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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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Where do the PKs come from in Bluetooth device?

I am studying the Elliptic Curve Diffie-Hellman (ECDH) on Bluetooth 4.2. There are some questions about the PK.. Where do these public and private keys come from? Who defines them? and Will it ...
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Encrypt using ECDH with two different EC public keys, minimizing payload size

Let's say Alice has the private EC keys $a$ and $b$, with a base point of prime order $G$. Alice computes the corresponding public keys $A = aG$ and $B = bG$, and sends them to Bob. Bob now wants to ...
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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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How does post quantum key exchange in OpenSSH 8 work?

OpenSSH 8 supports a post quantum KEX, namely sntrup4591761x25519-sha512@tinyssh.org It says in its description that it is basically NTRU + ECC X25519. However, I have tried but cannot understand how ...
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How many qbits are required to break Diffie-Hellman over a multiplicative group

There have been comparisons between RSA and ECDH with regards to the number of qbits (qubits) required to break the algorithm with a specific key size. But how many qbits are required to break "...
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Assuming the difference between success probabilities to be positive

Context: I am currently studying Theorem 3.1 in the paper Number-Theoretic Constructions of Efficient Pseudo-Random Functions by Naor and Reingold. The theorem basically states the randomized self-...
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Telegram VoIP key exchange

We've been trying to understand how Telegram's VoIP end-to-end encryption works. Key Exchange Detailed description of the key exchange algorithm is documented on the Telegram website. Here is the ...
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How to modify the Socialist Millionaire Protocol to be symmetric.

In the Socialist Millionaire Protocol, the roles of Alice and Bob are almost symmetric. By this I mean they do almost the same thing, until the very last step. In the final step, both parties check a ...
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Why does encryption in STS protocol protect against identity attacks?

The basic STS protocol contains encryption of the signature as shown in Wikipedia. https://en.wikipedia.org/wiki/Station-to-Station_protocol If we would like to defend against MITM attack, this ...
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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 to ...
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Key confirmation and other benefits of double ratchet

I'm trying to understand a comment from the Signal blog post Advanced cryptographic ratcheting. This article uses the term OTR ratchet to refer to a simple asymmetric DH ratchet, where Alice ...
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Precomputation attacks against ECDH

Diffie-Hellman groups are vulnerable to sieving precomputation attacks. These attacks allow a one-time computation against a given DH modulus that makes it practical to attack all subsequent key ...
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Reduction from integer factoring to computational Diffie Hellman

The computational Diffie Hellman (CDH) problem for ${\mathbb{Z}}^*_p$ is given a prime $p$, a generator $g$ of ${\mathbb{Z}}^*_p$, and a pair $(g^i, g^j)$ to compute $g^{ij}$. The value $g$ is called ...
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Is my way safe to remove SSL CA Cert by DHT and PoW NodeID for a decentralized system?

To implement a decentralized system, I wrote a TLS like P2P net stack. The main idea is removing CA Cert from the whole system by using a DHT for Naming and Key Exchange. I am not a crypto expert, so ...
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What ECDSA key is used to sign the ECDHE key exchange?

I have a server using TLS1.2 with an ECDSA certificate using secp256r1. The algorithms being used to connect to my browser are TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 as I expect from my server ...
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Are there any one-way operations that could be used for Diffie-Hellman post-quantum? (See criteria)

With quantum-computers looming, there is a need for Public Key Cryptosystems that can withstand attacks by quantum-computers. Are there any known one-way operations that fit the following criteria? ...
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Is Diffie-Hellman key exchange for multiple parties used in practice?

After reading this question about the possibility of using DH key exchange for multiple parties I went looking for a (C) library able to do this and found none. (I find it hard to believe there is no ...
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Plaintext DH keys in the message header in the Double Ratchet Algorithm

I've been reading details about the Double Ratchet algorithm, and I wanted some clarification regarding the aspect of the DH public keys going out in the plain in the header of every message. Quoting ...
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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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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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Is it possible to perform one-way Diffie-Hellman MITM?

Here's something that is bugging me recently: suppose that me and my friend establish an OTR session and - as a result of that - DH key exchange is performed. My friend verifies my key, but I cannot ...
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If 1 can be a random number in Diffie-Hellman Algorithm

I've done some calculations and Diffie-Hellman Algorithm worked for all chosen random numbers except $1$. In the description of the algorithm, I can't find information that the random number has to be ...
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How can I compute the theoretical total key-space for 521 bit elliptic curve ECDH private keys?

Assume a dumbed down RSA: the private hey is $3 \times 5 = 15$. $3$ and $5$ are the private key and $15$ is the public key. To brute force it, find the two prime factors of $15$ ($3$ and $5$). Is ...
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Reversing Diffie Hellman from the secret

This is a homework assignment that's been giving me some trouble: By eavesdropping on a Diffie-Hellman key exchange, we observe modulus $p$ the base $3$ $A\ =\ 3^a \bmod p\quad$ and $B\ =\ 3^b \...
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Which 'info' and 'salt' parameters to use in HKDF for TLS 1.3?

all the following discussion is for HKDF in TLS1.3: Regarding the 'salt' parameter in - HKDF-Extract(salt, IKM) as written in RFC 5869: HKDF without having to protect the secrecy of the salt. In ...
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Reason for including the public key of the key agreement in the KDF

I found the following text when looking up KDFs: In comparison, the so-called DHAES mode in IEEE 1363a mandates to use the binary representation of the sender’s public key as an input parameter. ...
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Multi-Party Offline Key Exchange Using Public and Private Keys

I hope the title already explains the problem I have in mind; but let me lay out some more details. Given public-private key pairs $P_A, P_B, P_C, ... P_Z$, (first $3$ of which are owned by our usual ...
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Securing MQTT communication

I am building kinda simple IoT project, but I would like to implement good security (just for educational purposes and fun). My plan is to build simple solution where one arduino board reads some data ...
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ECC Curve25519: How to generate this kind of private key? / Strange key exchange mechanism

I'm currently reverse engineering a program that uses Curve25519 key exchange in network communication. I have only a basic understanding of ECC, so maybe this thing just seems strange to me. The ...
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Complexity lower bound in Uber-Assumption family

I try to wrap my head around calculating of complexity lower bound using Corollary 1 from The Uber-Assumption Family by X.Boyen (http://www.academia.edu/download/30698012/...
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Key exchange during IKE_AUTH phase of IKEv2

This is what a casual IKEv2 handshake looks like : ...
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Algorithms to securely derive symmetric keys

I need to derive symmetric keys between two communication endpoints on an embedded device with 800MHz ARM core. What algorithms are available to have this secure key derivation mechanism? I know ...
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Is ECDH(E) Key Exchange FIPS 140-2 compliant?

We have read dozens of documents now - some that contradict each other - and cannot find a solid source of truth. Does FIPS 140-2 compliance allow for the use of elliptic curve cryptography as a key ...
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Diffie-Hellman combined with DSA/RSA

we have learned Diffie-Hellman, RSA and DSA (Digital Signature Algorithm) in university. Because DH is vulnerable of Man-in-the-Middle we had the task to program the DH combined with RSA to protect ...
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Solving discrete logarithm when p is not a safe prime

If you have the cyclic group of integers modulo $p$, where $p$ is not a safe prime, as well as a generator $g$ with which for all factors $q$ of $(p-1)$, $g^{(p-1)/q} \ne 1$, This answer says that ...
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My attempt of combining socialist millionaire and Diffie-Hellman. Is it any good?

I've come up with an algorithm to solve the socialist millionaire problem, but I'm not sure if the algorithm is secure. I wasn't able to find any flaw in it, but it seems too simple to be secure, so I'...
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Is it possible to modify SSL handshakes to enable PFS while still using RSA during the handshake?

I know we could possibly be using DH key exchange, that would enable PFS. However, what if we make modifications on our SSL 3.0 handshake such that the only cipher we use is RSA for the achieving PFS? ...
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Best group if one wants the discrete log problem to be hard?

Suppose one is implementing a cryptographic scheme over a group where one needs the discrete logarithm to be hard - what is the recommended group to use? I'm looking for a group where calculations are ...
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Help to understand the KDM in SP800-56A, and the usage of “FixedInfo”

Can somebody help me to understand the LOGIC behind Key-Derivation Methods (SP800 56A CH5.8)? This is my common understanding and please correct me if any wrong.. Alice and Bob can general individual ...
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Prove that a signature scheme is RUF-NMA and not EUF-CMA

I am working on the following exercise: Now, assume the following signature scheme: $\operatorname{KeyGen} (1^k$) : On input of a security parameter $k$, choose a symmetric bilinear group with ...
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What are some potential applications of trilinear mappings?

In "Applications of Multilinear Forms to Cryptography" Boneh and Silverberg give "one-round n-way Diffie-Hellman key exchange protocol" as a potential application of n-multilinear mappings. If we ...
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Is RSA in decline across the board?

From what I gather from the internet (source), the recommended practice for 2019 and beyond is to avoid RSA and use ECDH and ECDSA. Is this the general case?
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Most energy-efficient authentication protocol?

I am looking for a cryptographic protocol that is as energy-efficient as possible. I am talking about battery drain. Alice wants to do a mutual authentication with Bob. Maybe symmetric is good, maybe ...
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How to decrypt plain text x using man in the middle attack

Suppose Alice want to share a plain text $x = 5$ to Bob; using RSA, DHKE, and El-Gamal. My question is if Man-in-the-middle attack is applied then weather oscar can compute/decrypt plain text in all ...
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Burmester Desmedt confused on the last step

I try to implement in code the traditional burmester desmedt algorithm for group key agreement: But I have the following question regarding the last step: $K=k_{i-1}^{nx_i}K_i^{n-1}K_i+1^{n-2}\dots ...
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Sharing secret content with multiple recipients

I have a sender and N recipients, and am thinking of using the following scheme to send secret content to those recipients. This is similar context to a group chat or email. I am no expert in crypto ...
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Simple but secure method to share secret (128 bit AES key) though an untrusted relay

I am creating an end-to-end encrypted group messenger, and am looking for a way for online members of the chat to a arrive at a shared secret that can be used as a cryptographic key. This will ...
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186 views

Parameters and key dimension for DH and RSA

I studied RSA and Diffie-Hellman key exchange from a quite old book (Discrete Mathematics by Berardi, Beutelspacher) and so I wonder if the recommended dimensions for the prime p and the secret ...
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Found weil pairing. Index Calculus method on the results of weil pairing

Consider Elliptic curve with p = 59, A = 1, B= 0, P = (25,30) and Q=(35,31). So I tried to solve this using MOV attack. The torsion point for them E[5] is R(-25,30i) where is sqroot -1 Chosen two ...
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Property of Multiplicative group of integers mod n

While practising on paper I've realized of a property of multiplicative group of integers mod $n$. First, let's define $G$ being $p$ a prime and $g$ a primitive root mod n or a generator of a ...