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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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Why using q = (p - 1)/2 for discrete log Diffie-Hellman scalar operations and not p?

As defined in RFC 3526 the prime $p$ and generator $g$ are known. The prime $p$ defined there is a safe prime, which can also be expressed as $p=2q+1$ with $q$ prime. The amount of elements in this ...
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DH Encrypt by XOR

I'm working in the Curve25519 domain (EC curve, 256-bit key size). I have a peer pubkey, and need to send it an encrypted message. For starters we create a "nonce" (ephemeral key), and use ...
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How do I find the order of the subgroup in a Diffie-Hellman key exchange?

I'm implementing the Diffie-Hellman key exchange as specified in RFC 4253 for SSH. Here's an extract from the RFC: The following steps are used to exchange a key. In this, C is the client; S is the ...
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Proof that Inverse CDH and Square CDH are equivalent

I am trying to prove said equivalence, but when proving SCDH -> ICDH using a reduction, I get stuck since I don't know how to compute $g^{x^2}$ starting from $g^{x^{-1}}$. Suppose exists $A_{ICDH}$ ...
Pietro D'Amico's user avatar
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Is the following Inverse Computational co-Diffie-Hellman problem hard?

Let $\langle g \rangle \stackrel{\Delta}{=} \mathbb{G}$ and $\langle h \rangle \stackrel{\Delta}{=} \mathbb{H}$ be groups of prime order $p$. Given $( p, g, g^\delta, g^{\delta^{-1}}, h, h^\delta )$, ...
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Safety per bit DHKA and ECDH

I have a project where I compare the classical Diffie Hellman key agreement with its implementation with elliptic curves. Therefore I need a list with the safety per bit. Does anyone know where I can ...
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Is the MITM protection provided by BLE LESC passkey mechanism bidirectional?

I'm trying to understand whether the passkey mechanism described in BLE LESC pairing provides bidirectional MITM protection. As far as I understand, A and B will generate the same shared secret using ...
cheapjuice's user avatar
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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 ...
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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 ...
glietwp's user avatar
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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 ...
Tech Learner's user avatar
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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 ...
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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 ...
nasiedlak's user avatar
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1 answer
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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 ...
karolajoj_PL's user avatar
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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 ...
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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 ...
ENGO_150's user avatar
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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),...
Logan R. Kearsley's user avatar
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2 answers
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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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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 ...
suchislife's user avatar
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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 ...
Mustafa Shama's user avatar
3 votes
1 answer
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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 ...
Peter Altmann's user avatar
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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 ...
termcap's user avatar
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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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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 ...
unalignedmemoryaccess's user avatar
2 votes
2 answers
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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 ...
Michael Hammer's user avatar
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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 ...
user946822's user avatar
1 vote
1 answer
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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 ...
Farhan Syedain's user avatar
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2 answers
161 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: ...
Moritz Fesseler's user avatar
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1 answer
68 views

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 ...
Manish Adhikari's user avatar
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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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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 ...
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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 ...
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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) ...
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397 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 ...
Zekchelovek's user avatar
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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 ...
Doron's user avatar
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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 (...
Richard Thiessen's user avatar
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1 answer
400 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 ...
Ymi's user avatar
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2 answers
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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 ...
Guardzhan's user avatar
3 votes
1 answer
161 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 ...
misosiru's user avatar
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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 ...
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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 ...
pacman's user avatar
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1 answer
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Safe primes subgroup in Diffie–Hellman key exchange

I'm trying to understand how the safe primes numbers are used in Diffie–Hellman key exchange. According to wiki: The order of G should have a large prime factor to prevent use of the Pohlig–Hellman ...
pacman's user avatar
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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 $a \in Z_q$,$...
haoxuan li's user avatar
1 vote
2 answers
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Efficiently detect that a ciphertext is meant for Alice

Assume we have the situation that Alice is receiving somewhere in the magnitude of 1_000_000 encrypted messages, whereby a small number (n<100 for 99% of cases) of these messages are meant for her. ...
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1 answer
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Does TLS1.3 support DHE_EXPORT cipher suite? [duplicate]

I just wanted to know for sure that TLS 1.3 does not support DHE_EXPORT cipher suits.
warren's user avatar
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Why does ECIES use "Key Encapsulation"? Does it?

In yet another twist that is the terminology around key establishment I found out that ECIES is often denoted as key encapsulation followed by data encapsulation. I'm wondering how the term "key ...
Maarten Bodewes's user avatar
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In TLS 1.2 and TLS 1.3, does the EC curve used to generate the ephemeral keys be the same on both client and server sides?

In TLS 1.2 and TLS 1.3, does the EC curve used to generate the ephemeral keys at the client side, does it need to be the same as that on the and server sides? For example can I use secp521r1 at the ...
warren's user avatar
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1 answer
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On a problem assuming Diffie-Hellman oracle

If we have a Diffie-Hellman oracle then given $g^x$ and $g^y$ we can construct $g^{xy}$. Can we construct $g^{x^{-1}}$ given $g^x$?
Turbo's user avatar
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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 ...
Genie's user avatar
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1 answer
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What is the correct way to use HKDF with X25519?

I am trying to implement ECIES properly with X25519/HKDFwithSHA256/AES-128-GCM with Node.js crypto library. It is not clear to me how to determine the input key material (IKM) to HKDF. Initially, I ...
Eri's user avatar
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3 votes
1 answer
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Does ECDH on secp256k produce a defined shared secret for two key pairs, or is it implementation defined?

Rust and NodeJS implementations of ECDH on secp256k1 produce different shared secrets, when using identical keypairs: NodeJS: ...
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