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

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What is the starting point of Hellman's TMTO method?

I understand what is happening and how the endpoint is computed but I'm still a bit unsure of where "SP" (Staring Point) came from. Are the starting points, randomly selected keys from the key-space ...
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How does the Number Field Sieve find the target number for Diffie-Hellman?

I have read some papers relating to the Number Field Sieve, but I could not figure out how this algorithm helps in Logjam, or even what is meant by the number field. What is this? What is meant by ...
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About random self-reducibility of DDH

In Section 8 of this, Lindell presents a construction of an oblivious transfer protocol which is secure in the malicious model under the following variant of the DDH assumption (page 53): [F]or ...
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Man-in-the-middle-Attack three Parties [duplicate]

How does this work in Diffie Hellman ? I'm working for days on this but i'm a little bit Confused. If Oscar changes only the last key (for example Kabc ) is this enough ?
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NIST Diffie-Hellman prime: how was it picked? Where did it come from?

According to this Matasano Crypto challenge, the NIST "likes" the following prime modulus, which appears to be expressed in hexadecimal: ...
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Creating ECDH using OpenSSL

For academic reasons, I'm playing around with OpennSSL 1.0.2g. I tested RSA encryption/decryption. I created key exchange with DHKE. But I'm struggling to find a way, to create ECDH, using only ...
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how a MITM attack works against tripartite in DH? [closed]

Must Oscar change only the Key $K_{abc}$ (Alice, Bob and Charlie) or does he have one key for everyone of them ?
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Is Schannel supposed to use SHA1 for (EC)DHE params?

I captured a TLS 1.2 handshake on my server (WIN2012.R2/IIS 8.5) and noticed that SHA1 is being used to hash ECDHE parameters despite both the server and client(s) supporting SHA2 signatures. ...
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How large should a Diffie-Hellman p be?

In a Diffie-Hellman exchange, the parties need to agree on a prime p and a base g in order to continue. Assuming some ...
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64 views

Diffie-Hellman: Calculating the private key from the public key with Java

I have the task to calculate the private key from the given public key and have the hint that the secret exponent lies in the range from $-2^{31} < e < 2^{31}$. To find the exponent I ...
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Verilog simulation & synthesis of Diffie-Hellman key exchange

Is there any freely available verilog implementaion of Diffie-Hellman key exchange? I couldn't find anything using google. So, assuming its not there I started implementing on my own. The code is ...
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What info should be signed with a digital signature to provide entity authenticaton for DH?

$i \to r\colon\; g^x\bmod p$ $r \to i\colon\; g^y, \langle g^y,g^x\rangle_r$ $i \to r\colon\; \langle g^x,g^y\rangle_i$ Looking at run 2, I am trying to work out why it is necessary to include ...
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If we should not reuse primes in DH, shouldn't we not reuse ECDH elliptic curve properties?

An article How is NSA breaking so much crypto? describes NSA's methods for breaking encryption. If a client and server are speaking Diffie-Hellman, they first need to agree on a large prime number ...
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84 views

Elgamal with secret key equal to zero possible?

From various sources (e.g. this paper, page 3), the key generation algorithm of Elgamal samples the secret key $x$ from $\mathbb{Z}_q$, which is identifiable to $\{0, 1, 2, \dots, q-1\}$. My ...
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139 views

The difficulty of computing discrete logs

I understand that in Diffie-Hellman it should be hard to compute $a$ given $g$ and $g^a$. In computational Diffie-Hellman, it appears to be hard to compute $(g^{ab})$ from $g^a$ and $g^b$. As for ...
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103 views

Understanding Hellman's TMTO

I am trying to understand the basic TMTO by Diffie Hellman as described here. I am having trouble understanding this passage here: Hellman had the idea of storing the dictionary in the form of ...
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TLS/SSL's usage of Non-Ephemeral DH vs DHE

These questions revolve around DH and ECDH vs DHE and ECDHE. Specifically within the context of TLS/SSL. There are three ...
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359 views

Small subgroup confinement attack on Diffie-Hellman

I am trying to understand the small subgroup confinement attack on the Diffie-Hellman algorithm. I will present the attack and try to explain why it works. Small subgroup confinement attack on the ...
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343 views

Why is “multiplying” $g^x$ and $g^y$ not possible?

The computational Diffie-Hellman problem states that for a cyclic group $G$ of order $p$ and a generator $g$, it is hard to find the value $g^{xy}$ given only $g^x$ and $g^y$ (but easy if either $x$ ...
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AES encryption using a Diffie-Hellman key exchange

I have two systems which need to encrypt their communication by AES-128. The key for the AES encryption should be exchanged with the Diffie-Hellman (DH) algorithm. Now, I've read about DH and got a ...
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Is this Diffie-Hellman key exchange variant vulnerable to man-in-the-middle attacks?

As we all know, the Diffie-Hellman key exchange protocol without authentication is vulnerable to a man-in-the-middle attack. And if we use STS(Station-to-Station protocol) instead, it would be secure. ...
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Why does the modulus of Diffie–Hellman need to be a prime?

I read a lot about Diffie-Hellman, but there is one thing I dont understand: why does the modulus p need to be a prime? What if it would not be a prime?
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Can (EC)DH keys be used as the signed content in X.509 certificates?

From Wikipedia's article on ECDH: The public keys are either static (and trusted, say via a certificate)… Also see this question on this very site. These indicate to me that a certificate ...
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Certificateless cryptography Implementation

Hello guys I am trying to implement Certificateless Cryptography algorithm with reference to this base paper. Right now I am trying to implement the code in java. ...
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One-time pad using RSA and Diffie-Hellman functions

Suppose that Alice and Bob use an encryption algorithm based on a one-way function $F$ (Eve knows it), and $r$, a secret key shared between Alice and Bob (Eve doesn't know it). Key is computed as: $K ...
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ECDSA vs ECIES vs ECDH

Recently I started studying Elliptic Curve Cryptography and I just loved it. I want to transfer some big data (like 3KB), What is the best method, ECDSA, ECIES, or ECDH (and why)? I am confused, how ...
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How to perform decryption in this single-bit PKE scheme?

Consider a cyclic group $G$ of order $q$, and let $g$ be a generator for $G$. Assume $(G, q, g)$ is public. Consider the following 1-bit public-key encryption scheme. To $generate (pk,sk)$: $x ...
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59 views

Small subgroup attack on Diffie-Hellman key exchange

Alice and Bob are using DHKE in the group $\mathbb{Z}_p^ * $, where $p = 1031 = 2 \cdot 5 \cdot 103 + 1$. Their generator $g = 2$, which generates a multiplicative group of order $515$ in ...
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39 views

Security of Diffie Hellman in specific cyclic group

For some $k$, let's say $p = 1+ \prod_{j=1}^k q( j)$, where $q(1)=2$, $q(2)=3$, if $p$ is prime, the diffie-hellman key exchange is not secure in cyclic group $Z^*_p$. Why?
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27 views

how MitM compute server secret number in logjam

I would like to know how man in the middle can compute the server secret number if the prime is 512 bit in length and if knowing ($g$) parameter as in the following figure help him or not? is the man ...
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44 views

what is DHE_EXPORT cipher suite

I need to know what is exactly DHE_EXPORT cipher suite and why it is still supported by some servers. Is there any implementation or details about this weak crypto?
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50 views

Proper forward secrecy [closed]

Currently I have a protocol using a simple RSA to AES handshake. I have been reading more and more and would like to implement proper forward secrecy, but at the same time I'd like to improve the ...
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Selective and existential unforgability of signature schemes

I understand that one can define EUF-CMA of a signature scheme is terms of a game where the adversary is allowed to query signatures on messages of his choosing, and at the end of the game he must ...
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RSA_DH vs ECDH implementation

In ECDH protocol is possible, naturally, to use the same algorithm for calculate a secret key for both communication parties (Alice and Bob for example). It is possible to design also a same algorithm ...
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73 views

Are developers expected to implement Diffie-Hellman key exchange themselves?

I noticed that the GO standard library has some really nice functions for performing AES encryption / decryption in various modes. However, I couldn't (yet) find anything for Diffie-Hellman key ...
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How to compute the discrete logarithm of Diffie-Hellman with a composite modulus?

Imagine $n = pq$ with $p-1 = 2 p_1 p_2$ and $q-1 = 2 q_1 q_2$. I can compute the discrete logarithm of $y = g^x \pmod{n}$ by computing the discrete logarithm of $y$ modulo $p$ and $q$. But then how ...
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Supersingular Isogeny Key Exchange broken?

Found this report detailing a quantum algorithm for computing isogenies between supersingular elliptic curves. http://cacr.uwaterloo.ca/techreports/2014/cacr2014-24.pdf with the quote ...
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Where did Martin Hellman acknowledge Ralph Merkle's contribution to public-key cryptography?

I am trying to find the article to reference when discussing the Diffie-Hellman key exchange. According to Wikipedia Hellman said that The system...has since become known as Diffie–Hellman key ...
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Why do the subexponential algoriths for the DLP not work for the ECDLP?

Elliptic curve cryptography is much more secure for the same parameters because attacks that work on the DLP do not work on the ECDLP. Why do the attacks fail in the latter case?
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Step by step conceptual implementation of AUTHENTICATED Diffie-Hellman?

I'm already doing classic DH with pre-shared key in my setup, and it prevents people knowing the same password from eavesdropping on others' traffic. But it doesn't cover situations where a third ...
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How do we calculate DHKey using A's public key and B's private key?

I have 2 set of public/private keys. I would like to know how I can calculate DHKey. e.g: ...
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66 views

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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65 views

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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1answer
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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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351 views

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 ...