for questions relating to key exchange protocols.

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10
votes
1answer
4k views

How does SSH use both RSA and Diffie-Hellman?

SSH protocol 2 allows you to use DSA, ECDSA, ED25519 and RSA keys when establishing a secure connection to a server. (Keep in mind for this question that I'm only familiar with the procedure and ...
2
votes
3answers
243 views

Why do I have to use multiple keys for each direction and purpose?

I'm currently writing an examen about 'Lessons Learned in the IT-Security'. I already found some thing, which shouldn't be done. But right now I'm in trouble finding the reasons why not to do so. ...
3
votes
1answer
151 views

What is 0xXXXXXXXX.asc.sig and how can I generate this?

When I am exchanging PGP keys with someone, I receive the regular 0xXXXXXXXX.asc file and regularly receive a file called 0xXXXXXXXX.asc.sig. What is this file? How can I generate one and send it ...
0
votes
1answer
191 views

Why do we encrypt ephemeral Public key in Encrypted Key Exchange

Encrypted Key Exchange can resist off-line dictionary attack Protocol : A ---> B : Ep (PK) B ---> A : Ep(Epk(K)) K is Session Key generated by B PK is an ephemeral public key ...
1
vote
1answer
651 views

Authenticated Diffie Hellman Key Exchange

It appears that the textbook version of Diffie-Hellman is susceptible to man in the middle attack and the use of digital signatures could prevent this attack from occurring. Digital signatures could ...
0
votes
1answer
138 views

How could SSL certificate affect the symmetric key length?

This article in GoDaddy support knowledge base says All of our SSL certificates support high-grade 256-bit encryption How would they not support it? The SSL certificate contains keys for ...
0
votes
1answer
191 views

Key Exchange using RSA

I'm trying to do key exchange using the following scheme. Server generates an RSA-2048 key pair and sends the public part to the client Client generates an RSA-592 key pair (I have to use RSA-592 ...
1
vote
0answers
75 views

Verifying the owner of a signing key

I'm using elliptic curve cryptography (curve25519 and ed25519) for key exchange and signing. The signing and key exchange keypairs are independent. I need two users to be able to verify each other's ...
0
votes
1answer
999 views

rolling code & keyless entry system [closed]

The security industry typically uses rolling code algorithms to authenticate sender & receivers in keyless entry systems, which is called RKE (ex: KeeLoq). In key-less smart key car system, The ...
3
votes
2answers
7k views

Client-server encryption technique explanation (TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 128 bit keys)

I opened a web page using https. When I looked at the page info provided by my browser (Firefox) I saw following: Connection encrypted: High-grade Encryption ...
2
votes
2answers
117 views

Preventing a Computational DoS Attack in Public Key Cryptosystems

I'm designing a server which accepts anonymous messages using ECIES: as in, anonymous users send the server an ephemeral EC public key, and the server uses ECDH to derive a shared secret, and some KDF ...
0
votes
1answer
154 views

How can I generate some public and private keys on both sides with low overhead?

We have an Authority Center (CA) generating some public and private keys for each client (more than one pair for each client). One method for sending keys to client is sharing a secret key between CA ...
0
votes
1answer
85 views

MITM protection, key distribution

I want to make sure each of my apps users only get their own data, and that nobody tampers with it or sniffs it in a MITM fashion. Encryption of everything should be the solution, right? But how do I ...
1
vote
2answers
304 views

What are the alternatives to ECDSA for an authentication protocol?

In an authentication protocol, S has a public/private key pair known to C, and S and C have established a secure channel (for example, using DH or ECDH, or any other key exchange protocol). C wishes ...
3
votes
1answer
47 views

Transferring of keys from key servers to recipients

When I download PGP keys from keyservers like so: gpg --search-keys steve@openssl.org How are the public keys transferred down to my machine? Is there a possibility of a MITM attack to serve me the ...
4
votes
2answers
118 views

How to establish a random OTR remote party as a specific individual?

In reading Glenn Greenwald's 2014 book No place to hide, one thing stood out to me as a bit odd. Greenwald details how Edward Snowden was insistent that Greenwald install PGP in order to communicate ...
4
votes
1answer
909 views

Diffie-Hellman key exchange

The following image attempts to explain the diffie-hellman key exchange for people not strong in maths such as myself: I do understand how the colour/paint example illustrates the idea. But I'm a ...
0
votes
1answer
245 views

In IKE protocol; what is the PRF? [duplicate]

In IKE protocol; what is the PRF ? What is "the generation of a key based on modeled random oracle hash functions"?
1
vote
0answers
263 views

SSH using pre-existing session (symmetric) keys

Is there at present a way to open a SSH connection using pre-existing symmetric session keys? In other words, if I create a list of symmetric keys can I send that list to the recipient on a CD or USB ...
0
votes
2answers
173 views

Is it safe to use a ECDSA public key as a password seed for GCM/AES?

Two peers already exchanged their ECDSA (curve secp256k1) public keys using a secure channel. They want to establish an authenticated encrypted channel between them. They will use CCM mode and with ...
12
votes
1answer
6k views

What are the OpenSSL standard Diffie Hellmann parameters (primes)?

I recently generated some custom Diffie Hellmann parameters which are basically just long (in the below case 4096 bit) primes. Those are then used in the key exchange process. I used the following ...
1
vote
1answer
67 views

Evaluation of cryptosystem for authentication and keyexchange

I'm a masters student in computer science who works part time with my own company as a consultant. My lastest project is based on my bachelor thesis which handles everything except the security. The ...
0
votes
1answer
923 views

Is the Station-to-Station protocol secure?

After I've read a lot about key exchange many sources state that the Station-to-Station is secure, since it also verifies the entity on the other side. Well how is that true, if an active Man in the ...
18
votes
9answers
3k views

Are there any systems out there that use a one-time pad?

I'm still new to information security, but I have read a bit about the one-time pad. The point that sticks out to me the most is that it is supposedly unbreakable. Has this method of encryption ever ...
1
vote
2answers
979 views

SSL/TLS : Authentication mechanism

I have these doubts regarding authentication in SSL/TLS : Will there be an authentication involved for all SSL connections ? For eg. when I browse the internet, using the most up-to-date browser, ...
1
vote
2answers
885 views

GSM A5/1 encryption: Key management

I'm currently studying the A5/1 algorithm used for GSM encryption. I understood how thanks to the symmetric private Key and a public counter frame one can encrypt the communication between A and B. ...
2
votes
3answers
171 views

Is it a good practice to include a download URL of my GPG public key in my email signature?

I was wondering if I can put a download URL for my recipients to get my GPG public key easily in my email signature. Is this a good practice? If not, what's a good alternative?
1
vote
1answer
3k views

Which is better in “DH-group14-sha1 with hmac-sha2-256” and “DH-group-exchange-sha256 with hmac-sha2-256” from performance and security perspective?

In our product (embedded system), so far we were using diffie-hellman-group1-sha1 with hmac-sha1. But due to security concern we are planning to use diffie-hellman-group14 for key exchange and ...
1
vote
3answers
413 views

Is a Diffie Hellman Ephemeral key good material for being used as a symmetric cipher algorithm key?

I am designing a secure protocol (for academic/learning purposes) and I am at the point where I need to (re)design the key exchange step. In my previous implementation, I used to rely on RSA to ...
1
vote
2answers
779 views

How to treat/hash ECDH shared secret to use as keys for AES?

I'm doing some studies/development for a security system that would use ECDH with ephemeral keys. In my code I'm currently using a 256-bit EC, so when the two parts compute the shared secret, I get a ...
1
vote
0answers
196 views

Does Diffie-Hellmann (DH) key exchange protocol lower Off-The-Record protocol (OTR) security level?

Off-the-Record protocol employes Diffie-Hellman key exchange protocol (DH). DH protocol does not provide authentication of the communicating parties and, according to many sources, is vulnerable to ...
0
votes
1answer
190 views

Key-Exchange Algorithms VS Local Key Generation?

I was wondering the difference in term of Security, Computational cost and Network overhead between the use of : A Key-Exchange Algorithm (e.g. Diffie–Hellman) to set up a symmetric key. The ...
1
vote
1answer
2k views

Can you generate Diffie-Hellman parameters quickly [closed]

I am working on an android project for school and I am supposed to do a DHKE(Diffie Hellman Key Exchange). Everything works well, the problem is that it takes a lot of time (really a lot) to generate ...
3
votes
1answer
208 views

Can we build a key exchange protocol without certificates?

Assume that the server and the client both has some secret key K. Is it possible to have a key exchange protocol with authentication between them such that MITM attack cannot hold and if the key is ...
3
votes
2answers
2k views

Why should the dh keylength match rsa length in tls?

A few sources state that the DH keylength (bits of the prime) should match the keylength of rsa for TLS. For example SSL_set_tmp_dh(3) from openssl has example code on how to match the dh parameters ...
0
votes
1answer
106 views

Key Exchange algorithm to be used for REST framework

I was required to create key exchange module for custom Rest framework which supports document level security in REST requests. Framework has its own security module which allows to encrypt parameter ...
0
votes
2answers
91 views

does a public key work with all encrypted programs

let us say, I use program "x" for my e-mail security. through them I have a public key and a private key. My friend uses program "y" for their e-mail security and consequentially have a public key ...
3
votes
7answers
344 views

How would I give an encryption key to only one person?

Let's say I have an encrypted message. I want to make it so that someone is able to decrypt it. The only way of giving it to them is online. For the purposes of this question, I can't call, mail or ...
8
votes
2answers
4k views

What is the difference between DHE and ECDH?

I learned that perfect forward secrecy is implemented through DHE and ECDH but what is the difference between these 2 key exchanges? Also can someone explain how perfect forward secrecy works? I've ...
6
votes
1answer
3k views

How to secure API (private key) for mobile apps

I am building a web service that has to be only accessible for iOS apps. In the future I want to expand to a mobile website to make my service also available for other mobile operating systems. Now, ...
0
votes
3answers
298 views

What are the MitM implications of a stolen client-side private key?

Many VoIP handsets support client-side SSL authentication for auto-provisioning. Unfortunately, some devices must be programmed with their client-side keys. (Keys generated on low-entropy devices are ...
87
votes
6answers
54k views

“Diffie-Hellman Key Exchange” in plain English

Can someone explain to me what is Diffie-Hellman Key Exchange in plain English? I have read in a non-tech news page that twitter has just implemented this technology which allows two persons to ...
3
votes
0answers
152 views

Main difference between Yahalom and Needham-Schroeder key exchange protocols

I am just wondering what is the main difference between the Yahalom and Needham-Schroeder key exchange protocols? Which protocol uses less computational power?
1
vote
0answers
61 views

Any Suggestion Exchanging shared key between process via port in untrusted machine (infected my malware)?

I am trying to get shared key between Firefox extension and a java program running in same machine. I am communicating both application via socket. My assumption is that malware is running in ...
4
votes
2answers
240 views

Purpose of key confirmation

Among the requirements for a secure key exchange is the key confirmation. I wonder why is this step required. Even if the other party hasn't computed a correct value for the shared secret, it doesn't ...
1
vote
1answer
2k views

Why Qualys SSL Server Test is giving me 80 and not 100 in Key Exchange?

My openssl ciphers -v 'CIPHER' output is the following: ECDHE-ECDSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AESGCM(256) Mac=AEAD ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA ...
5
votes
2answers
2k views

Website: Pre-Shared-Key Authentication

We have this web-application with high valuable (business) data. All communication is encrypted through TLS/SSL. While I consider this a really safe protocol, it can still be compromised if someone ...
1
vote
1answer
2k views

ECC Brainpool Standard Curves and Curve Generation with Bouncy Castle which seed to use?

I want to implement a ECC Key Agreement with a Brainpool curve brainpoolP512r1 or brainpoolP512t1. I'm not clear about whichseed value to use (and how). In this document ...
4
votes
1answer
3k views

How do I share my S/MIME public key?

I have setup S/MIME encryption for my email address, and I'd like to allow people to download the public key from my website, rather than having to first receive an email from me. I want the public ...
3
votes
1answer
544 views

Encryption key exchange for Tor

I've been studying how Tor works - including the great QA "Why can a Tor exit node decrypt data, but not the entry node?". I understand the concept of onion routing and multiple layers of ...