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

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Security equivalent to Diffie–Hellman problem?

I've been doing the security proof for one of my Theorem. Basically, given $g^a$, $g^b$, $g^{cb}$, $g$ and $c$ as known values. Is the problem of computing $g^{acb^{-1}}$ equivalent to the Diffie ...
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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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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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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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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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Can we reduce Diffie-Hellman problem to “Discrete-log inversion” problem?

Let $G$ be a cyclic multiplicative group of order $n$. Let $g$ be a (public) generator of $G$. The Diffie-Hellman (DH) problem asks: Given $g^x, g^y\in G$ for $x, y\in \mathbb{Z}^*_n$, to compute ...
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Diffie–Hellman Ephemerality Nomenclature

Below is a short excerpt of available DH cipher suites available on a machine. I understand EDH is ephemeral DH, and that ECDH is for Elliptic-Curve DH which is computationally faster. ECDHE is both ...
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Does there exist a two-pass AKE protocol that is secure in eCK model and also has PFS?

As we can know that the best two-pass AKE protocols with DH message can achieve is the weak form of perfect forward security (wPFS) which guarantees security against the passive adversary. But ...
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Potential vulnerability in DH key selection - am I understanding this right?

I'm reading through a DH implementation, and I think I found a potential hole. Public $p$ and $g$ values are properly selected. A candidate secret value $\bar a$ is pseudo-randomly selected such ...
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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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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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RFC 3526 - What does pi mean?

In RFC 3526 there are a series of primes listed as standard parameters used for Diffie-Helman. The primes are list in two formats. One is the long format, where the number is given in hex. For ...
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303 views

Which is better ECDHE with TLS 1.0

I have a webserver which only supports TLS 1.0 and I am not sure about something: Which is the better cipher in this group when aiming for the best security? ...
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Diffie-Hellman for Encryption

In learning how DH works for cryptography applications, I'm coming across some confusing language. For starters, most of the time DH is discussed in the context of "generating" their shared secret. ...
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Stream cipher with Diffie-Hellman and Cryptographic Hash Function? [duplicate]

I know: Never do your own crypto. But this question is just theoretical. Assume you do a Diffie-Hellman Key Exchange with a server to produce a shared secret $x$. Then use a cryptographic hash ...
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How do I generate a session key using the Diffie Hellman algorithm?

How to generate a session key between two nodes in two different subnets when the nodes don't know each other directly, using diffie hellman algorithm?
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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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Is simple XOR with secret key using DHE secure?

Client and server have given generator 3 and modulus which is 256 bit prime same all the time for all clients and server (simply hardcoded). They both generate a private exponent and send result to ...
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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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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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Security Level Estimate when Cascading/Compositing Ciphers?

Way back when, DES had a theoretical security level 56-bits. 2-key TDEA provides about 80-bits of security, and 3-key TDEA provides about 112-bits of security. Obviously, those security levels are not ...
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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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Chosen ciphertext insecurity in an ElGamal variant

I'm trying to prove something and if I can show that there is a simple way to calculate $(g^a \bmod p)^k$ if I know both $g^k \bmod p$ and $g^a \bmod p$, then (I think) it will help me prove it, but ...
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Generalizing the conversion of Diffie-Hellman to El Gamal

How can we generalize the conversion of Diffie-Hellman to El Gamal public-key encryption scheme? The goals is to be eventually able to show that any 2-round key-exchange protocol can be converted into ...
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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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Do ECDH and ECDSA combined solution provide an authenticated protocol exchange solution in MCU environment?

I'm working on a project in MCU (micro controller) environment with GPRS connection to exchange data securely with the cloud. The encryption algorithm has been selected to use AES. I did some search ...
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ECC - ElGamal with Montgomery or Edwards type curves (curve25519, ed25519) - possible?

I know the usual way of using getting shared secrets for encryption with ECC is DH, however, this only works with two keypairs of exactly the same kind, for example two curve25519- or two ...
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Derive a public EC key from two public EC keys

Alice has two EC key pairs: $a_1$, $a_2$ are private keys (integers), $A_1$, $A_2$ are the corresponding public keys (points). Alice and Bob want to create a new public key $C$. Alice must prove that ...
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Is there a field guide to ECC for the IT Security layman?

I'm trying to understand ECC from an IT layman's perspective and am trying to separate the theory from the standards, and understand why certain features are implemented or not implemented in the ...
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537 views

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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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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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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Relations between RSA and DLOG, factoring and DLOG

Definition: (The generalized Diffie-Hellman problem) Let $n=pq$ for two large primes $p,q$. Given $x, x^a, x^b,n$, find $x^{ab}\pmod{n}$. (1) Is there a known reduction from the GDH problem ...
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How does $g$ being a generator imply Diffie-Hellman's correctness?

In the Diffie-Hellman protocol for key exchange over an unsecured channel, we choose $p$ and $g$, where $g$ is a generator of $\mathbf{Z}_p^*$. However I want to know why this assumption makes the ...
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Perfect Forward Secrecy in TLS

I read that TLS does PFS using Diffie Hellman. However, DH can be used even without certificates - so how is DHE-RSA better than plain DHE? Is DHE a insecure algorithm, that DHE-RSA is needed?
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How to find generator $g$ in a cyclic group?

As generator $g$ is use in DH how to find combination of prime $p$ and $g$? eg: if we choose $p=23$ its generator is $7$ (given in book) how to find it?
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Diffie-Hellman is Post-quantum secured?

If Alice and bob have a secure channel for key-exchange and mallory don't man-in-the-middle attack them but in the future eavesdrop connection and see the key exchanged, can mallory break it like RSA ...
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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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At what stage is DHE and RSA used during the SSL/TLS handshake?

At what stage of the SSL/TLS handshake is the DHE and RSA used and what is the purpose of using a pre-master secret when you could just use RSA to exchange the symmetric key (i.e. AES) for further ...
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Is EKE attackable by a brute-force password search?

So I'm trying to properly implement the EKE protocol and I'm using C# with the Windows CNG and ECDH key exchange. I need to use this because it's FIPS certified and all that jazz. So what I'm ...
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In the STS Authentication Protocol, why are the signatures encrypted?

From Wikipedia: (1) Alice → Bob : g^x (2) Alice ← Bob : g^y, E_K(S_B(g^y, g^x)) (3) Alice → Bob : E_K(S_A(g^x, g^y)) I know there should be something I'm ...
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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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Diffie-Hellman secret key choices

I'm trying to understand why the secret keys used by Alice and Bob in Diffie-Hellman are $a,b ∈ ℤ∗p$. Say $a$ is $p - 1$, wouldn't the transmitted $g^a$ be 1 mod $p$ by $FLT$? Now anytime a ...
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Why is diffie-hellmangroup1-sha1 used instead of diffie-hellman?

For SSH why is diffie-hellmangroup1-sha1 used instead of just diffie-hellman? In other words, why is the hash function used?
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Can a EC private key be derived from a public key?

I understand that the public key does not expose the private key. That is not the question. The question is: Given a EC public key, can a different, but plausible and functional private key be ...
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Is there a point using GCM block chiper with Authenticated DH?

I'm delivering shared secret with DH exchange, using a static key for signing and an ephemeral for session, so is there a point using GCM for encrypting the data, or is a simple CBC/CTR block cipher ...
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How can I show that the DDH problem is self-reducible?

I have trouble to understand how I can show that the Decisional Diffie-Hellman problem (DDH) is self-reducible. I found this as a description of a random self-reducible problem. ...
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How well does breaking multiple DH key exchanges over the same group scale?

Suppose you are running a server with the Diffie-Hellman parameters (so the group G and generator g) generated once. There are ...
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How large should a Diffie-Hellman p be if the messages are encrypted?

How large should the prime $p$ and generator $g$ values be in a Diffie-Hellman handshake if the messages are encrypted. If the key that encrypted the Diffie-Hellman messages becomes compromised, ...
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What's the strategy for future directions in cryptography? Bigger numbers/faster searching, or new methods, say, of factoring?

I'm taking a course in cryptography, and I would value any comments. This is not too technical a question, but more about directions or strategy in cryptography. My question is, is public key ...