Questions tagged [key-exchange]
Key exchange protocols allow two parties to produce a secret session key over a public channel.
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Burmester Desmedt confused on the last step
I try to implement in code the traditional burmester desmedt algorithm for group key agreement:
But I have the following question regarding the last step:
$K=k_{i-1}^{nx_i}K_i^{n-1}K_i+1^{n-2}\dots ...
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Why (N+1)sec's mDP Implementation does not check whether all the XORED received $z$ values are 0
In the original mDP protocol once all $z$ values received from each participant the following calculation is being done:
If either $XOR(z_1,z_2,...,z_n) = 0 $ or received invalid Signature then ...
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Which Auxiliary Hash Function to use for Pointcheval's mDP protocol
I study GKE+P group key agreement protocol presented on paper Flexible Group Key Exchange with On-Demand Computation of Subgroup Keys by Michel Abdalla, Céline Chevalier, Mark Manulis and David ...
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46 views
Sharing secret content with multiple recipients
I have a sender and N recipients, and am thinking of using the following scheme to send secret content to those recipients. This is similar context to a group chat or email.
I am no expert in crypto ...
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46 views
Simple but secure method to share secret (128 bit AES key) though an untrusted relay
I am creating an end-to-end encrypted group messenger, and am looking for a way for online members of the chat to a arrive at a shared secret that can be used as a cryptographic key. This will ...
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Security of the Needham-Schroeder public key protocol after a minor adjustment
I'm preparing for a computer security exam by going through some past paper questions. And I came across this particular one that I could not answer:
We have the Needham Schroeder Public Key Protocol:...
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2answers
404 views
Should we use IANA groups 14 (MODP), 25, and 26 (ECP)?
By looking at SonicWall Knowledge Base article Key exchange (DH) Groups Supported - Site to Site VPN:
It appears that our firewall supports DH group 25, and 26. Almost everywhere I've seen, they've ...
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Implememtning GKE+P Group Key agreement protocol on nodejs [migrated]
I try to implement the GKE+P protocol presented on paper Flexible Group Key Exchange with On-Demand Computation of Subgroup Keys by Michel Abdalla, Céline Chevalier, Mark Manulis and David Pointcheval ...
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Production Ready Message Format Standart for Key agreements on top of XMPP
Greedings,
I try to run group key agreements on top of XMPP thus I want somehow a production used message format for key agreement. As far I found theese:
XEP-0384: OMEMO Encryption
XEP-0102
But all ...
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1answer
75 views
Is OAEP needed when encrypting a session (random) key using RSA?
My question is two parts:
when encrypting a session key which is used to encrypt bulk data using a block cipher for example, is padding with OAEP really needed [i'm assuming the key is generated ...
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2answers
73 views
Is it possible to get different plaintexts from a single ciphertext using different keys?
Suppose to have a chipertext that you can't decrypt, but you know that the plaintext can be A, B or C. Then arrives to you the key which is used to encrypt the chipertext.
You can decrypt the ...
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1answer
109 views
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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1answer
120 views
How does Dragonfly key exchange work, in non-white-paper terms?
I'm trying to understand WPA3, whose Simultaneous Authentication of Equals is supposedly similar to Dragonfly Key Exchange.
Dragonfly is resistant to dictionary attacks, meaning that rather than an ...
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1answer
56 views
Why does DH-EKE require that public keys be indistinguishable from random?
The introduction to SPAKE pre-authentication states:
Diffie-Hellman Encrypted Key Exchange (DH-EKE) is the earliest widely deployed PAKE. It works by encrypting the public keys of a Diffie-Hellman ...
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1answer
93 views
In a TLS 1.3 connection, how do the client and server choose a mutual cipher suite?
According to KeyCDN, TLSv1.3 connections are established in a single round trip:
While TLS 1.2 requires two round-trips to complete the TLS handshake, 1.3 gets the job done in just one trip
If ...
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1answer
31 views
Verion of crypto_box() which doesn't allow the sender to decrypt previously sent messages
Libsodium's crypto_box() family of functions allow the sender to send messages using its public/private keypair knowing the receiver's public key, and allow the ...
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Simulatability of Diffie-Hellman Key Exchange
While reading through Shoup's paper on provably secure Diffie-Hellman key exchange (DHKE), I do not understand something rather simple.
There are two parties $A$ and $B$. $A$ starts by sending $g^a$, ...
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2answers
80 views
Curve25519 Key Exchange Bit Security
Please note I am new to Cryptography in general. Sorry if I do not use the correct terminology/my question has some fundamental flaw.
Alice and Bob want to communicate securely over an insecure ...
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2answers
290 views
Do standalone Oblivious Transfer (OT) Protocols exist?
Are there any Oblivious Transfer (OT) protocols that don’t rely on asymmetrical encryption, public-key encryption or key-exchange?
I’m starting to wonder, as all the OT protocols I know of (and can ...
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1answer
87 views
How to handle a lost key in Diffie-Hellman Key Exchange
I implemented the Diffie-Hellman Key Exchange algorithm but, I was wondering how to handle if one of the parties lost his key.
Let's take a chat app as an example, Bob and Alice they used to have a ...
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1answer
73 views
Asynchronous Ratcheting Tree and modern group key agreements: Why left balanced-tres used?
Nowadays the group key agreements are based upon tree-based ones such as Asynchronous Ratcheting tree. Especially the latter one is constructed upon left-balanced tree.
So I keep wondering what ...
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1answer
68 views
Change a secret key in an embedded device
There is a device that uses a secret key Sk to encrypt data.
Assume this Sk is compromised.
Could the following scheme be considered safe, in case we want to change the compromised Sk:
We store some ...
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1answer
64 views
How to exchange a secret through untrusted server in two steps?
I have a web application where I control the server, however, it should not have any knowledge of secrets that are exchanged between its users. This server holds RSA public keys of each registered ...
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1answer
75 views
Publicly exchanging keys
my use case is the following: Sharing a secret on the blockchain from one participant over a smart-contracts with revealing the secret only after some condition is verified (another participant has ...
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2answers
61 views
Does the Server Key Exchange sign a hash or text
In TLS 1.2 when using ECDHE_RSA, the ServerKeyExchange message contains a signature over the server's ECDHE public parameters. My question is: Is the signature over ...
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1answer
57 views
Why are computations (isogeny) in SIDH done in an extended prime field?
While reading the SIDH key exchange protocol, I noticed that all the isogeny computations and curves are defined over the extended prime field $\mathbb{F}_{p^2}$. Does it make the problem ...
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Asyncronous Rachet tree: How user movability is handled is the Rachet tree being recreated?
As I have read the latest state of art in group key agreement is the Asyncronous Rachet Tree.
But in applications like IRC that exists high user movability (users join in ans leave the room). Is ...
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1answer
80 views
How Elliptic-Curve affects the Server Key Exchange parameters
In Finite Field DHE, the server sends the following parameters in the server key exchange message:
$p$: prime
$g$: group
$g^b$: the server's public DH key
In DHE_RSA (non anonymous DHE), the server ...
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1answer
35 views
mDP kay agreement protocol where z's are found on the step where the common key is generated?
Whilst I was studying the mDP protocol I came across into the following step:
Group Key agreement:
Each $U_i$ checks whether $z_1 \bigoplus ... \bigoplus z_n = 0$ and whether all signatures $\...
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1answer
55 views
Key exchange protocols non-reducible to groups
Some questions I have ended up wondering about while reading through many of key-exchange protocols are:
Is there an intrinsic reason, why most key exchange protocols use group-based approaches apart ...
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IND-CCA2 post-quantum key exchange
QUIC requires that servers reuse keys so that session resumption works. That breaks many post-quantum key exchange systems.
I am looking for a post-quantum key exchange algorithm with the following ...
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Signal Sender Keys: Why it works and which is the common key at the end?
As I has read upon "WhatsUp Encryption Overview" when a client receives a sender message then it performs the following actions:
Decomposes Sender Message to ...
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1answer
77 views
Tls protocols: is the simple diffie hellman key exchange still used these days?
Or did it mostly get replaced by ecdh for key exchange and rsa for authentication ?
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0answers
35 views
Proving the lack of Perfect Forward Secrecy
In specific regarding the NSA's Key Exchange Algorithm, I read in an analysis of the protocol that perfect forward secrecy cannot be provided.
Is there any way to prove or justify this? I couldn't ...
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1answer
106 views
Post-quantum X3DH
I was trying to look into weather or not it would be possible to build a post-quantum version of the signal protocol. The double ratchet algorithm is trivial to modify, replacing the ECDH key ...
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Are there any key exchange algorithms with high failure rates (i.e. Alice and Bob often have to try multiple times to establish a common key)?
I am wondering if there are any key exchange algorithms which have a very high failure rate in the sense that there is in the neighborhood of a 50 percent change or so of establishing a common key per ...
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2answers
116 views
challenges in quantum key distribution
Quantum key distribution (QKD) promises unconditional security in data communication and is currently being deployed in commercial applications. Nonetheless, before QKD can be widely adopted, it faces ...
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1answer
54 views
Secure password-authenticated key exchange that allows for passwords to be stored as hashes, but does not make the hashes password-equivalent
Are there any secure password-authenticated key exchange that allows for passwords to be stored as hashes, but does not make the hashes password-equivalent? This would be useful for many ...
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1answer
65 views
Why use a date-dependent substring of a pre-shared key instead of just the key?
I've recently come across a situation where one system passes an encrypted payload to another system. The payload is encrypted using a pre-shared key. However, instead of just using the key itself, a ...
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2answers
94 views
Multiparty key exchange for end-to-end encryption
I need to make end-to-end encrypted messaging between 2 and more parties without trusting a server. Each party has it's secret and private keys. The obvious solution is to make ECDH between all of ...
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1answer
48 views
Signal/TextSecure multiparty Chat. Does the protocol transmits a symmetric key?
As I look over the TexSecures specifications for multi-party chat I have noticed this. Also as far as I understood in TextSecure (now known as Signal) the minimal steps required to do a secure ...
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1answer
47 views
Does a key exchange protocol with mutual authentication which does not provide forward secrecy can be proven secure in Bellare-Rogway model?
Is forward secrecy a necessary security property for a AKE protocol to be proven secure in Bellare-Rogway model? Is freshness also a necessary security property for a AKE protocol to be proven secure ...
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0answers
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Nature of risk(s) from KeeChallenge XML file stored in cloud at Onedrive
As a noob user of KeePass2 on Windows desktop and Keypass2Android on my phone, supplemented by YubiKey Neo configured for hmac-sha1 challenge response, I noticed that Keepass2Android appears to store ...
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0answers
77 views
Multi-Party Offline Key Exchange Using Public and Private Keys
I hope the title already explains the problem I have in mind; but let me lay out some more details.
Given public-private key pairs $P_A, P_B, P_C, ... P_Z$, (first $3$ of which are owned by our usual ...
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1answer
38 views
what can attackers do between two end hosts
I have one question that I couldn't come up with a nice solution.
So let's have this analogy, I have a box full of money and I want to deliver to this my friend. Here if we think of a potential ...
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1answer
84 views
What are the differences between ephemeral-static ECDH and static-static ECDH?
As I know ECDH can be used with a fixed public key. I read there are two types of static ECDH, ephemeral-static ECDH, and static-static ECDH.
What are the differences between these two types?
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1answer
38 views
How does hill cipher key exchange takes place?
I am giving a presentation in my college where hill cipher is a part of the presentation. I just wanted to know, how is the hill cipher key matrix is exchanged securely in order to decrypt the message?...
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0answers
61 views
How many qbits are required to break Diffie-Hellman over a multiplicative group
There have been comparisons between RSA and ECDH with regards to the number of qbits (qubits) required to break the algorithm with a specific key size. But how many qbits are required to break "...
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0answers
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Key update and re-keying
What is the exact difference between the key update and re-keying? Following the discussions here, I understood that the key update is the process of deriving the new session key from old key. In the ...
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1answer
93 views
How do applications set up secure communications through an untrusted middleman?
I recently discovered Tox whilst looking for alternatives to Skype, and while the Tech FAQ goes into some details about algorithms used, etc. I don't understand how keys are securely exchanged.
I ...
