Questions tagged [key-exchange]

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

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Is libsodium's Key Exchange system secure?

I'm building a project using libsodium's AEAD + Key Exchange system and want to write a proof justifying the security of the project. I am wondering if I can find a source detailing the exact security ...
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What is stored in a register method using the OPAQUE protocol?

I am currently studying OPAQUE, and have no prior deep experience with cryptography. I am currently trying to develop a login/register system using OPAQUE for the authentication process. Should I ...
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How to extract an AES key which resides in a TR-31 keyblock

I have a version D TR-31 keyblock (which contains an AES Key for use in CMAC), and have the ZCMK key used, what is the method which I can use to extract the key from the TR-31 keyblock? I'll do my own ...
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Confirmation of receipt during the fair exchange

Is there a way to confirm the delivery of an item to the recipient e.g(bank payment)? Let's say there is a trust third party in the protocol. The sender's side (honest) says that it sent the payment, ...
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Are Encryption, Key Exchanges and Digital Signature the application of asymmetric encryption

Reading the wikipedia entry on asymmetric cryptography, will I be wrong to conclude that there are 3 main broad category of application for asymmetric cryptography? Mainly: encryption digital ...
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Need to know the key exchange value of the following cipher suites

I need to know the key exchange of the DHE-DSS cipher suites, will it be the same as mentioned in DHE-RSA?
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Sending encrypted message without public key from recipient (elgamal)

assume Bob and Alice use Elgamal encryption scheme. Alice wants to send Bob a message, but does not know Bobs public key. Is there a way for Alice to find out Bobs public key by receiving multiple ...
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Can a MITM during Diffie-Hellman key exchange manipulate both sides to generate symmetric secrets?

Is it possible for an attacker on a Diffie-Hellman key exchange to manipulate both sides in a way so that the secret generated on each side is identical? Or put differently, would it be possible to ...
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Key distribution protocol involves only 2 parties, given E[k1,E(k2,m)]=E[k2, E(k1, m)]

Given an one-key cipher such that: E[k1,E(k2,m)]=E[k2, E(k1, m)] Is there any key distribution protocol that involves only two parties (Alice and Bob) without the key distribution center? The protocol ...
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Sharing RSA private keys using key exchange algorithms like Diffie–Hellman Algorithm?

Me and my friend would like to login to an SSH server using the same private RSA key. However, we don't want to transmit the key over the internet, for security. I am thinking if it's possible to ...
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Curve448 - Can Ed448 key material be reused for X448?

Currently I am facing a situation in which Ed448 key pairs (private + public key) are available and the system should be extended by a Diffie-Hellman (ECDH) operation. First of let me summarize what I ...
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Comparing the performance of ECC/RSA with post quantum protocols

I wanted to compare the performance of different cryptographic systems. There is a pretty good paper comparing the 3rd round finalists of the NIST competition. I was wondering if there are good ...
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Can Bob and Alice do an authenticated Diffie–Hellman key exchange if Bob only knows the hashsum of Alice's key?

Tor vanilla bridges look like this: Bridge x.x.x.x:1234 9DD03662B50FEDBF6F8D5630CB86D7E8CE4F4432 It's only the IP/Port and a hash of the key. Can Bob and Alice do an authenticated Diffie–Hellman key ...
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Authenticated Diffie-Hellman with no proofs that each one keys are the right keys. Is it possible?

Let's suppose that Bob has only Alice's IP and no more information about Alice's key, nor the digest of Alice's key. They exchange keys and need proof that the received keys are the same keys that ...
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Tree Parity Machines (neural cryptography) advantages

It seems that neural cryptography is an interesting research topic and there are some important contributions published in the last years. The proposed algorithms are suitable for symmetric key ...
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Developing a Simmetric Key Distribution protocol to use with rfc6238

I'm trying to develop a Key Distribution Protocol to share symmetric keys in RFC 6238 (OTP). I started with RFC 6063, but this protocol is developed over old and known insecure algorithms like PBKDF ...
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Is the combination of X25519 ECDH and NTRU in OpenSSH 9.X secure against quantum attacks?

Can the combination of X25519 ECDH and NTRU in OpenSSH 9.X defend me against quantum attacks? Why is it believed that this combination is secure?
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Is there a standardized way to evaluate the security of a key exchange algorithm?

I'm now trying to design a more secure key-change algorithm to replace widely used DH. However, I am only able to prove that my algorithm is more secure logically, which means I can only prove it from ...
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Message Hiding Using Keyed Steganography

i would like to know what are the danger can be occur by performing steganography without a key? Please kindly explain to me.
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If the symmetric key is stolen; can I key revoke without reencrypted data?

I have a question about database security. This is a scenario I have. The data is encrypted using symmetric (i.e., AES) and stored in a database, while the secret key is stored on the client side, so ...
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Proving identity in asymmetrically encrypted communication

Let's assume such a scenario. Person A will broadcast his public key and person B will broadcast his public key. They can now communicate. But let's say that suddenly another person C will write to ...
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How are keys shared safely for block / stream encryption?

I've picked up a grad level computer security class. I read a brief overview on block and stream encryption. I understand and have used PGP in the past and it make since to share your public key. ...
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How to understand "Test() query can only be issued to a fresh session" in game-based security proof?

In game-based security proof for key-exchange protocols, there is a Test query. The Test(U) query typically is only available to the adversary if the attacked instance U is fresh. (U represents either ...
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Proof of score in a public game with a public contract leaderboard

Game: Users stack blocks to form an unstable tower. Each time a new block is successfully laid, the game creates a score_string which is meant as proof of the user's current score. Assume each user ...
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The Responsibility of Key Exchange

I've been implementing an asymmetric key exchange for creating a symmetric key. My question is more of a philosophical/legal one in terms of key-exchange responsibility, and what happens when let's ...
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What is the difference between key exchange protocol and key distribution protocol? [duplicate]

Can someone please explain what exactly is the difference between key exchange protocol and key distribution protocol? I looked on the Internet but it was not clear to me. I would be grateful if ...
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How can I use a secret sharing scheme when the secret is not a number but a statement?

I want to use a secret sharing scheme, where every player $i\in N$ has to share a pair of secrets $(l_i,\nu_{l_i})$, where $l_i$ is a unique code (positive integer) for every player, but $\nu_{l_i}$ ...
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ECDHE without initial handshake

Is it possible to do a key agreement with ECDH ephemeral-ephemeral without requiring an initial handshake first? Is it possible to have the key agreement in the same message as the encrypted data with ...
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How can I dentify the ECDHE group value used in a TLS session

In ECDHE, the group is a public value. I want to get this value for a session. I inspected the session using Wireshark. Under the ServerHello -> Key share extension -> Key share entry, I found ...
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Is the Key Exchange authenticated and confidential?

I have made a private messaging program and would like to check that nothing is stupid in my use of cryptography. I am an amateur and nothing is for production. I thank you in advance. The message ...
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Deterministic key selection using iterative value comparison - how dumb was this?

Just to start, this is mainly a curiosity question that's been nagging me for a while. I did a fair bit of googling to see if someone has already performed a righteous expose of this silly idea, but ...
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How are the cipher, the key and the initial message (that is not encrypted) are releted?

Suppose that $m$ is a message that someone player $i$ wants to send to a network of other players $j\neq -i$. The player to prevent his message from cheating by others uses an encyrpstion scheme. Say $...
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How to use ffdhe2048 in node js?

I am reading about Diffie Hellman key exchange from Real World Cryptography book and came across this For this reason, best practice nowadays is to use RFC 7919, which defines several groups of ...
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Is it secure to use RSA to exchange AES key?

I have to create a Client-Server Application using Java and I want to make the communication secure. I thought to use AES to encrypt the messages and for key exchange I make the next steps: Client ...
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Asymmetrically encrypt a short message into a short string

I have a string whose size is < 32 characters from the following limited character set. uppercase and lowercase Latin letters: A to Z and a to z digits: ...
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Where can I find good practice questions for proofs by reduction?

I already have the Katz-Lindell textbook, but I also want some additional practice problems for security reductions for stuff like PRFs, MACs, digital signatures, private and public key schemes, and ...
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*-LWE equivalent of Diffie-Hellman $g^{x^2}$ vulnerability

In Is Diffie-Hellman less secure when A and B select the same random number? , the possibility of Diffie-Hellman key exchange producing identical peer keys and the vulnerability of it against passive ...
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Encrypted data sharing in decentralised system

Alice encrypts file using her public key and upload it to decentralised file store (some service). Bob buys access to the file. Is it possible to share decrypted file with Bob without having Alice's ...
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Is Diffie-Hellman less secure when A and B select the same random number? [duplicate]

I understand that it is feasibly impossible for A and B to select the same random number, given the large input space, but what if it does happen? Does it effect the security of the key exchange? Can ...
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How to interpret my professor's statement about "seed" and "symmetric-key encryption"?

In the cryptography course, the professor said that: these days for symmetric key encryption, instead of sending out the key, Alice sends the seed to Bob, and then based on that Bob can get the key. ...
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Simple Key Exchange, One Server

I am trying to better understand how TLS works. I understand in the normal use case you need various random values generated and used in the key exchange, to prevent some MITM reusing a previous ...
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Are all public key a result of computing g^k mod p

I just read through the text book definition of Diffie–Hellman key exchange. And from what i understand, the public key that is shared based on the protocol is calculated from: ...
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X3DH and key exchange between Alice identity key and Bob pre signed key (DH1)

I'm getting familiar with Signal key exchange phase and as far as I understand all 3 exchanges between Alice ephemeral key and all of Bob keys from the bundle, I have some thoughts about key exchange ...
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SSL/TLS Forward secrecy with 2 KEM public keys

As we know, NIST PQC project is at its 3rd round, with draft standard expected to arrive in the next (few) year(s). An unfortunate fact is that, we're not seeing many signature schemes general-purpose ...
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Fast key exchange algorithm in hardware with small key size

Which asymmetric algorithm will be best only for key exchange to set up communication using symmetric cryptographic algorithm. Comparison should be in term of speed, key length and their hardware ...
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Combining Post-Quantum and Classical KEM

I came across this paper "Hybrid Key Encapsulation Mechanisms", were three methods are defined that allow a secure combination of a classical key encapsulation with a post-quantum key ...
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Secret sharing such that all shareholders obtain access to the secret (one shareholder can't just run off with the shares)

Say, using something like Shamir's polynomial scheme, you split a secret $x$ among $n$ people (each given a "share" of the secret) such that you need all $n$ shares to recover the secret. ...
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A source of randomness that anyone can independently, conveniently and robustly access?

Does there exist a source of randomness that anyone in the world can independently, conveniently and robustly access? For example, the 10th decimal place of the temperature in Mexico City is ...
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Verifying result of (EC-)Diffie-Hellman

I received a public key by JSON. For the example, I have 4 keys: 2 public keys and 2 private keys. ...
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XDH vs DH and ECDSA vs EDDSA

I am new to security area. I came across mutiple words I can't understand and there is little infomration I can get from google. What is XDH/XEC, is the X means 'enhanced'? Are they just have a ...
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