What's the deal with Deno? We talk with a major contributor to find out. Listen now.

Questions tagged [diffie-hellman]

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

Filter by
Sorted by
Tagged with
0
votes
1answer
33 views

Why is private key chosen to be less than chosen prime in diffie-hellman?

since the public key is calculated as Y=(alpha^private-key)mod(chosen prime) and alpha is a primitive root of prime, when Y becomes public then private key can be calculated easily right? since there ...
0
votes
1answer
36 views

Is it possible to safely implement the Signal Protocol (X3DH) without using XEdDSA

In the X3DH specification of the Signal Protocol it mentions having a signed pre-key in the key bundle. This pre-key is signed using the identity private-key. Because the identity private-key is in ...
1
vote
1answer
32 views

Asymmetric Encryption vs Shared secret via ECDH

I'm reading RFC8291. Here's a figure on how Web Push Notifications work in general: ...
0
votes
1answer
63 views

Proof of (in)distinguishability based on DDH/CDH/DL

I am wondering whether or not it is known that the following problem is computationally infeasible while working in a group for which the DDH (or CDH or DL) assumption holds (as usual, g is a group ...
0
votes
1answer
35 views

Is BBS+ 1. a multi-messages signing protocol or 2. a group signature signed by a member of a group anonymously?

There's no doubt that the BBS Signature was born from this classic Short Group Signature paper in 2004. It's capable of Zero-knowledge. In the paper, section 5, it describes how a member of a group, ...
2
votes
1answer
57 views

In q-SDH problem, where are those points $\frac{1}{\beta+x}g$ or $g_1^\frac{1}{x+c}$ on elliptic curve?

For the q-SDH problem, given the generator $g_1$ as a point on the elliptic curve, I can picture the $\beta g_1, \beta^2g_1, ..., \beta^qg_1$ since we can simply do the point adding $g_1$ multiple of $...
1
vote
1answer
515 views

DH Elliptic Curves: Why choose a fixed base point?

I am having a first look at the TLS key exchange using Diffie Hellman and try to understand the Elliptic Curve variant of it. So if a client and a server agree on using ECDH for key exchange and they ...
2
votes
0answers
39 views

Security problems if ECDH and ECDSA use the same key [duplicate]

Hy! I want to use an EC key for ECDH and ECDSA too. Using the same key does compromise the security of the key in a cryptographic / mathematical sense? I read a lot in this theme, but I found nothing ...
0
votes
1answer
49 views

Can I use the same key pair for authentication and Diffie-Hellman? [duplicate]

Assume Alice has a key pair $(A, a)$ and Bob has a key pair $(B, b)$, where $A = Ga$ and $B = Gb$. In general, the basic rule of crypto says that we should not use the same key for different ...
7
votes
0answers
117 views

About a SETUP mechanism on ECDH

I'm following these three articles: Kleptography: Using Cryptography Against Cryptography, Kleptographic Attack on Elliptic Curve Based Cryptographic Protocols and Elliptic Curve Kleptography . In ...
0
votes
1answer
44 views

Key generation for DH key exchange - benefits of using KMI

Context We need to generate a key pair in order to perform DH key exchange with the other party. Some suggest to use a KMI solution (think: AWS KMS or like) in order to generate the key pair. ...
6
votes
1answer
218 views

What information is revealed if we send our points in Projective Coordinates?

Elliptic Curve Cryptosystem has various coordinate systems; like the Affine, Projective, and Jacobian coordinate systems. We prefer not to use the Affine coordinate system during the calculations ...
0
votes
1answer
85 views

why to use a safe-prime in Diffie-Hellman key exchange?

In order for Diffie-Hellman to be extra secure we must use a safe prime which is (p – 1) / 2 will also be a prime. so my question is what extra benefit of using ...
1
vote
1answer
92 views

ECIES for encrypting ECDH key exchange

I started studying Elliptic Curve Cryptography, and I do not know if I understand the difference between ECDH and ECIES (even with the other posts here on stackexchange). I'm wondering if ECIES can be ...
1
vote
1answer
66 views

Safe primes and subgroups

I've been reading about safe primes and their use in: Cryptography Engineering by Niels Ferguson, Bruce Schneier, and Tadayoshi Kohno. Having a safe prime $q$ with $q=2p+1$ where $p$ is a Sophie ...
2
votes
1answer
91 views

Diffie-Hellman Private Key Size

I'm currently writing my own implementation of Diffie-Hellma n(This isn't for actual use. This is strictly for me to get a better understanding of DH by doing it myself.) For the prime and generator, ...
2
votes
1answer
54 views

Significance of y-coordinates in ECDH public key exchange

In the research paper Breaking the Bluetooth Pairing – The Fixed Coordinate Invalid Curve Attack? by Biham and Neumann, 2019, they talk about attacks in Bluetooth pairing, they state that in the ...
0
votes
0answers
43 views

Show all the messages exchanged between Alice and Bob using the three-pass Diffie-Hellman protocol

PROBLEM STATEMENT: "Suppose that users Alice and Bob carry out the 3-pass Diffie-Hellman protocol with p = 101. Suppose that Alice chooses a 1 = 19 and Bob chooses b 1 = 13. If Alice wants to ...
2
votes
1answer
79 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^...
4
votes
1answer
148 views

Diffie-Hellman: difficulty of computing $g^{x^2}$ given $g^x$?

Hoepfuly a simple question. Given a group where the CDH problem is hard, if the adversary sees a public key $g^x$, is it easy or hard for the adversary to compute $g^{x^2}$? My intuition says it ...
6
votes
1answer
116 views

Should I use self generated or predefined RFC 7919 DH groups?

On a wiki page, archived by now, Mozilla switched from recommending self generated DH groups to the ones predefinded in RFC 7919. The recommendation was accompanied by the statement These groups are ...
0
votes
1answer
58 views

Has the ECDH protocol been designed just for key exchange or is it widely used for key exchange?

As far as my understanding of the ECDH goes, after systems are encrypted using ECDH protocol, any data that comes out of the first system will be encrypted and can only be decrypted at the receiving ...
2
votes
0answers
92 views

Curve25519 Attacks and Security

Curve25519 is a pretty secure way to exchange a key. In the original Paper and on SafeCurves a lot of attacks and security aspects are mentioned: Attacks: Brute force: This one is theoretically ...
1
vote
1answer
54 views

MQV protocol and man-in-middle attack

Why MQV is said to be an “authenticated Diffie-Hellman” protocol? The process in the picture shows nothing about authentication. Besides, a man-in-middle can impersonate B to negotiate with A, because ...
1
vote
1answer
48 views

I want to know the hardness of computing a or b given $g^{b^{-1}}$ and ab in cyclic groups with large prime order

$G$ is a multiplicative cyclic group of a large prime order $p$ and $g$ is a generator of $G$ Theorem 1: Given $g^{b^{-1}}$ and $ab$, it's hard to compute $a$ or $b$, where $a$ and $b$ are randomly ...
7
votes
1answer
506 views

How do client and server agree on the values of p and g during DHE exchange?

How do the communicating parties using Finite Field DHE agree on the values of the $p$ and $g$ variables? Are their values fixed for each DHE group? Reading through the TLS 1.3 RFC (8446), the client ...
11
votes
1answer
206 views

What is this problem called and is it hard? given $g^x$ output ($g^y, xy$)

Assume that $G$ is any cyclic group where the discrete log problem is hard, such as the elliptic curve group. Let $g$ be some generator of $G$. The problem is as follows: Given $(g, g^x)$ for unknown $...
3
votes
0answers
69 views

Key strength comparison: symmetric key vs RSA/DH key

I came across different reputable sources quoting different equivalent symmetric key strengths for RSA/DH keys. This NIST paper (page 67) states the following offer corresponding security strenghts (...
2
votes
2answers
220 views

Diffie-Hellman key exchange, then so what?

I know how the Diffie-Hellman Key Exchange (DHKE) works. But where is it used? And ok, now both have the same key. But how are those keys used anyway? I've heard that HTTPS is using the DHKE. Ok, but ...
0
votes
1answer
117 views

Why discrete logarithm modulo composite moduli not popular and not defined in standards?

The classical discrete logarithm problem is to find $x$ such that $g^x\equiv h\bmod p$ where $p$ is a prime and $g$ is generator of multiplicative group modulo $p$. The demerit of this approach seems ...
1
vote
0answers
24 views

How to handle IKEv1 and IKEv2 diffie-hellman shared secret bits length not multiple of 8?

In Cryptographic Algorithm Validation Program for KDF document, here, page 9, it says "If a field size that is not a multiple of 8 bits, the shared secret is represented by a string of bytes that ...
3
votes
1answer
56 views

What is the exact meaning of the public key cryptosystem properties in New Directions In Cryptography by Diffie and Hellman

I'm quite new to cryptography and don't have much mathematical knowledge. I'm studying cryptography, especially public key algorithms. I have some basic knowledge of public key algorithms so I know ...
0
votes
0answers
54 views

Why the standard DH is not sufficient to ensure the security of the Diffie-Hellman key exchange?

I don't know mucho about Cryptography, I try to understand, It's for homework. Why the standard DH is not sufficient to ensure the security of the Diffie-Hellman key exchange? My answer was: In the ...
0
votes
2answers
123 views

How to encrypt with elliptic curve cryptography (ECC)?

I need to ask this, as I am not allowed to comment and don't quite understand an existing answer because I don't have a cryptography background and never looked into how ECC works. Why can't you ...
0
votes
0answers
21 views

Can we use HMQV in an asynchronous setting?

Following the HMQV paper, to perform a key-exchange, Alice ($\hat{A}$) and Bob ($\hat{B}$) perform the following: $\hat{A}$ generates the long-term key pair ($sk_A= a$, $pk_A =g^a$) and the ephemeral ...
1
vote
0answers
39 views

Non-interactively share secret with group without revealing to generator?

Imagine someone knows a set of $n$ ECC public keys $\mathcal R = \{K_1, K_2, ... K_n\}$ but they don't know the corresponding private keys $k_1$, $k_2$ ... $k_n$. They wish to create a public key $sG$ ...
3
votes
2answers
820 views

Encryption and decryption with Diffie-Hellman

I don't understand how it works. I only found explanations about the key exchange, but what about the actual encryption and decryption? Do you use the session key $K$ with a symmetric algorithm? Do ...
1
vote
0answers
68 views

is it possible to achieve authenticated key agreement without using PKI or pre-shared secret?

After reading different techniques to achieve authenticated key-agreement (X3DH, HMQV, Asynchronous Ratcheting tree, An efficient protocol for authenticated key agreement, I understood that all these ...
1
vote
2answers
59 views

SIKE as Diffie-Hellman exchange

SIKE involves a Diffie-Hellman like construction using isogenies between elliptic curves. Is it possible to express it as an instance of Diffie-Hellman? I.e. what is the underlying group if so, and ...
0
votes
0answers
27 views

Steiner GDH3 (n-party Diffie Hellman)

I am trying to implement a n-party Diffie Hellman protocol. In particular I'm implementing Steiners et. al. natural extension "GDH3" (starting on page 34). The problem is that my python ...
0
votes
1answer
57 views

Diffie-Hellman Decryption with A, B, p, g, cipher Parameters

I have a Crypto assignment, trying different ideas for couple hours landed me nowhere. Supposedly during a Diffie-Hellman key exchange Alice sends bob an encrypted message, the message (cipher) is a ...
0
votes
1answer
62 views

Diffie-Hellman parameter for use in TLS derived from given finite-field group

I'm interested in cryptography, but unfortunately haven't found the time to dive into the topic much. I have done some quantum encryption stuff back in the day, but that isn't helping me with my ...
3
votes
0answers
125 views

Why Kerberos isn't using Diffie-Hellman key exchange?

Kerberos transforms the user password to obtain a secret key, which is also stored in the kerberos database. That way what travels through the network is the derived key, not the password itself, ...
1
vote
0answers
60 views

Change in Diffie-Hellman

In the Diffie-Hellman protocol, each participant selects a secret number $x$ and sends the other participant $α^x\bmod q$ for some public number $α$. What would happen if the participants sent each ...
0
votes
0answers
36 views

Secret keys in Diffie-Hellman

I assume 1 atleast is excluded from the set of possible secret keys, since you can compromise the key just by looking at the equation if it is 1 $g^1 \mod p \equiv g$. In case g is less than $p$ ...
0
votes
2answers
62 views

Diffie-Hellman should size of group be a prime?

I have found some contradicting answers regarding finding a safe prime. When p is a "safe prime", this means that $(p−1)/2$ is also prime. We then define $q=(p−1)2$. In that situation, the order ...
0
votes
1answer
52 views

Encrypting a string of arbitrary size with a big integer

I am currently writing Python script that initiates a secure handshake. I am kind of reinventing the wheel here, so that I can properly learn it. Now, I have Diffie-Hellman mostly working from ...
0
votes
1answer
48 views

Diffie-Hellman what is the subgroup

I am trying to understand the safety precautions regarding the variables used in Diffie-Hellman and I was refered to this post answer Does the generator size matter in Diffie-Hellman?. In more ...
-1
votes
1answer
47 views

Diffie-Hellmann why bigger primes prefered over bigger pseudorandom secrets?

So I have build an application which purpose is to demonstrate Diffie-Hellman. I don't fully understand some of the arguments for the sizes of the numbers used in the algorithm. It seems like there is ...
1
vote
1answer
31 views

Diffie-Hellman server/client generated secret size

So I have implemented a client and a server performing Diffie-Hellmann, however sometimes the symmetric key is not valid? Example: Prime: 23 Primitive root: 5 client secret: 14 server secret: ...

1
2 3 4 5
16