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 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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57 views

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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1answer
72 views

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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48 views

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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56 views

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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1answer
59 views

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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106 views

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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1answer
98 views

Why is an ephemeral key required to prove possession of a static private key in Key-Establishment Schemes

In the NIST 800-56A rev3 "Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography" in section 5.6.2.2.3.2 "Recipient Obtains Assurance [of the ...
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How to calculate a common encryption key between sender and receiver

In the picture below, for the text underlined in red color: 7X(MOD 11) = 72(MOD 11) =49(MOD 11) My questions are: (1) obviously there is no equal relationship between 72(MOD 11) and 49 (MOD 11), and ...
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What can I use for key exchange?

I am trying to send AES keys from one computer to another, but I need to provide some form of attestation of the key's provenance. How should I go about doing this?
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CK vs BR Key Exchange Security Models

I'm writing a paper on Authenticated Key Exchange Protocols. I've read Bellare and Rogway's seminal paper on the subject and I think I understand BR Model and I'm now reading Cenetti and Krawczyk's ...
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What are the explicit usage of different keys derived from SKEYSEED in IKE?

We have seven different keys derived from DH key and nonces via PRF in IKEv2 as skd, skai, skar, skei, sker, skpi, skpr. Why different keys are generated for initator and responder for encryption? ...
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Why pre-shared key is not involved to key derivation in IKEv2?

In IKEv1 (RFC 2409), preshared secret is involved to key derivation where IKEv2 (RFC 7296) use it for only authentication. When we consider post-quantum security, this property makes IKEv1 suitable if ...
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SIDH: What if the two kernel generators are chosen in the same torsion group?

In SIDH, either party chooses its secret point $R_A = [m_A]P_A+[n_A]Q_A \in E[\ell_A^{e_A}]$, $R_B = [m_B]P_B+[n_B]Q_B \in E[\ell_B^{e_B}]$ from two different sets $E[\ell_A^{e_A}]$ and $E[\ell_B^{e_B}...
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When is a PQ key-exchange algorithm suitable for use with long-term static keys?

I took a look at Cloudflare Circl because I'm curious which Post-Quantum algorithms are implemented in Go, which could be used to exchange a key. I read this comment that SIDH is only good for ...
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Can Merkle signatures be leveraged for key exchange?

A Merkle signature scheme is post-quantum-suitable as it relies only on the security of a one-way function. However, this construction seems to only be capable of authentication, and not ...
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55 views

Under which conditions certificate is required for IKEv2?

In IKEv2 document, there are expressions as [CERT,] or [CERTREQ,] in the parts of IKE_SA_INIT or IKE_AUTH exchanges. In this notation brackets indicates that it is optional. I didn't see expressions ...
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Method to mitigate MitM attack for DH key exchange

Plain DH key exchange protocol is vulnerable to MitM attack. I checked the SRP (RFC 2945) but did not fully understand why it can help. I thought of a fix to mitigate MitM problem by using a pre-...
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Why do you need to apply hash over DH shared key? [duplicate]

I`ve read multiple times that it is not safe to use the shared key resulted from DH key exchange directly and that you need to do a KDF or hash over it and then use the result as a key. Why is it not ...
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59 views

How to decrypt raw TLS bytes?

Is there any tool / way to decrypt raw bytes of a TLS 1.2 session, when the master key is known, even if forward secrecy is used? The closest I found is this. I know its possible using Wireshark, but ...
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What is the simplest post-quantum asymmetric cryptographic algorithm for key exchange?

This question has been burning in the back of my head for the past few days, and a quick Google search doesn't yield any usable results. As the title suggests: What is the easiest-to-understand post-...
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Comparing Diffie Hellman and EC Diffie Hellman sizes

So, I am currently trying to understand the differences between DH and ECDH. I understand the basics between how the two algorithms work, however, I do not clearly understand how to compare the ...
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1answer
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Intuitive explanation for key exchange with public/private keys

I want to teach some people about crypto basics, and one of the topic will be key exchange with a public and private keys. The audience is made of people working in InfoSec, but mostly junior fresh ...
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1answer
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What does DH(IPKa, IPKb) notation mean? Diffie-Hellman confusion

I'm trying to implement X3DH (extended triple Diffie-Hellman) in a network of mine. The way I understand it, a bundle (IPKb,SPKb,OTKb) is retrieved by Alice from Bob, through the server, and using her ...
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Is the following PAKE protocol UC secure?

Consider the following (simplification of a) PAKE protocol: Alice and Bob start with a pre-agreed password pw. To establish a new session key $k$, first Alice samples a random nonce $r$ and sends it ...
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what motivated the design decisions of RFC 8291 ("Message Encryption for Web Push")?

Related question here. I'm reading RFC 8291, which describes a protocol to protect web push messages sent between an application server and a user agent (typically a mobile browser or other mobile ...
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Does IND-CPA to INC-CCA effects on the error probability?

If we have a key encapsulation mechanism (KEM) that is IND-CPA secure, with some error probability $P_e$ (probability that the shared keys are not equal). The goal is to use the Fujisaki-Okamoto ...
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AKE using Noise_NNpsk2 vs Noise_NKpsk2

I am working on an implementation based on the Disco library, which itself is based on Noise and strobe framework. The goal is to do bilaterally entity-authenticated key agreement with perfect forward ...
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How efficiently can an attacker forge parts of a fingerprint?

If two devices do not trust each other yet, you can't simply send the correct fingerprint across: you have to manually verify it. I am looking into the security of comparing only random parts of a ...
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Simple description of a multi-party fair exchange protocol with trusted third-party

Imagine Alice wants to sell a file with important information to Bob for money. The file must be encrypted, so nobody can eavesdrop. It must also be signed upfront, so Bob knows it has not been ...
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Is there any standard present to measure strength of a generated key using true random number generator?

I was wondering how to measure the security strength of a generated secret key for the below protocol: "A 128 bit random number is generated by TRNG and the random number will be used as a ...
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Finding Diffie-Hellman secret key with only some know values [closed]

I currently have the following information and I assume the first line separated by the: represents the prime number and generator. Is there any way I can find the secret key shared for the Diffie-...
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In group key agreement/exchange protocols, does key independence implies forward and backward secrecy?

Kim et al. [here] define Foward and Backward secrecy as follows: Forward Secrecy (not perfect foward secrecy): the inability for a passive attacker to obtain past group keys from a subset of new ...
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1answer
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What is the extra defense that McEliece 6960119 and 6688128 have that 8192128 does not?

From https://csrc.nist.gov/CSRC/media/Projects/post-quantum-cryptography/documents/round-3/official-comments/Classic-McEliece-round3-official-comment.pdf The 8192128 parameter set is bigger, but the ...
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Dragonfly masked DH

I was looking at Dragonfly key exchange protocol RFC 7664, and it seems to make use of masked Diffie-Hellman in the final part. Generating two random numbers less than group order $q$, $m$, and $r$ ...

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