why they are equivalent. $1) D={k \phi(N)+1 \over E}$ $2) E* D=1 \mod \phi(N)$ $1)$ AFAIK comes from taking ...
1
vote
1answer
97 views

Is MAC required with Sign-then-Encrypt?

Consider a scenario where a message is sent encrypted and signed using public-key cryptography. When using asymmetric encryption, you end up also using symmetric encryption if the message is large (...
0
votes
0answers
35 views

encrypytion schemes which commute under self-composition

Talking with some friends we arrived at following puzzle: Alice wants to send Bob some message, but Alice has to make sure that some condition is met before allowing Bob to read the message. This is ...
3
votes
1answer
188 views

Is there a lower cost cryptography than elliptic-curves based cryptography?

ECC requires less CPU power, less memory and shorter keys than RSA or any other asymmetric cryptography I came across in the literature (correct me if I am wrong). Is there a lower cost asymmetric ...
0
votes
0answers
40 views

public encryption / message verification algorithm with efficient decryption

I'm looking for an asymmetric key'd encryption method for passing a security token. The security token will hold some information about the users credentials encrypted, allowing the receiver of the ...
12
votes
4answers
3k views

Efficient hardware implementation of real-time asymmetric video encryption

I want to encrypt video directly at the source where it is being captured, e.g. inside a video camera. This way I can transmit the encrypted stream over WiFi securely. I could use AES on the chip ...
2
votes
1answer
57 views

Can messages be recovered from signatures if the private key is known?

If the message that was signed with a digital signature is not known, can it still be recovered if you have the private key?
0
votes
0answers
46 views

$c = d \oplus (f(d)\parallel p)$, solve for $d$ and $p$, how many solutions could you find?

$d$ is $2n$-bit and truly random, $f(d)$ and $p$ are $n$-bit, $f:\{0,1\}^*\to\{0,1\}^n$ is a digital signature with a public-private key pair, and $p$ is that public key. For a value $c = d \oplus (f(...
0
votes
1answer
546 views

How does RSA public and private key structure look like?

So I was reading this wiki about the RSA algorithm and I read this article to understand it better. My goal was to create a simple program that would generate private and public keys. I got to the ...
0
votes
2answers
122 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?
1
vote
2answers
74 views

CSPRNG generation vs asymmetric encryption performance

It might sound like a weird comparison, but which one is faster, If I were to generate a CSPRNG every time or to sign(private encrypt) a data?
0
votes
0answers
21 views

Alternative Hard Problem to Prime Factorization? [duplicate]

Suppose in the future someone conjures a technique to (arbitrarily) quickly find the prime factors of arbitrarily large numbers, thus undermining the computational security of (as far as I am aware) ...
2
votes
1answer
101 views

Keyspace of asymmetric ciphers. (RSA)

I have difficulty finding information about key space calculation of RSA. I think there is a gap in my math knowledge that prevents me from understanding the problem. I know that symmetric ciphers ...
4
votes
1answer
69 views

How to prove that a hash or an encrypted message was obtained from a plaintext that has a certain pattern?

I have the following idea of implementing a lottery game: we have all the numbers from 1 to 40 we generate a permutation of those numbers which will be the lottery solution participants need to guess ...
2
votes
1answer
52 views

Role of long-term asymmetric keys in a forward secrecy instant messaging protocol?

I am trying to understand how forward secrecy works in general, using a simple instant messaging protocol as an example. Tell me if I have this process right or not: 1) Alice and Bob each generate a ...
2
votes
0answers
30 views

Encryption design for user data with service access

I'm looking to provide users with a way to give a service sensitive information, which the service can freely use up until the user decides otherwise. I want to encrypt the data at rest (and of course,...
1
vote
3answers
146 views

Explaining RSA to non-scientists

I am to give a small lecture on quantum computing in a months' time and I want to shortly give an intuition to the fact that Shor's algorithm shows that quantum computers will break RSA. Ideally, I ...
1
vote
2answers
73 views

How to cipher with N public keys and decipher with ANY of the N private keys?

X = plaintext Given N key pairs: P1 = (P1.private, P1.public) ... PN = (PN.private, P1.public) I want to find 2 function Cipher and Decipher such as ...
2
votes
2answers
124 views

Multiple Keys for an Encrypted Secret

I have the following problem: I want to put a document on a ipfs store. So it is accessible via a distributed network. Now, at first only two persons (Alice & Bob) should have access on the file. ...
0
votes
0answers
27 views

Encrypt data between unsafe API

I have client-server application that communicates like this: Client sends data to API1, then API1 proxy that data to API2: Client <-> API1 <-> API2 ...
3
votes
1answer
81 views

should one worry about timing attacks with signature verification?

To compare two varablies in such a way that timing attacks don't exist it's generally recommended you pad the strings to the same length and then look at each byte, even if an earlier byte was ...
5
votes
2answers
1k views

Why is Diffie Hellman used alongside public keys?

I just read this post here: Why do we need asymmetric algorithms for key exchange? that asserts that in public key cryptography when asymmetric keys are used to secure communications, for parties to ...
0
votes
1answer
84 views

Encrypt or decrypt using the private key, and decrypt using the public key?

I am currently trying to figure out if my following scheme is implementable in ECC or whether I can use existing implementation. At first I was going with libsodium but it seems that it really doesn't ...
2
votes
2answers
478 views

What is the benefit of zero knowledge identification (Fiat Shamir) over a standard digital signature?

Let's say there is a public key $v$. Peggy has to prove to Victor that she has the corresponding private key $a$. Of course she doesn't want to disclose $a$ to Victor, but just to prove that she has ...
10
votes
2answers
601 views

Modular Inverse as a Problem

Given a modulus $N$ and a number $a$, a multiplicative inverse exists for $a$ if $a$ and $N$ are coprime. Why isn’t there a cryptosystem that uses this as a computational problem? Example Alice and ...
1
vote
1answer
226 views

How does Naver Line PC client obtain private key for end-to-end encryption (letter-sealing)?

When I download Naver Line PC client onto my PC, a six-digit number will be shown on the PC client for me to enter the number into my Line app on my mobile phone for decrypting the old and new ...
0
votes
2answers
77 views

If a private key decrypts what its public key encrypts, can the public key conversely decrypt what its private key encrypts?

Whilst studying the material for the CCNAS exam, I have encountered something on the cryptographic systems chapter that I am not sure about. Cisco Netacad states that "Asymmetric algorithms use two ...
2
votes
1answer
80 views

Diffie Hellman: Why is $(\mathbb{Z}_{8191}^*, \times)$ an insecure group?

I noticed that all the binary bits of $8191$ are $1$'s. Could this have something to do with it?
6
votes
1answer
2k views

WhatsApp end-to-end encryption

WhatsApp offers end-to-end encryption. However, when I start using it on a second device such as a PC running Windows, I can decrypt incoming messages without providing any private key into my second ...
0
votes
0answers
32 views

Digital signature certificate limited validity period

Digital (or electronic) signature certificate can have limited validity period - 1 year for example. I wonder how this is done technically in asymmetric cryptography. Can someone explain? Say I have ...
0
votes
1answer
183 views

Group signatures, security and ECDSA

I am reading up on group signatures. With RSA a public key can have more than one private key. For a public exponent $e$, private exponent $d$ and modulus $n$, there is more than one solution for the ...
1
vote
0answers
154 views

BLS aggregate signatures for relay node non-interactive incentive accounting

This is a practical application of cryptography question and I hope this is the right place to ask it. Any advice would be very much appreciated. I'm looking for a low-bandwidth, non-interactive ...
0
votes
0answers
108 views

Division of a number in Paillier encrytion which yields decimal result

I am very new to start with Paillier encryption system. I have used the homomorphic nature of this scheme, which allows addition of two encrypted numbers. I was wondering is it possible to divide two ...
0
votes
1answer
231 views

Best method to achieve authenticated encryption with openssl

Problem I want to send a plaintext document between from myself to someone else over an untrusted link. I want to firstly stop third parties from reading the document, I want the receiver to be able ...
1
vote
2answers
64 views

Is it impossible to have a decentralized service using email addresses as login?

Let's say we have a decentralized service S distributed on a network of 1000 nodes/servers. Is it possible to have a registration/sign up scheme using email address ...
2
votes
1answer
255 views

Public key homomorphic encryption based on secret key homomorphic

Let $(E,D)$ be a secret-key bit-encryption scheme that is homomorphic to xor, and assume that each bit encryption is of size n (this concerns both fresh encryption and encryptions that have been ...
-1
votes
1answer
565 views

Java recover the public key by only having the privatekey possible? [closed]

Source: https://stackoverflow.com/questions/48521925/java-recover-the-public-key-by-only-having-the-privatekey-possible How to solve this problem programmatically ...
0
votes
0answers
30 views

one-NAD-SIM to many-NAD-SIM for public key encryption

In public key setting we know that one-IND-security gets many-IND-security. I mean if we can prove the security for one ciphertext-challenge then we are sure about security for many ciphertexts by ...
3
votes
2answers
1k views

When is the public ECC key generated?

I have been learning about the fundementals of ECC and I'm a bit confused on this point: What makes up the public key in an ECC key exchange, and when is this public key generated? In the video at ...