Questions tagged [key-exchange]

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

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What are the binding properties of post-quantum KEMs?

Performing a key exchange with post-quantum KEMs is very different to ECDH, which will likely cause vulnerabilities in protocols during the migration to post-quantum cryptography. One example is that ...
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The weakening of PQC as a result of lack of KEX?

As far as I can tell we don't have any good key exchange post-quantum candidates. SIKE was broken some time ago. It is possible to reach an authenticated shared secret by having the public key holder ...
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Ephemeral ECC refresh vs. simple hash ratchet

Some protocols employ ephemeral ECC key exchanges throughout the session. Such as the Noise framework. Is the rationale to do this simply because you can do it efficiently? To provide future secrecy ...
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RSA: Is padding necessary for key exchange?

When RSA is strictly used to exchange random shared secrets, is the padding scheme important for security or can it be omitted entirely? The party in possession of an RSA public key will generate ...
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Is any safe prime sufficient for a secure DH key exchange?

There are some very large safe primes listed here: https://en.wikipedia.org/wiki/Safe_and_Sophie_Germain_primes Would using any of them result in a secure DH construction? Generator is 2. The exponent ...
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Tor Key Exchange Client - Middle Node

I am currently exploring the workings of the Tor network, specifically how the Diffie-Hellman (DH) key exchange protocol is employed to establish shared secret keys between the client and each relay ...
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Impossibility of uniform generation in random world

I was reading Limits on the provable consequences of one way permutations by Impagliazzo and Rudich when I got stuck on a sentence. First of all, they define a polynomial relation that is any relation ...
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Key exchange for encrypted firmware update

I'm trying to implement encrypted firmware update functionality for an embedded device. The goal is to prevent reverse engineering of our firmware when the update files are shared with our customers. ...
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What is the difference between Post-Compromise Security and Backward Security?

Post-Compromise Security and Backward Security seem to mean that the attacker has obtained the communication key between two parties or groups in the current state, but cannot further obtain ...
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Graph-based key exchange

Alice and Bob fix a largish $n$, say $n = 1000$, and they publish a simple, undirected graph $G$ on $n$ vertices (more precisely, its adjacency matrix, or a similar form of representation). Moreover ...
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TR-31 Key Exchange Mode of Use

Using TR-31 key exchange, how is it possible to use restrictive modes of use, such as V (Verify only)? If Alice were to generate such a key, and send it to Bob, Bob would not be able to generate a MAC ...
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Can an attacker impersonate any party in a modified Needham-Schroeder protocol?

We are doing symmetric Needham-Schroeder protocol in university. We were provided a modified protocol and needed to answer the following questions. Original protocol: Modified protocol: Task a) An ...
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TLS 1.3 key_share capture without certificate exchange

I am working on an investigation on TLS 1.3. I've came across an article of qacafe where they shared a TLS 1.3 handshake sequence. Wireshark capture. In this capture you see that in the Client Hello a ...
Arthur Timmermans's user avatar
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Security of keys that are as long as the data

If both communicating sides end up with the same secret 3000-bit key, is it enough to XOR each byte of the messages with each byte of the secret key to make it secure? Wikipedia says it is, but I ...
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who creates the passkey (and how many will be created)? [closed]

Passkey is nice. The math is nice. The tech is nice. https://security.googleblog.com/2023/05/so-long-passwords-thanks-for-all-phish.html What I still dont see after sooo many hours: what software ...
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For TLS-PSK (pre-shared key), should non-ephemeral key exchange be preferred over ephemeral one?

TLS 1.3 specify two pre-shared key exchange modes, which are psk_ke and psk_dhe_ke. The former is a non-ephemeral key exchange ...
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Key exchange from discrete logarithm only

Diffie-Hellman key exchange is sometimes informally said to be hard under the discrete logarithm assumption in the chosen group. But if I am reading literature correctly, it actually uses a stronger ...
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Linux Kernel CryptoAPI key exchange and key derivation

I have a custom network and I want to implement a symmetric key exchange and key derivation mechanism with ECDH. I know that I need to use KPP API and ECDH helper functions, but I can't find any code ...
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How do I decrypt a key encrypted by my HSM under a ZMK?

I've generated a key using an HSM Thales PayShield and i have share it with a counterpart. I followed these steps: i generated key usign KG console command i use FK to form ZMK from clear components ...
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PCI compliance - use of ANSI X9.17 for export keys

we have a concern about a key export. We completed the migration to Key Block LMK in our environment (with HSM Thales 10K). Now, we have to exchange keys with third-parties that still use Keys in ...
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Clarification on the use of Key block Version ID with Thales HSM

Clarification on the use of Key block Version ID For the first time since we migrated to the Key Block we are exchanging keys with third parties, The keys were all generated by choosing Key Scheme &...
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Why NIST 800-56A rev3 does not use cross secret calculation in C(2e, 2s, ECC CDH) scheme?

In the NIST 800-56A rev3 "Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography" in section 6.1.1.2 "(Cofactor) Full Unified Model, C(2e, 2s, ECC ...
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How does TLS 1.3 restrict the Diffie-Hellman parameters to ones that are known to be secure?

In previous versions of TLS, the choice of the Diffie-Hellman parameters was up to the participants. This resulted in some implementations choosing incorrectly, resulting in vulnerable implementations ...
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Mutual authorization using a pre-shared key

I'd like for two machines on a network to be able to prove to each other that they both have knowledge of a pre-shared secret, without revealing the secret to each other. Let's assume that all traffic ...
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Authenticated Key Exchange of Kyber.AKE

I have some questions about the setting of the one-way authenticated key exchange of Kyber.AKE as defined in section 5 of the paper. How does $P_2$ authenticate itself to $P_1$? It is not obvious to ...
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How can I send someone a large file safely without using key exchange protocols (for encryption)?

I recently took an exam where one of the questions was roughly the following: You need a specific way for sender S to send a large file M to a receiver R with their secret-public key pair, without ...
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Where is the cryptography library that support group signature?

Finding a cryptography library to implement various application features is not difficult nowadays, thanks to options like NaCl, Google Tink, PyCA, and OpenSSL. However, I've been struggling to find a ...
American Corn's user avatar
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Two way key transport?

For a KEM mechanism like RSA, Kyber, etc. is there it usually worth doing key trapping/key encapsulation both directions in a key exchange? By this I mean: Alice wraps a symmetric key and sends it to ...
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DH Finding A Public Key from Public key and shared secret

Is there a known feasible method for determining an unknown public key from a Diffie Helman shared secret and the other public/private key pair? This would be rarely useful, but I am curious if the DH ...
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Compute key size in Hyperelliptic Curve Cryptography

I am trying to implement a basic Diffie-Hellman key exchange using ECC and HECC of genus 2 and 3 and compare them. However, I am a bit confused about the concept of key size in HECC. In ECC, from my ...
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A tensor-based Diffie-Hellman exchange

Below is a description of a "cube" Diffie-Hellman, based on commuting matrix actions on tensor products. Some questions: References for something similar? Obvious flaws, is this a terrible ...
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Why did post-quantum key exchanges go extinct?

On July 5, 2022, NIST chooses one KEM (Key Encapsulation Mechanism) as a PQC standard and 4 KEMs as four-round candidates. Why aren't there any key exchanges? Similarly, KEMs are usually studied in ...
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What is the most secure hybrid cipher suite(Library) possible today?

What combination of public key cryptography (DH) and symmetric key cryptography is currently available that is (subjectively) as secure as possible over other ciphers (AES,curve448) when security is ...
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A perfect key exchange similar to the One Time Pad

The one time pad is unbreakable because each message could be one of many, and each one is equally likely. Is it possible to do this with a key exchange? (So if someone records the key exchange, there ...
undefned's user avatar
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McCallum-Relyea exchange on x25519 elliptic curve

Background I have a degree in electronics engineering, I'm not bad at programming with many languages, but I'm not that good at cryptography, I'm just able to use that from libraries, and I understand ...
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RSA Key Exchange Attack [closed]

I am curious what is an attack that the RSA Key Exchange algorithm is vulnerable to that Diffie Hellman Key Exchange is not vulnerable to? I know Diffie Hellman is prone to Man in the Middle attacks ...
CryptoGuru's user avatar
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Explanation of Burmester-Desmedt group key exchange and Ingemarsson-Tang-Wong (ITW) group key exchange algorithm

I know that both algorithms are similar to the Diffie-Hellman key exchange and are used for exchanging secret keys in a group but I still cannot figure out the key differences between both algorithms. ...
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Can you use MITM to hijack a public key meant for key based signing?

After reading "Verify the identity of sender" , which was part of an answer on StackOverflow, I was wondering if the following is possible: Based on part II, if I am sitting between Alice ...
Tom's user avatar
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Blom's key distribution

Having a difficult time wrapping my head around the Blom's key distribution. I found an online resource to understand this but still couldn't get it. I am attaching the screenshot from the book where ...
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Defending MITM attacks during key exchange

As far as I know, key exchanging algorithms are vulnerable to an active MITM attack. Let A (Alice) and B (Bob) be parties with no secret information. An adversary C playing man-in-the-middle ...
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Mapping DH / DHE p & g params to a group

I'm doing a small code that performs a simple SSL/TLS analysis and I'm stuck on determining the size of the key exchange in the case of DH / DHE. If I take the following example (wireshark capture) : <...
Akerces's user avatar
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How does TLS 1.3 provide authentication without using the public key to verify that the server has a private key?

In the TLS 1.2 handshake, after checking the certificate, the public key from the certificate was used to encrypt the data to create a symmetric encryption key, hence the authentication took place on ...
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minimal public-key authenticated encryption protocol

One party (master) wants to send data to another party (slave) over an insecure channel using public-key encryption and signature schemes such that: master is authenticated, data is confidential, ...
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How to evaluate efficacy of new public-key cryptosystems

Suppose I had a new public-key or key exchange protocol. How do I objectively evaluate it so as to determine if it is worth sharing with the broader community? Whenever developing a cryptosystem, it ...
user918212's user avatar
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Forward-Secure AKE based on post-quantum KEM?

I am looking for authenticated key exchange protocols (AKE) based on a generic key encapsulation mechanism (KEM) and providing full/perfect forward secrecy. Optionally, the protocols should offer ...
Felix H.'s user avatar
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1 answer
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Encrypt messages for two-participants chat

I need a chat between two users and I obviously want to make it as secure as possible. I am, by no means, a cryptography expert, so I turn to you guys for some advice. Because I like the idea of ...
SparxDev's user avatar
2 votes
3 answers
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Can a man in the middle tell what kind of encryption you're using from a key exchange?

Encryption schemes typically are built on the idea that even if a man in the middle attacker knows exactly what kind of encryption you're using, they cannot decrypt your messages without the key. ...
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In a Diffie-Hellman key exchange Find this key and compute the shared secret key k

Hi I struggling to find the answer of my schhol exam, can anyone help me . In a Diffie-Hellman key exchange the multiplicative group of integers modulo p is used with the parameters p = 59, g = 3 mod ...
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Commutable and Composable Asymmetric Encryption/Decryption

I have a need for the following encryption properties: $f(g(v_\text{plaintext}) = v_\text{ciphertext}$ needs to be decryptable by $f^{-1}(g^{-1}(v_\text{ciphertext}))$ and $f$ and $g$ need to be ...
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How is Diffie-Hellman linked to AES?

I have just learnt about Diffie-Hellman and AES. However, I cannot seem to understand how they link. My initial idea was that Diffie-hellman is used to transfer a key for AES decryption. After further ...
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