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

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Establishing encryption key using shared secret

I need to establish some security on a network of 8 bit microcontrollers. very limited RAM, CPU and packet sizes. I have zeroed in on a shared secret based scheme. Setting up shared secret is out of ...
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1answer
18 views

SSH rekey security implications

When an SSH session is rekeyed due to either the time limit or data limit for rekeying having passed, does the Diffie-Hellman exchange take place within the encrypted channel provided by the existing ...
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36 views

Deriving 2 shared secrets from one private key and 2 different public keys

I have a key pair, say $(d, Q)$. I send my public key $Q$ to 2 different people. I also get their public keys $Q_1$ and $Q_2$. Now I can derive 2 shared secrets, $d*Q_1$ and $d*Q_2$. The 2 other ...
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46 views

Key exchange using ECDH vs ECIES

I'm a beginner to ECC crypto programming. Does any one explain to me the difference with using ECDH for shared key exchange and use of ECIES by encrypting shared key with the public key of the ...
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66 views

Sending the next one-time pad key in this one-time pad message? [duplicate]

I am doing a research project on cryptography next year, and I'm really new to cryptography. This isn't some really advanced thing or anything, and I'm just trying to come up with something basic. ...
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1answer
105 views

About Primitive roots mod n in Diffie-Hellman [duplicate]

I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers $\mod n$). In some crypto papers and documents I've read that $g$ needs to be a primitive root mod $n$ ($g$ ...
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1answer
50 views

Exist this chat protocol?

I want to implement a secure chat on mobile. I like to know if the following protocol for key agreement that use any asymmetric encryption exists: Suppose Alice and Bob are two clients of the app. ...
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1answer
57 views

Rsa Key Exchange Protocol

Moderators: Maybe this question will be move to other sub-forum. My question is Anybody know some link with a tutorial of how implement the RSA key exchange protocol using java for chat comunication?
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1answer
36 views

Ephemeral Diffie-Hellman in a symmetric crypto context

I'd like forward secrecy in a case where the two sides have a shared long-term symmetric key. I intend to use AES in GCM. It looks like ephemeral Diffie-Hellman is the best way to generate the session ...
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3answers
126 views

Is what i'm trying to do safe?

What both parties have: Server Master Secret (MS) Server supported versions (Svers) Agreed upon version (ver) Client Master Secret (MS) Client supported versions (Cvers) Agreed upon version (Ver) ...
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1answer
33 views

Renewing session key

I have a system which (should) never shut down, there are keep alive messages every 30 seconds and normal traffic is very variable, might be a few KB/sec might be nothing more than the keep alive ...
2
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1answer
113 views

Is this variant of SRP useful?

I'm interested in using a modified form of SRP as a peer-to-peer authentication method. Since neither side is acting as a host, one of the primary design goals for SRP (that the client doesn't need ...
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75 views

Authenticated EC key exchange without a signing/signature scheme?

From my little understanding of EC-based authenticated key exchange protocols, I believe that it is not possible for authenticated key exchange without a signing/signature scheme. Is this correct? ...
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1answer
49 views

Different keys for clients but 1 key on server

Is it possible to have different keys on alot of (embedded) devices and just have 1 key on a server (to witch all these devices connect)? The main point here being when 1 device is compromised this ...
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2answers
47 views

correct usage of keys and nonce

I've being studying up on AES, GCM, CBC, HMAC and a lot of other primitives and am somewhat ( a little bit, perhaps) familiar with them however I am still a bit weary on the use of the keys and nonce. ...
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35 views

EC based password authenticated key exchange protocol

I would like to know: What is the currently best (efficiency and security wise) known EC based password authenticated key exchange protocol? (i.e. is there any EC based protocol may be similar to DH ...
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0answers
66 views

Popularity of ECMQV authenticated key agreement protocol

I've got a few ECMQV related questions: Why is ECMQV a more efficient EC-based authenticated key agreement protocol? Why is ECMQV so popular? Is it because no other protocol of its strength exists? ...
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1answer
52 views

Rationale of “r” AES key use in OTR version 3 AKE protocol?

I just tried to review & understand AKE (Authenticated Key Exchange) protocol as defined in OTR secure messaging protocol version 3 here , and aiming to achieve Perfect Forward Secrecy I am a ...
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36 views

Using a Secure RNG in Probabilistic Fair Exchange

I am attempting to implement probabilistic fair exchange described in Probabilistic Non-Repudiation without Trusted Third Party. A secures a message using AES with 512 bit keys (in my ...
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1answer
60 views

New to cryptology, studying key exchange

I'm just getting an overview of some of the concepts in key exchanging at the moment, and I'm a bit disoriented on a few topics, namely key stretching, key derivation functions and perfect forward ...
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1answer
69 views

Key Confirmation Attack [Key Distribution Center (KDC)]

Okay this is how I understood it according to this: Alice $A$ establishes a connection to $KDC$ and prepares for session key Exchange $k_{ses}$ $A$ encrypts the request with her key $k_A(A, B)$ ...
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82 views

Key exchange using hash function

Consider two types of attackers on a key exchange (KE) protocol and subsequent communication between the parties which used this KE instance to establish a secure communication key. Attacker Eve ...
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28 views

WPA and WPS: connection method [closed]

Do clients use WPS every time when they connect to a WPS-enabled AP? Or maybe they do it just the first time and then they switch to a normal WPA/WPA2 key exchange? If the latter, it's possible for ...
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Attack on key exchange with authentication

Suppose the honest parties - Alice and Bob - exchange public key in person/via telephone so that attacker can only eavedrop on the line. Alice has hashed the public key using a collision resistance ...
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1answer
92 views

Beginner question about secure communication with one user using DES

I am currently learning about encryption and I was asked a question: If a customer only had a DES system how could I secure messages as DES is not secure. I was researching this and I came across a ...
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3answers
111 views

How does $g$ being a generator imply Diffie-Hellman's correctness?

In the Diffie-Hellman protocol for key exchange over an unsecured channel, we choose $p$ and $g$, where $g$ is a generator of $\mathbf{Z}_p^*$. However I want to know why this assumption makes the ...
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46 views

Key establishment protocols other than Diffie-Hellman

Are there any key agreement/exchange/establishment protocols which are NOT based around the Diffie-Hellman protocol or handshakes using public key cryptograaphy? DH seems to form the basis of this ...
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1answer
78 views

Can you exchange a shared key without any hardness assumptions?

Imagine that P=NP, and one way functions don't exist. Can two people end up with a random shared key of arbitrary length, if every exchange is public? They have true RNGs, and know who they are ...
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61 views

Is it possible to perform one-way Diffie-Hellman MITM?

Here's something that is bugging me recently: suppose that me and my friend establish an OTR session and - as a result of that - DH key exchange is performed. My friend verifies my key, but I cannot ...
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1answer
103 views

Attacker in a key exchange

I'm having trouble with the following question: $X(A) \rightarrow B:(A,N_X)$ $B \rightarrow X(S):(B,((A,N_X,T_B),K_{BS}),N_B)$ $X(A) \rightarrow B:(((A,N_X,T_B),K_{BS}),(N_B,N_X))$ ...
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1answer
92 views

RSA Protocol behind Yaksha Security System

So I'm reading over the Yaksha Security System and see it is based on the RSA cryptosystem and a centralized server, easy enough. What I'm slightly confused on is the math behind the related keys. It ...
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1answer
104 views

What are the potential (major) flaws in this security scheme?

It’s been a few years since I read anything involving crypto. I’ve come across this scheme and I wonder how secure it is: Alice generates an RSA keypair (we assume Alice is using proper random ...
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DHE key exchange. Is it really secure?

Context I recently came across a video on the net showing the process of key exchange in Diffie Hellmann. Alice and Bob want to communicate. Eve is the (wo)man in the middle. This video is the ...
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Why is it hard to calculate Logarithm on Diffie Hellman?

i read something about Diffie Hellman. What i don't understand: Alice selects a randomly generated Number, calculates X = g^x mod p and sends X to Bob. If she calculates g^x, she needs to calcluate ...
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168 views

What are the advantages of Certificate Authority and Key Distribution Center over each other?

I want know difference among them. What are advantages/disadvantage of one on other?
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1answer
66 views

How to use the key from a Diffie Hellman exchange? [closed]

I watched a YouTube video about Diffie-Hellman called "Diffie-Hellman Key Exchange", and it said after doing some modulo operations with the public modulus and generator and the random private ...
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39 views

impersonating attack against a protocol

recently I'm reading Efficient eCK-secure Authenticated Key Exchange Protocols in the Standard Model, and I sense that the scheme in the following(the reader can refer to the paper for details) is ...
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exchanging private key between service and iPhone app - digital signing

I need to do digital signing of my request data which will be sent to the server. My server sends distinct private keys to her clients after authentication and expects all responses to be digitally ...
2
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1answer
224 views

VKO GOST R 34.10-2001 (described in RFC4357), Key Agreement Algorithm. Looking for its implementation/detailed description/examples

VKO GOST R 34.10-2001 was described in RFC4357 Page 7 But the description is very poor. Here it is: This algorithm creates a key encryption key (KEK) using 64 bit UKM, the sender's private key, ...
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1answer
112 views

Help to understand the chameleon hash function?

Recently, I'm reading Non-Interactive Key Exchange, in the section 4.2(Towards a factoring-based scheme in the standard model,Page 10), the authors uses $$t\gets ChamH_{hk}(Z||ID;r);\\ Y\gets ...
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Quantum key exchange skepticism/confusion

I was hoping somebody could explain some issues I have with quantum key exchange that I don't quite understand. I've read bits and pieces about BB84 but I'm sure my questions probably apply to other ...
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1answer
149 views

Is encryption mainly using Diffie-Hellman Key Exchange?

I know how Diffie-Hellman Key Exchange works. Is this the main way of encrypting with PGP, ssh, ssl (https), DKIM, ...? I wonder if Diffie-Hellman is the clue to understand how encryption with ...
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42 views

Malicious KGC attack in the identity-based authenticated key exchange protocol

There are two users $A$ and $B$ who are in different domain. Let's assume that $A\in KGC_1$ and $B\in KGC_2$. If they want to establish secure session, then they must run an identity-based ...
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366 views

Problem with Python Implementation of Key Exchange part OTR Protocol

Being new to software development and crypto in general, I thought I would write a simple p2p encrypted chat app using the otr protocol detailed here: https://otr.cypherpunks.ca/Protocol-v3-4.0.0.html ...
2
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1answer
356 views

generate hash of all handshake messages for verify data (DTLS)

I am trying to create a DTLS client finished packet, where I need to generate verify data for handshake hash is need. And here I want to know how to generate handshake hash. As of now I am doing like ...
2
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1answer
68 views

TLS - sharing 1792 bits of unidirectional keys

I've just watched a video on the TLS protocol and learnt that it uses unidirectional keys (meaning keys for both sides, from browser to server and from server to browser). Given that the server uses ...
2
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1answer
78 views

Familiar key signing over video call

Say that a friend of mine and I have both generated new PGP keys, and we want to use a video call to verify each other's new keys because we live on opposite sides of the planet. While we could both ...
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2answers
249 views

Attack on a key-exchange,symmetric-key cryptography protocol

This is an exam question in Oxford 's Computer Security course: Here is the start of a protocol, based on a long-term secret key $k_{AB}$ previously shared between Alice and Bob, designed to offer ...
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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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Common pitfalls of session key activation?

Assume that initiator $I$ and responder $R$ of a key agreement protocol have agreed on new symmetric session keys $K'_{auth}$ and $K'_{enc}$, e.g. by way of Diffie-Hellman and key derivation, possibly ...