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

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MTI authenticated key exchange protocol and their vulnerabilities?

Can someone please explain the different MTI key exchange protocols (A0, B0, C0, C1) and their vulnerabilities. I've been trying to read about them but couldn't get much information.
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2answers
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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
233 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
51 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
37 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
60 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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20 views

Run Diffie-Hellman in two processes [migrated]

I have the Diffie-Hellman code working properly but what I need is to run that program in two different processes (Say one process as Alice and another as Bob) and they must agree on the key sharing ...
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1answer
59 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
45 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
47 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
42 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
71 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
32 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
52 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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0answers
54 views

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
61 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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33 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
64 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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33 views

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
108 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 ...
3
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1answer
34 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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33 views

Is using Ed25519 key to generate DH key safe?

I want to know if it's safe to use ed25519 key pairs to generate a session key for message exchange.It works as follows: Assume Alice has ed25519 key pair $(A_{sk},A_{pk})$ and Bob has $(B_{sk},B_{pk}...
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1answer
62 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
78 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
40 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 ...
2
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1answer
39 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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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
51 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
48 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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47 views

Is this a good way of storing a symmetric encryption/decryption key?

I'm creating an Android app that enables users to send the following sensitive info to other users: Name, surname and email Current user location This information is sent by User A, encrypted using ...
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What pairing does Charm Library use, like Tate or Ate or something else?

I'm implementing a pairing-based key-agreement scheme using Charm Crypto and PBC, and I'm struggling to understand the relationship between the curves proposed for use with pairings and the pairings ...
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74 views

Which one counted as key freshness must be freshness in session or each message send

Which one means key freshness 1 or 2 on Key Exchange 1: Changing private key to recomputes a new common key in whole session 2: Changing private key to recomputes a new common key whenever you send ...
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1answer
35 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
53 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
35 views

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
80 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 ...
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3answers
122 views

Is perfect forward secrecy (PFS) possible without public key cryptography

I have an understanding of PFS as used in most key agreement algorithms as well as things like TextSecure protocol and ratchets. My undestanding is that PFS is not possible without asymmetric (public ...
2
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1answer
150 views

What is a 'known answer test' (KAT)?

Came across this concept on while reading up on the key-encapsulation protocol SIKE but haven't been able to find a good explanation of what a known answer test is formally. What is a known answer ...
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2answers
77 views

Multi-party key agreement

I have done a google search for "multi-party key agreement", and there doesn't seem to be anything more recent than about 2005. Are there any practical multi-party key agreement protocols known? ...
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39 views

Multi-party Key Exchange protocol from lattice

There are many two-party or three-party key exchange protocols from lattice. But, it seems that there is no famous multi-party key exchange protocol. Does anyone know the relevant knowledge? Or ...
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1answer
37 views

Charset of symmetric keys

I like to know from which charset a symmetric key is generated. Example: dm-crypt/LUKS The 128/256 bit (16/32 byte) key comes from /dev/urandom, and would be encoded as base64 string. So then I ...
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54 views

Where shoul I store private/public keys and how should I share it?

I'm new in terms of encryption and I have to encrypt the data between two Java Spring applications, one have serves as MVC framework and other as Web Service, I'm implementing an asymmetric encryption ...
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33 views

A modular approach to the design and analysis of authentication and key exchange protocols

I am studying modular approach to the design and analysis of authentication and of the key exchange protocols. One of them are proposed by bellare et al. On page number 11, I do not understand the ...
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0answers
48 views

Securing MQTT communication

I am building kinda simple IoT project, but I would like to implement good security (just for educational purposes and fun). My plan is to build simple solution where one arduino board reads some data ...
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1answer
54 views

correct a corrupted shared key

Suppose we have an almost shared secret. For example if we have a noisy connection to a shared secret source of randomness. So Alice has $k_1$ and Bob has $k_2$ similar but not necessarily identical ...
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113 views

ECC Curve25519: How to generate this kind of private key? / Strange key exchange mechanism

I'm currently reverse engineering a program that uses Curve25519 key exchange in network communication. I have only a basic understanding of ECC, so maybe this thing just seems strange to me. The ...
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1answer
37 views

Diffie Hellman Key Exchange Security wrt the hardness of discrete Logarithm

Hi I am very new to this field and I was wondering how one would prove or disprove the following statements: 1) if the DH key exchange protocol is secure for a finite cyclic group G, then computing ...
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0answers
37 views

Can “X3DH” instead of HMQV be used for OPAQUE?

So I recently re-read the OPAQUE paper and while reading it I found HMQV to be a bit "unnatural" / "unintuitive", which may just be because I didn't (yet) read the HMQV paper, so I wondered whether ...