Questions tagged [key-exchange]

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

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How modern messengers encryption keys can't be hacked

I dont know is this question more like reverse-engineering or cryptographic. Why governments are hunting for encryptions keys? Aren't they delievering by the network the same as the encypted messages? ...
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Curve25519 key exchange in detail

So I'm trying to understand how the key exchange with Curve25519 works. I read the original Paper from Bernstein "Curve25519: new Diffie-Hellman speed records", but I still got some questions. First ...
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Why is Curve25519 mostly used for key exchange?

When i studied the Applications where Curve25519 is used, i found out, that it is mostly used for the key exchange. Examples are the Signal Protocol and Threema. I know, that Curve25519 has a pretty ...
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CP-ABE secure key management

I want to use CP-ABE (Ciphertext Policy- Attribute-Based Encryption) schemes for multicast communication. How can I share both the public key and secret key among the user? How I do set up an ...
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Standards for finite-field discrete log cryptography

The NIST and TLS standards for Diffie-Hellman key exchange over a finite field all work in a subgroup of ${\mathbb Z}_p^*$ having prime order $q$, where $p = 2q+1$. On the other hand, DSA has a larger ...
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Research topics related to cryptography and Hamiltonian cycles

I am very interested in pursuing a research where I can show an application of Hamiltonian cycles in Cayley graphs of some group such as reflection groups to the field of cryptography. But currently ...
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DHE parameters: which parameters need to be random each time?

In DH key exchange, first, both parties need to agree on a generator $g$ and prime $p$. After that each party computes its key (party A: $g^a \bmod p$) and (party B: $g^b \bmod p$), then they exchange ...
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Interactive ECDHE Authentication With Numeric Code

Trying to simplify my question, keeping only core concepts. Proposed solution: Both user devices generates ECDHE key pairs. Send pub keys to each other. Generate shared secret. Device that requests ...
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Does the order of the “Finished” messages matter in SSL/TLS?

In SSL 3.0 and TLS versions 1.0 through 1.2 the last two messages are the "Client Finished" followed by "Server Finished" messages. These messages include an encrypted (under the established session ...
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For Diffie-Hellman, why is a g value of p−1 not a suitable choice?

I am currently learning about the Diffie-Hellman key exchange. I understand that for a $g$ of $1$, the resulting key would always end up as $1$ which would obviously not be secure. I read that the $p\...
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Using PSK starting a new session, encrypt the new session key with old, or sign a derivative to be used on the old key?

I have two endpoints that go through a middleman. Both have a pre-shared and secure key, 16bytes to be used with ChaCha20-Poly1305. Extremely constrained device. No packet larger than 100 bytes total. ...
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Trying to understand how the same secret key end up being calculated between Alice and Bob

This is basically a duplicate of this question which was not answered very clearly. From the documentation, these are the calculations that happen for Alice to compute the shared secret key: ...
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Why is there no “ephemeral non-DH EC” key exchange in TLS?

In RSA key exchange, the client picks a premaster secret and encrypts it with the RSA public key in the server certificate, and sends it to the server. This offers no forward secrecy. In ECDHE key ...
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what does output parameters of lwe estimator stands for?

I want to use lwe estimator to find classical and quantum security of my proposed key exchange protocol. On this website, I want to understand the output of sage code on lwe estimator given bellow. ...
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On an EKE (Encrypted Key Exchange) what would happen if asymmetric key would be symmetric?

On EKE where the user sends a password encrypted public key and receives a password encrypted and public key encrypted secret key. What would happen if these asymmetrical keys would become symmetrical?...
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Key Exchange vs Key Encapsulation

From what I understand, the steps of a key exchange protocol are Alice and Bob each encrypt something using their public key and private key and send the result to each other Alice and Bob each do ...
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In the SIKE known answer tests, why is there only one secret key?

I'm looking at the SIKE known answer tests and am realizing that I'm confused on all the different terms in a Diffie-Hellman key exchange. From the Wikipedia page, I would think there would be a ...
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Security of Half-Key Key Management Scheme

I am interested in algorithms that consume as less space available on a memory, for low consuming power devices such as wireless nodes. From a search I have found this article here: https://dl.acm....
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How keeloq keyfob exchange key with receiver in the first place?

After reading a lot of articles and the microship maunal for keeloq IC, I think I understand how the encryption and decrytion works. If I understand correctly, however, the decryption require the ...
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86 views

DH Key Exchange Protocol

Since I am not able to comment under the topic, I would like to ask here why in question 2 old post, we cannot distinguish the two distributions, even with unlimited computational power? Also, what ...
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Diffie-Hellman key exchange protocol with finite field GF(2^5)

In a Diffie-Hellman key exchange protocol, the system parameters are given as follows: finite field $GF(2^5)$ defined with irreducible polynomial $f(x) = x^5 + x^2 + 1$ and primitive element $\alpha= ...
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Is the first Nonce exchange between Alice and Bob in Needham-Schroder key exchange protocol redundant?

For the Needham-Schroder protocol, assuming Alice and Bob are both able to guarantee each other's public keys (e.g. through a Certificate authority), the protocol is 1) A sends to B: $E_{publicB} [...
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Why RSA-KEM is more secure than Textbook-RSA?

I am studying RSA-KEM but I can not see why it should be as secure as padding RSA messages (e.g with RSA-OAEP) when exchanging a key between two parties (say A and B). It is easy to see that Textbook-...
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Key-Agreement & Key-Transport for Symmetric Authentication System

Question: I want to know what kind of Master Key sharing process is pursuit on Symmetric encryption environments (strictly symmetric, also in the key sharing scheme). As I am aware there are several ...
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Is there value in performing signature during key exchange?

I looked around the net, however I couldn't see anything authoritative on this. If one is using something like libsodium to perform key exchange (using x25519), is there value in using Ed25519/...
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NTRU Bilateral Key Exchange

With the NTRU scheme, is the key exchange only done by encrypting a symmetric key with the recipients public key (+ authentication) or can something similar to DH/ECDH be done, where public ...
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Key exchange and authentication using libhydrogen

I have been able to exchange session keys on two devices using Libhydrogen's Key exchange using the N variant method. I also want to authenticate both devices to have some protection against the Man ...
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Is a Diffie-Hellman scheme in which parties always use the same public keys vulnerable?

I have come across a couple of protocols in which the public keys of the parties are static across conversations, even with different users. Something about this makes my hairs stand on end but I can'...
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Simply using password as a third “private key” for PAKE

I'm reading through the development of PAKE protocols, starting with EKE and SPEKE, their potential pitfalls, and what motivates their protocol choices. And I've been wondering, what is wrong with the ...
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Diffie-Hellman Key Exchange attack on small secret keys [closed]

The question as the title suggests is based on the key exchange with Diffie-Hellman protocol and is something like this: *"We have intercepted a communication between Alice and Bob: intercepted-...
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Is there a key exchange protocol that requires only one message?

Say I want to exchange a secret with someone, but I only get to send one message to the other person, and then we encrypt with that secret. Diffie-Hellman and ECDH require multiple messages to be sent ...
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HMAC based Key exchange

Alice and Bob need to share public keys to sign/verify ephemeral keys. They have a secret key $K$. Alice generates a 32 bytes random number $A$, computes $\operatorname{HMAC-SHA256}(K, M||A)$ and ...
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Is there any problem to reuse the prime p, g and a in Diffie-Hellman?

Suppose I always reuse p, g and a in DH and there is someone monitoring my communication. Is there a way this person can use this to perform some kind of attack to me? I believe that reusing p and g ...
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Is CECPQ2 forward secure?

Is the CECPQ2 key exchange, as deployed by Google[1] and Cloudflare[2] in TLS 1.3 forward secure against quantum computers? I know that it is using HRSS+SKY as the post-quantum part of the key ...
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Why are PAKE protocols not widely used?

While there are plenty of PAKE protocols, especially those augmented ones which are practical in C/S model, actually they seem to be not widely used. Even TLS-Standardized SRP, the most popular one ...
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Is this PGP key exchange secure?

I am currently trying to create a secure key exchange between two parties. I have a good implementation of PGP that works well for my app, but my DH is really slow and doesn't work well; so I was ...
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Prevent a Man-In-The-Middle attack whilst transmitting a PSK for first time

I'm developing a network where two parties that want to join both compute ephemeral ECC keys for a key exchange, to create an encrypted connection. I plan to authenticate these keys by signing them ...
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Ensure Data Integrity In An ECDH Key Excange

Been playing around with the inner workings of onion routing and I have a problem. If I wanted to send the 2nd node of a relay network an ephemeral ECC public key, it has to go through node 1, so that ...
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Size of Key Material of TLS_DHE_RSA_WITH_AES_256_CBC_SHA

What is the size of key material required for generating MAC keys, encryption keys and IV when use TLS_DHE_RSA_WITH_AES_256_CBC_SHA ? How to calculate it?
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Is this pairing scheme for establishing trust between two devices with self-signed TLS certs secure from MITM?

Assume two devices (A and B) with self-signed TLS certificates (this part can't change). We want these devices to trust each other. One way to do this is to simply copy A's cert over to B's allowed ...
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Calculate shared key having A public Key and B private Key (Diffie Hellman)

I cannot understand how this works. $\text{A}_\text{public} = g^a \bmod p$ $\text{B}_\text{private} = \text{B}$ $\text{g} = p$ I also have $p$, I need to get the shared key, that I know both $\...
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Decrypting arbitrary numbers with RSA

I want to construct a hash-chain where I want to share millions of small AES-128 keys with Bob over a period of time. Bob should not be able to predict the future keys if he knows the past keys. I ...
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TLS_DH_RSA_* cipher, how can static DH use an RSA certificate?

I am confused about TLS_DH_RSA_* ciphers because, for DH to work, the server certificate has to include a DH public key, but for server authentication the server certificate needs an RSA public key. ...
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Is it safe to use shared secret as a symmetric key in one way communication?

I have a one way communication from one device to another, which needs to be secure and there cannot be any feedback in the other direction. Now both sides happen to have ECC P-256 key pairs and they ...
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Understanding need for PKI

For simplicity let's say I only have RSA and AES on my hands and I want Alice to talk with Bob over a secure channel. With secure I am implying no MITM and Alice and Bob know they are talking to each ...
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Struggling to understand Perfect Forward Secrecy

From the definition on Wikipedia: In cryptography, forward secrecy (FS), also known as perfect forward secrecy (PFS), is a feature of specific key agreement protocols that gives assurances that ...
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How to handle multiple key-agreements

If I would use two different key-agreements e.g. SIDH and ECDH how would I handle these both derived keys? Is there a different between XOR or SHA-256 the two keys? (Would one reduce the level of ...
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Why are the session keys in DHKE for different values of 'a' the same?

In a DHKE scheme with the a prime p = 467. an element g = 4. The element 4 has order 233 and generates thus a subgroup with 233 elements. after Computing the common key for A. a=400, b=134 B. a=167, b=...
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Calculation of failure probability in basic Ring-LWE-DH key agreement

This is the basic unauthenticated Ring-LWE-based Diffie-Hellman key exchange, based on Peikert's Ring-LWE KEM: (from BCNS15) Alice and Bob have shared public polynomial $a$ randomly drawn from $R_q = ...
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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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