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Questions tagged [diffie-hellman]

The Diffie–Hellman key agreement is an anonymous, non-authenticated key-agreement protocol.

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Good Diffie-Hellman Encryption Method

I've just made my own implementation of Diffie-Hellman in nodejs (it's for a project of mine). However, the shared keys are integers; I want to use those integers as a key to encrypt data. This is an ...
-2 votes
2 answers
1k views

How to find at least one private key from a large list of compressed public keys secp256k1

Not long ago I saw a discussion on the Bitcoin Talk forum: https://bitcointalk.org/index.php?topic=5060735.msg50736695#msg50736695 Please give advice and working methods? Is it possible to find at ...
0 votes
1 answer
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diffie hellman key exchange compared with ECDH [closed]

I have to write a paper about the Diffie Hellman key agreement. I want to focus on the implementation with elliptic curves and comparing the safety for selected attacks such as Pollards Rho and ...
2 votes
2 answers
82 views

On a diffie hellman related oracle

Given an oracle that can compute $g^{x^{-1}}\bmod p$ from $g^x\bmod p$ is it possible to compute $g^{x^2}\bmod p$ in polynomial time ($p$ is a prime and $g$ generates the multiplicative group modulo $...
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How some auxiliary information influence the CDH assumption?

I am proposing a multi-party group-key agreement protocol in my paper, which can be seen as an extension of the classic Diffie Hellman bipartite group key agreement. However, how to formalize the ...
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1 answer
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Is shared secret and SKEYID are same in the IPSec?

I want to know that, is shared secret and SKEYID are same in the IPSec? I knew that from SKEYID, three further keys are generated (derivative, authentication and encryption). But from where this ...
4 votes
3 answers
2k views

Why does Diffie-Hellman need be a cyclic group?

Why is Diffie-Hellman defined on a cyclic group? Doesn't it work for any commutative operation which the inverse is hard to find? Say Alice and Bob agree in a public prime $c$ and both choose a ...
4 votes
2 answers
108 views

How do I solve a discrete log using pen paper for exam without bruteforcing it?

I have my Network Security finals. In elgamal cryptosystem, I am often encountering these equations like this 3 = (10^XA) mod 19 now everywhere I am finding only ...
1 vote
1 answer
70 views

What's the difference between these two attacks?(Lim Lee and Sub group) I am a beginner can someone explain in detail?

I am reading collin boyd textbook to learn MTI key agreement and various attacks on them . I encountered two such attacks called Small sub group attack and Lim-Lee attack where in Small sub group ...
1 vote
3 answers
176 views

mutual authentication in STS protocol

STS Protocol is like this: $A \rightarrow B:~ g^x$ $A \leftarrow B:~ g^y, E_K(S_B(g^y, g^x))$ $A \rightarrow B:~ E_K(S_A(g^x, g^y))$ My question is why do we say in STS we have mutual authentication?...
6 votes
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Why does it take longer to generate suitably large primes for Diffie-Hellman key exchange as opposed to for RSA encryption / decryption?

For RSA, we need two primes p and q to define N = pq. We will only look how long it takes to generate a prime for p because the process is similar for q. From my lecture slides, my professor states ...
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1 answer
183 views

Authentication Fold-In in Oracle Database

The Oracle database has a feature known as "Native Network Encryption". It is a protocol described as a 4-step procedure. Step 1 : Negotiate parameters for following steps Step 2 : Exchange ...
1 vote
1 answer
70 views

Is it possible to use Diffie-Hellman protocol for symmetric group?

I was asked this question during one of my first cryptography classes, and I'm not sure if I understand it correctly. To begin, I know that after using the Diffie-Hellman protocol (which itself is ...
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Sending public key trough untrusted server

I am developing end-to-end encrypted chat system (which is open-source). When I want to give other client my public key, I need to send it trough server, right? I want to make sure no one can edit the ...
3 votes
1 answer
198 views

Can DH be used for privacy-preserving proof of possession?

First time question poster so I hope the below is clear enough :). Problem summary: Can a Holder and Verifier safely use ECDH for a Challenge-Response protocol where: the Holder proves possession and ...
2 votes
1 answer
113 views

Is Message Layer Security the state of art protocol for group encryption?

I'm trying to read about Diffie Hellman (One to One) kind of protocols for group communication. Is Message Layer Security the state of art protocol for group encryption (not necessarily chat or ...
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Curve448 ECC parameters for use with OpenSSL

I need to be able to deterministically generate (and re-generate) private-public ECC key pairs curve448 for ECDH from human-friendly passphrases (not necessarily human-memorable, just easy to type in),...
1 vote
1 answer
144 views

A simple guide to Diffie-Hellman Key Exchange including the what, the how and the why

I'm tired of going online looking for a simple explanation of how the Diffie-Hellman Key Exchange works. Many guides I've found attempt to explain it using anything from "paint" to massive ...
0 votes
1 answer
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How to handle IKEv1 and IKEv2 diffie-hellman shared secret bits length not multiple of 8 in ACVP

Hi I found this question which I am currently struggling with. How to handle IKEv1 and IKEv2 diffie-hellman shared secret bits length not multiple of 8? In ACVP, the input diffe-hellman shared secret ...
1 vote
2 answers
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App for Secure delivery of the gray images using AES, DH, DSA - Help in implemeting the system structure

I have this uni project that I have to implement in code: "App for Secure delivery of the gray images, encryption-decryption with AES in OFB mode + secret key delivery using Merkle–Hellman ...
0 votes
1 answer
56 views

TLS 1.3 digital certificates and ephemeral Diffie Hellman

There is a lot of confusing information out there regarding the role of digital certificates and the use of Ephimeral Diffie Hellman in how TLS 1.3 operates. Would it be correct to state that the the ...
0 votes
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254 views

Post-quantum hybrid encryption

Assume the following simplified protocol: seed = curve25519SharedKey(theirPublicKey, myPrivateKey) sharedKey = scrypt(seed, salt, sufficientlyHardWorkFactors...) cipherText = aes256(sharedKey, ...
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Inquiries on Strong Diffie-Hellman assumption

According to the SDH assumption, it is hard for an adversary to output a pair $(c,g_1^{\frac{1}{c+\alpha}})$ given a $q+2$ tuple ($g_1$,$g_2$,$g_2^{\alpha}$, ...,$g_2^{{\alpha}^q}$) Now, consider $g_1$...
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Generating a new curve using an existing curve and new prime

Can you take a curve equation from https://safecurves.cr.yp.to and a large safe prime from existing DH parameters (for example openssl dhparam 9000), combine them, ...
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Secure key exchange for custom USB device

I'm learning various cryptography protocols and use cases and since I'm developing a USB device and PC application, it would be nice to use encrypted communication. I studied TLS 1.2 key exchange but ...
10 votes
2 answers
2k views

Summarize the mathematical problem at the heart of breaking a Curve25519 public key

It's pretty easy to generate a Curve25519 private key: generate 32 random bytes of data and then do: e[0] &= 248 e[31] &= 127 e[31] |= 64 You can then ...
2 votes
2 answers
90 views

One group element hybrid encryption for El Gamal

I am really curious about this one problem 10.12 from Katz/Lindell's book. It goes as follows: I am quite sure we can assume that $\textsf{Enc}_k(m) \in \mathbb{G}$, as the authors devoted the whole ...
4 votes
1 answer
883 views

What is a u-coordinate within Elliptic Curve Diffie-Hellman using the Montgomery ladder

I am trying to understand the below paragraph. Elliptic curve Diffie-Hellman is often calculated using the Montgomery ladder. This gives a simple and efficient calculation that is naturally ...
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366 views

Are Safe and Sophie Germain primes evenly distributed?

Do Safe and Sophie Germain primes maintain a relatively stable distribution as numbers get larger, or do they become rarified beyond a predictable value? This is important in one area of triangular ...
1 vote
1 answer
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Use of CertificateVerify in TLS_DH_RSA with client authentication?

Does anyone know if CertificateVerify is sent in TLS_DH_RSA with client authentication? Does anyone know the RFC or could explain the meaning of it? With TLS_RSA, a ...
1 vote
1 answer
87 views

Signed vs unsigned prekeys

I am trying to understand the signal protocol better. I spend some time trying to understand their codebase (the backend is written in java). The signal protocol indicates that the user has to upload ...
1 vote
2 answers
159 views

Is this self algorithm made private key for Diffie-Hellman key exchange secure

i created a function in javascript that creates my a for the DH exchange like this: ...
4 votes
4 answers
10k views

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 ...
1 vote
1 answer
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Similar to Diffie Hellman for BLS in asymmetric pairing?

I had asked one question before One-More Computational Diffie-Hellman in asymmetric pairing groups and have not received answer. I am posing a supplementary question now that I just realized I don't ...
2 votes
3 answers
238 views

Is any safe prime sufficient for a secure DH key exchange?

There are some very large safe primes listed here: https://en.wikipedia.org/wiki/Safe_and_Sophie_Germain_primes Would using any of them result in a secure DH construction? Generator is 2. The exponent ...
2 votes
0 answers
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Tor Key Exchange Client - Middle Node

I am currently exploring the workings of the Tor network, specifically how the Diffie-Hellman (DH) key exchange protocol is employed to establish shared secret keys between the client and each relay ...
7 votes
1 answer
721 views

Why is this authenticated Diffie–Hellman key exchange insecure?

I was searching for the information on authenticated Diffie–Hellman key exchange and found these slides. The author says, “Remember $$A\to B: (A, g^x, \operatorname{SIG}_a((g^x, B)))$$ $$B\to A: (B, g^...
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which DH protocol is safer in communication with given condition?

I am trying to understand some concepts such as DH problem and its variants. I have the following question from the book I read. (note that I translated the question from my language to english) ...
3 votes
2 answers
3k views

Static vs ephemeral diffie-hellman

I feverishly searched the web and couldn't find a clear explanation about what exactly is "Ephemeral diffie-hellman". Let's briefly recall how diffie-hellman basically works: Bob and Alice ...
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Distinguishing between two DDH-like tuples

Given a group generator $g$ (in a group where DDH is hard). Let $X_1=g^{x_1}$ and $X_2=g^{x_2}$ be two public elements, where $x_1$ and $x_2$ are selected randomly and kept secret. Consider a game ...
1 vote
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Can the byte overhead of an ECDH based hybrid cryptosystem be reduced by encoding data in ephemeral key?

Motivation I have a use case that involves sending small (25-50 byte) encrypted messages over a very constrained channel. Many senders send public key encrypted messages to other receivers. Anonymity (...
1 vote
1 answer
382 views

DHKE: Why using safe prime gives us "safe" subgroups?

I come from the question here: Safe primes subgroup in Diffie–Hellman key exchange Where the accepted answer states that there are only 4 possible outcomes for the order of a subgroup when using a ...
2 votes
3 answers
987 views

Where is Challenge/Response and Certifcate Verification in TLS-DHE

We have been give a task to identify the following three components in TLS-DHE: Diffie Hellman Key Exchange I am fairly certain that this Part can be found in the Exchange of SKE and CKE, since they ...
3 votes
2 answers
202 views

What is the difference between Post-Compromise Security and Backward Security?

Post-Compromise Security and Backward Security seem to mean that the attacker has obtained the communication key between two parties or groups in the current state, but cannot further obtain ...
5 votes
3 answers
7k views

Diffie-Hellman algorithm and MITM attack

How does the Diffie-Hellman algorithm prevent MITM attack? I have tried to search about it but i couldn't find any understandable reasons.
2 votes
1 answer
356 views

Diffie-Hellman with Galois field

I Google around and can't find any page mentioning Diffie-Hellman with Galois field $GF(p^n)$ with $n>1$. Is there a reason for this? For example, wouldn't Diffie-Hellman with $GF(2^n)$ be ...
3 votes
1 answer
158 views

Separation between CDH and DDH

Do there exist cryptographic primitives that have proved that they cannot be constructed from CDH assumption only but can from DDH assumption? More generally, do there exist cryptographic primitives ...
1 vote
1 answer
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How often do Double ratchet in Signal protocol update DH ratchet key

I'm trying to understand the specification behind doubleratchet algorithm, item 2.4. Double Ratchet. According to wiki: A client renews session key material in interaction with the remote peer using ...
4 votes
1 answer
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How does the Legendre symbol reveal if $g^a$ is odd or even for Finite Field Diffie-Hellman

According to wikipedia(markdown is striped below) for Decisional Diffie–Hellman assumption: the DDH assumption does not hold in the multiplicative group $Z(p)$, where $p$ is prime. This is because if ...
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Could ECDH-OPRF-PSI support private information retrieval?

Alice:has $x=(x_1,x_2,...x_m)$ Bob: has $(y_1,m_1),...,(y_n,m_n)$ For this, Alice wants to get some message from Bob, but does not want bob to know which one she gets Bob generate random $a \in Z_q$,$...

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