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

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Obtaining Diffie-Hellman generator

In the Wikipedia article on Diffie-Hellman, the algorithm calls for a large prime modulus, $p$, and a generator, $g$, which is a primitive root of $p$. As far as my knowledge of number theory goes, ...
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How to encrypt a symmetric key with a shared secret?

I am reading this article (pdf) on the Diffie–Hellman key exchange. It states the following: At this point, the Diffie-Hellman operation could be considered complete. The shared secret is, after ...
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Understanding Diffie-Hellman - Choosing a bad g

I am taking a class on Cryptology, and I'm having a hard time understanding the potential pitfalls of Diffie-Hellman. Specifically, the professor gave the following problem: Alice and Bob want to ...
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How Diffie-Hellman authentication works? [duplicate]

There are a lot of good videos on a simple Diffie-Hellman in the internet but unfortunately that is susceptible to the MITM attack. I understand how with DH the two parties are able to calculate a ...
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Why do we need Diffie Hellman?

Diffie–Hellman offers secure key exchange only if sides are authenticated. For authentication, sides are using public/private key. So if side A knows the public key of the side B, then A can simply ...
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What are possible caveats when generating a group for use as parameters for Diffie-Hellman key exchange?

As reusing a widely used group for Diffie-Hellman key exchanges might lead to far easier third-party key discovery through precomputation for that specific group, I would like to know what can ...
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Why does a non-prime DH modulus creates a “NOBUS” backdoor

can't we do a nobus backdoor with DH modulus prime? Some have argued that with a prime modulus you can just get the order by doing p-1 and then factor it, thus it is easy to reverse. I argue that this ...
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How does a non-prime modulus for Diffie-Hellman allow for a backdoor?

Recently someone found that a Diffie-Hellman modulus used in a unix tool (socat) was not prime. This led some people to shout "backdoor". What I don't understand ...
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MiTM on RSA public key encryption

a) Alice just generated a new pair of public and private RSA keys (pkA , skA ) = ((N, e), d) and would like to start a private conversation with Bob. How can Alice interact with Bob and exchange a ...
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Extension of Diffie Hellman for many participants [duplicate]

How to do the Extension of Diffie Hellman Algorithm for Multiple Participants
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With OpenSSL and ECDHE, how to show the actual curve being used?

Using openssl s_client -host myserver.net -port 443 I can see the cipher negotiated is indeed using ECDHE for session key ...
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Degrade in performance with SSL_OP_SINGLE_ECDH_USE?

We have used SSL_OP_SINGLE_ECDH_USE when setting up our SSL_CTX . This seems to be causing a degrade in performance. I'm not able to find proper documentation for it except that it generates new ...
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history of non secret cryptograph

Prior to the discovery of any specific public-key schemes, such as RSA, an existence proof was developed whose purpose was to demonstrate that public-key encryption is possible in theory. Consider ...
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Forward Secrecy when using non-ephemeral DH

In context SSL/TLS, reading up on various sites, I find forward secrecy in DH key exchange being linked to its ephemeral use i.e. DHE. I don't fully understand this link, where does following ...
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Secure Key exchange using javacard applet

I am working on a javacard applet project where i need... Secure communication between two applets let say there is applet A and applet B. Let say both applet has their own RSA key pairs. Now I ...
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74 views

Non-numeric Diffie-Hellman?

It may seem that this is a programming question, but I just need advice on the cryptography side of the question. I want to implement the Diffie-Hellman key exchange algorithm on iOS (since no free ...
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Diffie-Hellman, RSA and the types of public key cryptography

Are these schemes fundamentally different? Are other schemes fundamentally different in the sense that you can do different operations with them (or the same operations, but needing different ...
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150 views

Session key Exchange, some doubt

I have to find a solution to this problem: I have a network composed by 1 server and some client. The server has a couple of keys (public and private) and it shares a secret key with each client. My ...
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Diffie-Hellman: choosing wrong generator “g” parameter and its implications of practical attacks

In traditional DH one chooses two shared parameters: a large prime "p" and base "g", which is primitive root mod "p". Suppose generation algorithm is broken and "g" generates only a subgroup (group ...
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What is difference between meet in the middle attack and man in the middle attack?

From my understanding man-in-the middle attack works as follow: Alice and Bob agreed to use Diffie-Hellman using $a$ and $q$. Alice sends $Y_A$. Before it reaches Bob, Charlie ...
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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 ...
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Which algorithm would be ideal for ephermal key generation followed by DH key exchange?

Bob and Alice, both generate a temporary public key pair each using X algorithm on their individual PC. After being authenticated by a third party, they use the DHE to come to get a common symmetric ...
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Counting points on elliptic curve over binary field

How to count number of rational points on elliptic curve over binary field?
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How is El Gamal different from Diffie Hellman Key Exchange [duplicate]

I am Reading RSA and Public-Key Cryptography by Mollin and I can't make out how El Gamal is different from Diffie Hellman Key Exchange. Any thoughts?
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Advantages using Diffie-Hellman or ElGamal

For what kind of usage should we prefer using Diffie-Hellman in order to exchange keys instead of ElGamal, and most important why should we use one or the other? I do not see a clear difference ...
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RSA & DH at risk due to math advances, will this eventually affect elliptic curves too?

I was looking into the predictions by some researchers that RSA and Diffie-Hellman may not be secure in the next few years due to advances in math and being able to calculate the discrete logarithm ...
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Why use Diffie-Hellman key exchange over RSA (or any public-key encryption)?

In Diffie-Hellman key agreement between Alice and Bob, Alice computes and sends $g^a$ to Bob, and Bob computes and sends $g^b$ to Alice. Alice then computes $(g^b)^a$, and Bob computes $(g^a)^b$; $g^{...
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Diffie-Hellman: *assumed* largest prime factor of order of $g$?

I've read in several places: some of my confusions about DDH assumption - comment by Thomas Pornin on his own post Is there a key length definition for DH or DHE? - the answer by Tom Leek that ...
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Decisional Diffie-Hellman: compute Legendre symbol of $g^{ab}$ from $g^a$ and $g^b$?

From https://en.wikipedia.org/wiki/Decisional_Diffie%E2%80%93Hellman_assumption: Importantly, the DDH assumption does not hold in the multiplicative group $\mathbb {Z} _{p}^{*}$, where $p$ is ...
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Generalization of the DL-assumption in bilinear group pair

When thinking about a pairing-based cryptographic scheme, I encountered the following problem. Let $e \colon G_1, G_2 \to G_T$ be a Type 3 pairing. Then: Given $P, zP \in G_1$ and $Q, zQ \in G_2$, ...
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Diffie-Hellman over several non-secured HTTP requests - will it work?

This problem is about setting up cryptographic keys on an IoT device. I don't want my devices to be set up with any cryptographic keys pre-baked, but actual communication have to be based on TLS. Now ...
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MITM Attack on Key Exchange Protocols

I was doing research on this attack and I am wondering, why is Diffie-Hellman always associated with such an attack? ​ Aren't other public key cryptography schemes vulnerable to the same kind of ...
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(Looking for reference) Variants of Diffie-Hellman

Sorry for asking a non-pure-crypto question but I think that crypto.SE might be the right place to find the right people to answer this: I remember having seen a few years ago, online and in HTML ...
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Why do $\alpha$ and the private key value in diffie-hellman should be from $2$ to $p-2$

I just started learning Diffie-Hellman Key Exchange. I couldn't get the reason of making $\alpha$ and private key for Alice and Bob constrained between $2$ and the prime number generated minus $2$ (=$...
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Do low-entropy fingerprints actually make any sense?

I'm thinking of ZRTP and OTR in particular here. From my understanding, after a Diffie-Hellman session is initiated, the shared secret is then hashed into a 4-digit number, which the two parties can ...
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Modular arithmetics in diffie-hellman

Studying the basics of Diffie-Hellman key exchange, I'm stuck at a basic operation used in the end of the key exchange (where you show that both computations actually are the same). Can someone ...
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Diffie-Hellman using a different modulus on both sides

For Diffie-Hellman Key Exchange, the used modulus is the same throughout the process. Is it possible to use 2 different for both sides? For example, $A \gets M^{d_1} \pmod{n_1} $ $B\gets M^{d_2} \...
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How does the size of the prime affect Elliptic Curve Bit Security?

I am using the MIRACL Library to implement an Elliptic Curve Diffie Hellman based Key Exchange according to ECDH-Scheme-Wikipedia. Referring to the Miracl Docs they suggest a few curves. Each curve ...
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Public Key Encryption using ECDHE and AES-GCM

Using a text book example, Alice and Bob want to communicate securely using encrypted messages over an insecure channel (the Internet). Alice and Bob have decided to use ECDH (using ephemeral keys ...
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Verifying Diffie–Hellman parameters someone else generated

I am auditing some software that includes compiled in Diffie–Hellman parameters (2048 bits). I can't be sure who generated the DH parameters or how they were generated. Question: Can DH ...
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What Diffie-Hellman parameters should I use?

After reading this article, I started wondering how should I approach the problem of choosing p and g params in 1024-bit Diffie-Hellman key exchange. In my project, I am going to establish keys ...
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How does Diffie–Hellman differ from elliptic curve Diffie–Hellman?

I didn't understand how ECDH actually works. Disclaimer: I know very little about elliptic curves. Here is how DH works: Alice and Bob agree on a prime number $P$ and a generator $G$. (They use one ...
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State level “Weak Diffie-Hellman” working for SRP too?

I've read about the "Weak Diffie-Hellman" attack (paper, website), where a resourceful entity like a state can pre-compute values for known primes to aid solving the discrete logarithm problem for ...
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267 views

ECDH or RSA more secure for symmetric key wrapping?

Suppose a message is encrypted with a symmetric block cipher with a random key. RSA is often used to wrap the symmetric key using the recipient's public key. In this case, the size of the message is ...
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729 views

Perfect Forward Secrecy with NaCl

I would like to use the NaCl cryptography library (or TweetNaCl), but I would very much like to have perfect forward secrecy for my application. From what I understand, all Bob needs to to decrypt a ...
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Security of SRP-6a against impersonating server choosing small/wrong N

I'm looking at an implementation of SRP (Secure Remote Password) that essentially follows the Stanford documentation (http://srp.stanford.edu/design.html). I'm worried about one aspect though: In the ...
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Is it possible to apply hill-climbing algorithm to Diffie–Hellman?

If Eve intercepts all the values communicated between Alice and Bob in a Diffie–Hellman key exchange, and applies the hill-climbing algorithm to reverse the modulo function, how will the algorithm ...
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Byte size of Diffie-Hellman public values

I have a scenario that uses RFC-3526's Diffie-Hellman Group 14 for 2048 bit key exchanges. From the document, it specifies the P (prime) value in hexadecimal value as: ...
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ephemeral-ephemeral ECDH and MITM attack [duplicate]

ephemeral-ephemeral ECDH is it susceptible to MITM attack ? if yes, can you please give me a detailed answer ( Workflow that can be followed by the attacker) and how we can prevent this attack (static-...
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How to exctract ECDH parameters from an OpenSSL-generated $G$?

I'm using ECDH for generating ECDH public parameters (p,a,b,G,n), I try to get this values using openssl ecparam -in cert.pem -text -noout For ...