Questions tagged [diffie-hellman]

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

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Static Diffie-Hellman in TLS

Static Diffie-Hellman (cipher suites with DH in their name but neither DHE or DH_anon - ...
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Other than an exponent greater than 1, what are the considerations when creating a random 256-bit private key using Diffie Hellman?

Let's assume that I choose the bits for my 256-bit private key exponent by flipping a coin 256 times. Are there any other issues, besides the randomness of the 256-bit private key to consider? For ...
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Alternate to distributing master key to every user in circle of trust

I am designing an end-to-end encrypted file storage system where only the user should be able to access their own data. The best I could come up with is a system designed around a master key that is ...
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Replacing elliptic curve diffie-hellman primitive with elliptic curve cofactor diffie-hellman for specifc curves?

From what I've read about elliptic curve Diffie-hellman with and without cofactor (I am pretty new to the whole thing so I am not able to understand everything) is that when the cofactor of the curve $...
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How is the recommended NIST modulus for DLP chosen/calculated?

NIST recommends a 256-bit private key exponent for DLP with a 3072-bit modulus. From this answer it appears that the range of private key numbers is derived by calculating a prime modulus via $2⋅p$ ...
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How does ECDHE fit with AES and SHA?

Hi I'm trying to piece together how AES, ECDHE, and SHA all work together. From what I understand ECDHE is uses asymmetric cryptography to generate a shared key from a public and private key which 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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Diffie-Hellman Primitives in SP800-56A

I wonder if someone can give an explain about the different between two Diffie-Hellman Primitives defined in SP800-56A, CH5.7.1 5.7.1.1 Finite Field Cryptography Diffie-Hellman (FFC DH) Primitive 5.7....
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Invalid curve attack: finding low order points

Background Here's a description of page 182 of "Guide to Elliptic Curve Cryptography" by Hankerson, Menezes and Vanstone. Here's a quote from that page: The main observation in invalid-curve ...
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Shared secret beginning with 0h?

I'm designing a system where my hardware piece uses an ATECC608A to calculate an ECDH shared secret in order to exchange data with a HSM in the cloud. For some unknown reason, whenever the first ...
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51 views

DH prime size required to force an attack of $2^N$ steps

Why the size of a DH prime $p$ should be about 6800 bits long to force an attacker to perform $2^{128}$ steps to attack the system? How is this relationship 6800-128 established?
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How to Formalize Noise Protocol Messages

I try to understand the messages of the Noise Protocol Framework. The handshakes are based on Diffie-Hellmann key exchange. This is an example for a handshake pattern: ...
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What is the actual result of a Logjam's DH attack?

Does a Logjam attack calculate a group of probable Diffie-Hellman private keys for a user and then try them one at a time to see if it can decrypt the message - or does it directly calculate the one ...
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Purpose of key evolution?

When generating and exchanging keys, what is the purpose of performing key evolution after public key exchange + authenticated encryption?
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45 views

Diffie-Hellman and secret key size

How can one guarantee that the generated DH secret key is of certain length? Say 256bit. Actually, prime length is not enough since the remainder of the last process, the modulus, may result in too ...
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Could Diffie-Hellman protocol serve as a zero-knowledge proof of knowledge of discrete logarithm?

The Schnorr identification protocol is widely recognized as the simplest ZKPoK of the discrete logarithm (more clearly, Honest-Verifier ZKPoK). However, I can't figure out why this simple protocol, ...
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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 to exchange a common key to a group of person using Elliptic-curve Diffie–Hellman (ECDH)? [duplicate]

In ECDH, when two persons want to share private keys, they first select a point $G$ on the elliptic curve and after that, each of them picks a random integer $a$ and $b$, respectively, and multiply ...
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How to find at least one private key from a large list of compressed public keys secp256k1

Not long ago I saw a discussion on the Bitcoin Talk forum: https://bitcointalk.org/index.php?topic=5060735.msg50736695#msg50736695 Please give advice and working methods? Is it possible to find at ...
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Can I do a forward secure half-round ephemeral-static ECDH?

In the context of the project we are working on recently, we would like to enable users to "leave a message" to someone on the Internet securely. Our setting is as below: ECC key pairs for open ID ...
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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 does the key agreement process take place in Virgil E3Kit SDK for end to end encryption?

I'm using Virgil E3Kit SDK to implement end-to-end encryption in my App. Their E3Kit SDK is very effective and not too hard to understand, but I still don't understand how does the key agreement ...
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What key is used to encrypt the certificate and certificate verify message in TLS1.3?

Which key is used to encrypt certificate and certificate verify message in TLS1.3? I could not figure out which one it is reading section 4.4.2 of RFC 8846 and I only saw a vague mention on page 11.
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What SALT value will be used in HKDF_EXTRACT in TLS1.3?

What SALT value will be used in HKDF_EXTRACT while generating the Handshake Secret (when there will not be any PSK)?
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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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How to multiply two Public Keys in Elliptic Curve in Go

I am working on a messaging client similar to Signal. I am stuck on implementing Tripartite Diffie-Hellman handshake in which three DH exchanges are combined to authenticate both parties and produce ...
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42 views

Why public key has two parts in my secure messaging client similar to signal

I am working on a Golang code similar to Signal protocol. I need to modify it. I am confused on tripartite Diffie-Hellman handshake part of code, i.e. why public key has two separate parts as compared ...
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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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Using Diffie-Hellman secret key to encrypt/decrypt data?

My end goal is to encrypt data with AES-128, send it to other process and decrypt it there. While using DH key exchange protocol. I have used DH to generate a 256 bytes shared secret, but I can't use ...
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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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In Diffie-Hellman, are $g$ and $p$ universal constants or are they chosen by one party according to a set of rules?

I can't find any clarity on this. In textbooks, what I'm reading suggests there's already a standardized $g$ and $p$ that everyone uses, but I can't find what they are. The closest I've come to is ...
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How should one refer to the smallest remainders generated by a modulus within DH or DLP?

It's my understanding that the integer base and exponents chosen to create the initial public keys in DH are from the remainders of a modulus. For example, if the value of the modulus is $N=11$, a ...
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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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Diffie-Hellman: Recommendation of the base size?

Based upon choosing a prime $p$ of recommended length and $N=2p+1$, where $N$ is also prime, and $a^2$ is not congruent to $1 \pmod N$, and $a^p ≡ 1 \pmod N$, I believe you can rely upon $a$ as having ...
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Can Shamir’s Trick crack the cryptographic strength of ECDSA?

Recently stumbled upon a discussion in the forum What is Shamir’s Trick used for? Are there any such examples?
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If DDH is hard then CCA-secure PKES exist?

My cryptography slides describe several relations between cryptographic problems. I don't still have a good justification on the following: If decisional Diffie-Hellman problem is hard then there ...
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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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Signal protocol: when, and why, is X3DH run again between the same two users?

This question concerns the Signal protocol's X3DH key agreement protocol as documented here. Obviously, if Alice and Bob have never contacted each other before, they need to run X3DH at least once to ...
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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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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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Equivalence of cryptographic problems

Are integer factorization, discrete log and ECDH problems equivalent? I know that factorization and discrete log are equivalent but are one of those two problem equivalent with ECDH? Cand someone ...
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In NIST modulus and key size recommendations is `group` equivalent to modulus and `key` equivalent to exponent?

Looking at the following NIST recommendations for a discrete logarithm, for 2016-2030 and beyond they list 3072-bit number for the group and 256-bit for the ...
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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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239 views

Diffie-Hellman private key recover with non-prime modulus

Say we have a classic Diffie-Hellman key exchange. We have the following parameters of a public key: p,g,y Where $p$ is the modulus, $g$ is the base, $y$ is the ...
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Is it safe to send IV in plain text for every request?

Currently, I am creating a project with an IoT device. This is an offline device which shows a QR code which can be scanned by a mobile device, which sends this code to a server. The server handles ...
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Brute force against custom algorithm [closed]

In my free time, I write an algorithm for fun (and it may be the best hobby I had so far). Currently, the output this algorithm produces is indistinguishable. I ran multiple analysis process and ...
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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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What happens if we choose the random secret keys in Diffie-Hellman greater than prime?

Diffie-Hellman works as follows: Given public parameters $p$ (a large prime) and $g$ (always referred to as a generator of $(\mathbb{Z}^∗_p)$. Then: Alice randomly chooses $a<p$ and sends $A\...
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What should I use for consequent AES key derivation?

I am writing a small chat program to explore some methods and concepts in cryptography and currently I am using a shared AES key tunneled with RSA which upon further reading revealed many flaws both ...
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What motivated the creation of RSA and ECDH?

Recently I've been learning about cryptography and so far I am loving it. However, there are some things I do not comprehend. As far as I know, RSA was published in 1979 while New Directions on ...