Questions tagged [key-exchange]
Key exchange protocols allow two parties to produce a secret session key over a public channel.
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In end-to-end encryption, doesn't the server need to be trusted?
Applications like WhatsApp use end to end encryption. WhatsApp says that only the users share a specific key and no third party can view the messages. But I do not understand how the two users agree ...
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ECDSA vs ECIES vs ECDH
Recently I started studying Elliptic Curve Cryptography and I just loved it. I want to transfer some big data (like 3KB), What is the best method, ECDSA, ECIES, or ECDH (and why)?
I am confused, how ...
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Differences between the terms "pre-master secret", "master secret", "private key", and "shared secret"?
Both crypto.SE and security.SE have excellent Q&As about how TLS generates session keys (I have linked some at the bottom).
In reading these threads I'm having troubles with terminology since the ...
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Can one generalize the Diffie-Hellman key exchange to three or more parties?
Does anyone know how to do a Diffie-Hellman or ECDH key exchange with more than two parties?
I know how to do a key exchange between 2 parties, but I need to be able to have a key agreement between 3 ...
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Is Diffie-Hellman mathematically the same as RSA?
Is the Diffie-Hellman key exchange the same as RSA?
Diffie Hellman allows key exchange on a observed wire – but so can RSA.
Alice and Bob want to exchange a key – Big brother is watching everything.
...
joe armstrong
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Does the generator size matter in Diffie-Hellman?
For the Diffie-Hellman protocol I've heard that the generator 3 is as safe as any other generator. Yet, 32-bit or 256-bit exponents are sometimes used as generators. What is the benefit of using ...
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How can I make sure non-open source programs are really using end-to-end encryption?
Without going deep into math, is there a way to make sure that non-open source programs like WhatsApp, FaceTime, Zoom, etc. are really using end-to-end encryption instead of just 'regular encryption' (...
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How does one verify a GPG/PGP key revocation?
After revoking a key and sending the revocation to MIT's keyserver, I noticed that the key is listed as such:
...
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Multi-party encryption algorithm
To give some foreground information: I acknowledge that I am a cryptography newb and not by any means an expert (and probably never will be).
In a recent CS class we had several assignments writing ...
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What is the post-quantum cryptography alternative to Diffie-Hellman?
Post-quantum cryptography concentrates on cryptographic algorithms that remain secure in the face of large scale quantum computers. In general, the main focus seems to be on public-key encryption ...
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What makes Quantum Cryptography secure?
This is my current understanding of how Quantum Cryptography works: (The first bit is Quantum Key Distribution)
Alice sends a beam of photons to Bob through a quantum channel such as an optical fiber. ...
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Why do we need Diffie Hellman?
Diffie–Hellman offers secure key exchange only if sides are authenticated. For authentication, sides are using public/private key. So if side A knows the public key of the side B, then A can simply ...
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Is there any SRP-like key exchange only using "standard" cryptographic primitives?
I am looking into PAKEs (password-authenticated key exchanges), and it seems like SRP (Secure Remote Password) is essentially the de-facto standard.
However, implementing SRP actually requires doing ...
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Is HTTPS secure if someone snoops the initial handshake?
Let's say I'm on an open wireless network that's being actively sniffed and I connect to an HTTPS site. Even though my subsequent traffic is encrypted, couldn't the sniffer use the data from the ...
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What are the advantages of a static ECDH key?
What are the advantages of using "static-ephemeral ECDH" over "ephemeral-ephemeral ECDH"?
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Status of Algebraic Eraser key exchange?
Algebraic Eraser™ is a relatively new asymmetric key agreement protocol (also designated the Colored Burau Key Agreement Protocol), based on a simultaneous conjugacy search problem in a braid ...
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Relation between Key-exchange and Public-Key encryption schemes
Recently we have seen a lot of papers on Post-quantum key-establishment (key encapsulation mechanism or Key-exchange), largely due to the standardization call of NIST for PQ-protocols. However, most ...
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Curve25519 over Ed25519 for key exchange? Why?
I've been reading up on the Signal Protocol (in this PDF) and it seems to be using Curve25519 for ECDH and EdDSA (with Ed25519) for signatures.
My question is why not use only Ed25519?
This ...
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How is the key shared in symmetric key cryptography?
Symmetric key cryptography is an encryption system in which the sender and receiver of a message share a single, common key that is used to encrypt and decrypt the message.
Is the key public or it is ...
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Why do we need asymmetric algorithms for key exchange?
In SSL protocols, both symmetric and asymmetric algorithms are used. Why is it so? The symmetric algorithms are more secure and easier to implement. Why are asymmetric algorithms usually preferred in ...
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What Diffie-Hellman parameters should I use?
After reading this article, I started wondering how should I approach the problem of choosing p and g params in 1024-bit Diffie-Hellman key exchange.
In my project, I am going to establish keys ...
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Is quantum key distribution safe against MITM attacks too?
i read this recently: http://www.newscientist.com/article/dn12786-quantum-cryptography-to-protect-swiss-election.html
and some parts of this: http://en.wikipedia.org/wiki/Quantum_key_distribution
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Is there a pen-and-paper way to securely share a secret via public key encryption? [duplicate]
We have several questions tagged pen-and-paper talking about encryption, hashing, signing, etc. but no question asks about exchanging a secret via public key encryption in a secure way.
Does any ...
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How exactly does ASKE (Alpha Secure Key Establishment) in Zigbee work?
I am working on Zigbee security. For key establishment, some approaches are given in Zigbee. Some of them are:
ASKE (Alpha Secure Key Establishment),
ASAC (Alpha Secure Access Control), and
SKKE (...
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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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ECDH or RSA more secure for symmetric key wrapping?
Suppose a message is encrypted with a symmetric block cipher with a random key. RSA is often used to wrap the symmetric key using the recipient's public key.
In this case, the size of the message is ...
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Key exchange using ECDH vs ECIES?
I'm a beginner to ECC crypto programming. Can anyone explain to me the difference between using ECDH for shared key exchange and the use of ECIES by encrypting a shared key with the public key of the ...
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AES encryption using a Diffie-Hellman key exchange
I have two systems which need to encrypt their communication by AES-128. The key for the AES encryption should be exchanged with the Diffie-Hellman (DH) algorithm.
Now, I've read about DH and got a ...
Neomatik
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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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RSA-based authentication and key-agreement protocol
An authentication and key-agreement protocol between devices shall mutually demonstrate their identity, and establish a shared random secret $R$ suitable for securing later communications.
To that ...
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What is the "shared secret" used for in IPSec VPN?
Can somebody explain what the "shared secret" and "password" do when opening/creating a VPN tunnel?
In this specific case I setup a VPN to my Fritz!Box and I had to provide a shared secret (which was ...
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Authenticated DH, what protocols are secure?
I read about STS + variants being insecure in the SIGMA paper, which then proposes SIGMA as a replacement. Are the SIGMA variants still considered secure or are there some other protocol that's ...
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WhatsApp end-to-end encryption
WhatsApp offers end-to-end encryption. However, when I start using it on a second device such as a PC running Windows, I can decrypt incoming messages without providing any private key into my second ...
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Does perfect forward secrecy (using DH or ECDH) imply quantum resistance?
Does perfect forwarding secrecy, as used for e.g. the DHE_ and ECDHE_ TLS ciphersuites make it impossible for quantum analysis ...
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Quantum key distribution simulation
I'm looking for a simulation of the Quantum Key Distribution protocol. Does anyone here have one that they could recommend?
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What asymmetric key exchange algorithms are known besides DH?
On Wikipedia, a lot of the subjects that are said to be different key exchange methods are often just protocols that incorporate the Diffie-Hellman algorithm into them. The only other key exchange ...
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What current authenticated key exchange standards exist?
If neither of the 'big two' of TLS Handshake and IKE are appropriate in a given situation, what alternative Authenticated Key Exchange (AKE) standards exist and are recommended?
Many protocols have ...
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How should I check the received ephemeral Diffie-Hellman public keys?
In my application I'm doing a DH key exchange, where both sides generate their
own ephemeral key. No static keys are used. I am trying to make my
application resistant against an active attack and ...
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Why would the use of Curve25519 in Dragonfly leak information?
An answer explaining Dragonfly, a form of key exchange used in WPA3, has an interesting footnote:
One final note: reviewing the Firefly RFC, I see that it would (as written) leak some information ...
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Is HIMMO For Real?
I've come across something out of Philips Research called HIMMO Key Pre-Distribution Scheme (https://eprint.iacr.org/2016/410.pdf and https://www.ietf.org/proceedings/96/slides/slides-96-cfrg-2.pdf) ...
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PAK Diffie-Hellman vs. sharing high-entropy key
In order to setup an authenticated shared secret key between two clients, I am faced with the choice between two possibilities:
Let users set a (low-entropy) shared password and then perform some ...
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Differences between “NewHope” and “NewHope-simple”
The well-known paper described a key exchange (KE) scheme named "NewHope" on USENIX 2016. The authors then proposed "NewHope-Simple" - a PKE/KEM scheme. They also submitted "NewHope for NIST" - ...
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Exchanging encrypted messages, and decrypting without a public key?
I know very little about encryption, but I was hoping someone could shed light on this cipher text exchange scheme I worked out in my head this morning:
Bob wants to send Alice a message but doesn't ...
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Number of LWE samples in NewHope
This is regarding the number post-quantum key exchange protocol New-Hope (https://eprint.iacr.org/2015/1092.pdf). In the paper, we can see that the number of samples generated by the protocol is $2n$ ...
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Perfect Forward Secrecy with Pre-shared Key
I've recently been looking at how to do perfect forward secrecy on a unidirectional connection (server can only push messages to client, client cannot respond).
What I've come up with is the idea of ...
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Can I use a key-derivation-function as the hash function H in SRP?
In the Secure Remote Password Protocol, the verifier must be stored on the server. In the case of a server compromise, an attacker could obtain these verifiers. If nobody reused passwords, this ...
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Security of a security protocol for key exchange, using symmetric-key cryptography
This is an exam question:
$A \to B$: Alice, $nonce_A$
$B \to A$: $nonce_B$, $E_{k_{AB}}(nonce_A \| k_1)$
$A \to B$: $E_{k_{AB}}(nonce_B \| k_2)$
Alice and Bob both compute $k_s$ = $k_1$ xor $k_2$
$...
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Matrix key exchange
Given is a square matrix $M$ over a field $F$, we have a key exchange with the following conditions:
Person $X$ sends a message to Person $Y$: $C_{1}=AM$, where $A$ is a randomly chosen square matrix....
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Trouble with diffie-hellman groups
Is anyone able to point me towards a known-to-be-good diffie-hellman group? I currently use group 24 (RFC5114, 2048-bit MODP Group with 256-bit Prime Order Subgroup). It came to me that this group is ...
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Small subgroup confinement attack on Diffie-Hellman
I am trying to understand the small subgroup confinement attack on the Diffie-Hellman algorithm. I will present the attack and try to explain why it works.
Small subgroup confinement attack on the ...
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