Questions tagged [key-exchange]

Key exchange protocols allow two parties to produce a secret session key over a public channel.

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Diffie Hellman protocol connect to DES [closed]

I have working Diffie Hellman protocol, it works fine on ports and randomly generated P, G, A. And I need to connect DES key to this Secret Key from DH. My DES file works like this: Type name of the ...
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Curve25519 Key Validation

According to the original paper of Bernstein, there is no key validation needed when using Curve25519 for Diffie-Hellman Key Exchange. However, where does this property come from? Is there any proof ...
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How to exchange keys despite a MITM, using some short known password?

The simple scenario is two devices on one WiFi network sitting side by side. The user can copy a short code from one device to the other to be the "password" however this code can't be too ...
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Diffie-Hellman and identify with certificates

alice and bob use the Hellman-diffie protocol to exchange keys and identify each other with certificates, signed by a trusted certifier (CA) and each has a private key that matches the public seducer ...
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How to sign messages using the NOISE Protocol Framework?

I wanted to learn more about secure messaging and started a personal project using the libhydrogen library. From my understanding, instead of using public-key ...
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ECDH/ECDSA key exchange on embedded devices

Two devices are communicating only with each other and shall do this with AES encryption. Both devices are offline, have very limited storage and use a small cryptographic coprocessor which is able to ...
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MAC-then-encrypt in SIGMA protocol for authenticated key exchange

The SIGMA protocol proposed in 2003 and used in TLS 1.3 and IKE stands for "SIGn-and-MAc" and can optionally protect identity using encryption. The SIGMA-I variant illustrated below ...
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Post-quantum asymmetric encryption algorithms

One could use Falcon-512 for establishing a private and public key for an asymmetric context. Whereas in a symmetric context, we could use firesaber/saber/variants in order to obtain a shared secret ...
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Key storage management of session keys and long term keys

In key management, one of the topics is key storage, I want to know where and how these keys(long-term and short-term) are stored? For example I read that android password apps use KeyStore api to ...
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Symmetric Exchange Key Sharing

Question: Suppose that there are 10000 = 10^4 banks and 10 payment card organisations (PCOs). How many secret keys will be needed if each PCO shares a unique secret key with each bank? How many extra ...
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Is this variant of Diffie-Hellman viable and quantum resilient?

In this paper the author suggests using a variant of Diffie-Hellman which involves floating-point numbers of arbitrary size in the generation of a shared secret. There are no primes, calculations are ...
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Securely transmit signed token (e.g., JWT) over insecure channel

Apologies if this is already answered somewhere, but I could not find it. I have a setup where a client has a JWT (RSA- or ECDSA-signed), and needs to prove that fact to the peer which issued the ...
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Why is this not a viable key exchange algorithm? [duplicate]

I was just wondering why this kind of algorithm can't be used instead of, say, Diffie-Hellman to exchange keys: Alice decides on a key she wishes to share with Bob. Alice generates a stream of bytes ...
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Rounding function used in Saber Key Exchange

In Saber: Module-LWR based key exchange, the authors use a rounding function called $\textit{bits}$, defined (in page 3) as follows: $bits(x, i, j)$, with $j \leq i$, gives $j$ consecutive bits of a ...
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TLS 1.2 Server Key Exchange problem

Below the Wireshark snapshot of the handshake compliant to the TLS 1.2. The position 1 displays the enum ServerECDHParams where I can use any curve having the own ID RFC8422. I'm free for example to ...
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Can TLS be used simply to exchange keys using the handshake protocol?

From what I understand, in general, TLS consists of two protocols: 1 - Handshake protocol: uses public-key cryptography (ECDH, DH) to establish a shared secret between the client and server. 2 - ...
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Security Proof, Sequence of games and birthday paradox

The sequence of games security proof approach is very confusing. For example, I am trying to understand it in the following paper https://www.dropbox.com/s/dhsgsognxviwacv/Provably%20Secure%...
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Can Key-Encryption Key (KEK) be symmetric?

This from Cryptography course from Coursera: Key wrapping or encapsulation using a KEK can be accomplished using either symmetric or asymmetric cipher For my information KEK solves the key ...
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If P256 ECDH shared secret contains ~128 bits of security, does using first half of the secret (= 128 bits) contain only 64 bits of security?

There's this rather popular open source project (I'd rather not name it before possible responsible disclosure) that computes a P256 ECDH shared secret (256 bits) and uses only first half of it, rams ...
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How to securely share AES key between two remote devices (client and server) through UDP protocol?

I have two separate system (client) and (server). I am having a problem which is to encrypt a message from the client and decrypt at the server. In order to do that, I am required to transmit my key ...
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How to generate the exact AES key in both client and server side?

I am using AES to create a secure tunnel for transmission of data. As the symmetric key encryption will require the same key to encrypt and decrypt, so we need to generate the exact same key for the ...
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Is there an implemented Id-based key exchange protocol?

I need to use some kind of authentication of the client during my key exchange process. During my research, in this article I learned about identity-based key exchange and authentication, and I was ...
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Decryption : How to secure the Key in offline mode [closed]

I am new to cryptography. I have a package to be shared with Bob which is something like below: Package contains: data.zip and Application where, data.zip is ...
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The title of the protocol and explanation of the steps required

The secure third party R generates key $k_1$ to communicate with A and $k_2$ to communicate with B. A requests a key with which to communicate with B. R generates k un and encrypts: $E_{k_1}(k) = s1;...
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About a SETUP mechanism on ECDH

I'm following these three articles: Kleptography: Using Cryptography Against Cryptography, Kleptographic Attack on Elliptic Curve Based Cryptographic Protocols and Elliptic Curve Kleptography . In ...
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Key generation for DH key exchange - benefits of using KMI

Context We need to generate a key pair in order to perform DH key exchange with the other party. Some suggest to use a KMI solution (think: AWS KMS or like) in order to generate the key pair. ...
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Why should I export my private key instead of well known asymmetric crypto mechanism on openkeychain?

I'm trying to use password-store as password manager under linux. I created a private github repo with my gpg files in order to use it with other devices. I installed android-password-store app for ...
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Negotiating a session key, when only one public-key is exchanged via QR Code

Question I want to create a secure channel between a server and a client. It is only important that the client can verify the identity of the server, not the other way around. In my special case, an ...
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MitM with regard to unauthenticated clients

I'm trying to understand how man-in-the-middle attacks are prevented during key exchanges, and am confused by this Wikipedia statement: Use of mutual authentication, in which both the server and the ...
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Why does dragonfly key exchange need hunting and pecking?

The dragonfly key exchange scheme (as used by WPA3) received criticism because the way it chooses a generator of the elliptic curve group ('hunting and pecking') is a non-constant time algorithm ...
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Significance of y-coordinates in ECDH public key exchange

In the research paper Breaking the Bluetooth Pairing – The Fixed Coordinate Invalid Curve Attack? by Biham and Neumann, 2019, they talk about attacks in Bluetooth pairing, they state that in the ...
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Purpose of signing the signed prekey in X3DH?

I'm trying to understand the X3DH protocol used in Signal and many other end to end encrypted messaging apps. There are other questions on this site asking about why the signed prekey exists. I'm ...
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Use of nonces in the SIGMA protocol and not in C(2e, 2s) of NIST SP800-56a?

While reading the paper on the SIGMA: the ‘SIGn-and-MAc’ Approach to Authenticated Diffie-Hellman and its Use in the IKE Protocols (Krawczyk,2003), I noticed that in the "full-fledge" ...
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Good key update algorithms for key evolving schemes

In schemes like SAKE(Symmetric-key Authenticated Key Exchange) , the master keys (used to authenticate parties and generate session keys) are evolving, ie undergo transition $K=update(K)$. What is a ...
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Why is this authenticated Diffie–Hellman key exchange insecure?

I was searching for the information on authenticated Diffie–Hellman key exchange and found these slides. The author says, “Remember $$A\to B: (A, g^x, \operatorname{SIG}_a((g^x, B)))$$ $$B\to A: (B, g^...
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Can we say that password authentication contains registration phase, authentication phase and authenticated key exchange phase?

Authentication aims to validate the legitimate identity. The authenticated key exchange aims to establish a secure common session key. But can we say that password authentication scheme contains the ...
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MQV protocol and man-in-middle attack

Why MQV is said to be an “authenticated Diffie-Hellman” protocol? The process in the picture shows nothing about authentication. Besides, a man-in-middle can impersonate B to negotiate with A, because ...
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Isogeny-based AKE: what is the difference between Gal 1 and FTTY 1?

What is the difference between (a) the AKE scheme proposed by Galbraith (based on TS2 protocol) in https://eprint.iacr.org/2018/266.pdf (page 9-10); and (b) the AKE scheme proposed by Fujioka et al. ...
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Can libsodium's X25519 encryption construction be generalized?

It is my understanding that libsodium's sealed_box is based on X25519, a Diffie-Hellman function: By combining the X25519 key agreement with a symmetric cipher and having a recipient derive the ...
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Server distributing/sharing a symmetric key to one or more clients via an established secure connection?

I have a server and a client device that share two separate data channels that each need to have authentication and encryption protections. When a connection is made over data channel 1, it is secured ...
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Key Agreement between two nodes of a Wireless Sensor Network

Can there be a way to form a shared secret key between two nodes of a Wireless Sensor Network who are more than one hop away, simply on the basis of their IDs?
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Password-based chosen-basis computational Diffie-Hellman assumption

In Simple Password-Based Encrypted Key Exchange Protocols, the authors proposed a hard assumption as follows. Experiment $Exp^{pccdh}_{\mathbb{G}, n}(\mathcal{A}, M, N, X^{'}, \mathcal{P})$ $(Y^{'}, ...
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Transcript collisions and hash collisions in (password) key exchange protocol

In New Security Results on Encrypted Key Exchange, there is a Game 2 as follows: Game $G_{2}$: For an easier analysis in the following, we cancel games in which some (unlikely) collisions appear: ...
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How to encrypt with elliptic curve cryptography (ECC)?

I need to ask this, as I am not allowed to comment and don't quite understand an existing answer because I don't have a cryptography background and never looked into how ECC works. Why can't you ...
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Can we use HMQV in an asynchronous setting?

Following the HMQV paper, to perform a key-exchange, Alice ($\hat{A}$) and Bob ($\hat{B}$) perform the following: $\hat{A}$ generates the long-term key pair ($sk_A= a$, $pk_A =g^a$) and the ephemeral ...
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is it possible to achieve authenticated key agreement without using PKI or pre-shared secret?

After reading different techniques to achieve authenticated key-agreement (X3DH, HMQV, Asynchronous Ratcheting tree, An efficient protocol for authenticated key agreement, I understood that all these ...
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Do all PAKE assume that all parties already have a password?

I was looking for a means to perform a key exchange without relying on a PKI. I discovered Password Authenticated Key Exchange (PAKE) and after reading J-PAKE; I have the following questions: Do PAKE ...
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Diffie-Hellman Decryption with A, B, p, g, cipher Parameters

I have a Crypto assignment, trying different ideas for couple hours landed me nowhere. Supposedly during a Diffie-Hellman key exchange Alice sends bob an encrypted message, the message (cipher) is a ...
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Are there any known problems performing a One-time pad with 2 keys stored separately - AKA 2 part Symmetric key exchange over TLS

If this is something that already has a name, please tell me to look at that, but I have not been able to find one yet. I am considering this process for storing some data securely. I want to ...
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Is the password based key exchange secure even if the public key is known to adversary?

I am assuming the answer for part 1 to be a "NO" as the adversary knows the public key he can get the password by offline attack IN part 2 : the answer is "yes" as the public key is freshly generated ...

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