Questions tagged [key-exchange]

For questions relating to protocols for distributing public keys, and / or establishing session keys with another party. Examples of key exchange protocols include Diffie-Hellman and IKE.

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Which is better for SSL: TLS_EDH or TLS_SRP?

DH is vulnerable to a man-in-middle attack due to no server authentication; and RSA does not have forward secrecy. People suggest used Ephemeral DH but what are the differences between Ephemeral DH ...
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1answer
488 views

Any obvious flaws in this protocol?

Are there any particular flaws in this protocol? (Yes I know about SSL) Three participants: Login Server LS Game Server GS Client C Asymmetric key-pair Kpriv Kpub Shared 128bit secret key Ksec ...
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1answer
235 views

Inner Workings of Public Key Encryption

After watching this video explaining PKE with tennis balls (interesting), it left me with a few particular questions that I'm having trouble finding answers to: I assume that they keys used to unlock ...
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2answers
108 views

Is it a good idea to use asymmetric encryption for a chat application?

I am reading design documents of an internal Whats-app like chat application. Developers are planning to use asymmetric encryption to encrypt all messages. Every user will have a public/private key ...
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2answers
56 views

What is the message called someone sends to verify a key?

Suppose Alice wants to check if Bob has a certain keypair. Alice could send some random payload to Bob and let Bob sign that payload with his private key. Alice is now able to check if the signature ...
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3answers
3k views

Sharing Derived Unique Key Per Transaction (DUKPT) Base Derivation Key (BDK) with a partner

Assumptions: We have devices out in the field injected with keys derived from our one and only BDK. The devices encrypt data using the injected derived key. All our devices connect to our server ...
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2answers
1k views

Key distribution and key exchange for simple secure FTP implementation

I'm developing a simple secure file transfer protocol for a University project using openssl. I have a Client (let be C) and a Server (let be S). C will send to S messages like get, put, cd, … and S ...
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1answer
212 views

Mutual Anonymity in key exchange

If Alice (sender) sends a private message embedded with public key of the Bob(recipient) through onion network, so in this key exchange, does Bob remains anonymous to Alice as Alice knows about the ...
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3answers
2k views

Establish a secure channel with mutual authentication given pre-shared public keys

Suppose I have a system whereby parties are identified by their public key (with some pre-selected asymmetric key algorithm). Suppose I have a party PUB1 which wants to establish a secure channel with ...
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1answer
4k views

How to test TLS handshake process?

I need to test the handshake process of TLS. I thought to use inter-process communication in Linux. Is it possible or not? If not, what simulator could be used for this purpose? If yes, what do I ...
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1answer
252 views

Prevent padding oracle attack on key exchange process

I found in my searches that the padding oracle attack can be used against the RSA with PKCS1PAdding or OAEP padding, and I used this algorithm for a symmetric key exchange. How can I prevent a padding ...
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2answers
594 views

Does Ephemeral Diffie-Hellman require a certificate?

In Ephemeral Diffie-Hellman, the key pair is generated every time. In practice, does this mean I never need a certificate? Or that means I need a new cert every single time?
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3answers
254 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?
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1answer
79 views

Is this key exchange algorithm secure and valid? [closed]

I'm writing reliable UDP implementation and I want it to be secure. Also, I want to make use of elliptic curve cryptography. I don't have the proper education to really understand the math behind this ...
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1answer
249 views

ECDH and static key encryption

It's been a while and I'm still trying to figure out if my understanding of ECC crypto is correct. Basically from what I understood a purely asymmetric encryption is never used. Usually the ...
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1answer
728 views

Can you identify whether a string is a RSA public key?

I am generating RSA keys with the openssl library. I have heard that it is possible to recognise the method used to encrypt a string with AES or DES but is it possible to identify whether a string is ...
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1answer
476 views

Securing an SFTP server

I have been asked to secure an SFTP service and running a scan using nmap.exe --script ssh2-enum-algos <host> -p 22 returns the following: 22/tcp open ssh | ssh2-enum-algos: | ...
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2answers
137 views

Man-In-The-Middle (SSL) attack in my case

I am taking a course in a school about network security. In a experimental exercise, I was asked to install a Man-In-The-Middle (SSL) app to a mobile phone, and install a certificate(with private key ...
2
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1answer
248 views

Could Diffie-Hellman be used to stop people who knows the PSK from snooping on your WiFi?

One known problem with WPA2 is that anybody who knows the preshared key can snoop on the handshake and decrypt all subsequent traffic between any parties on the network. In the typical coffee shop ...
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1answer
606 views

Is Diffie-Hellman key exchange the best way to securely exchange SSH keys?

I'm designing the communication mechanism for end user devices that will communicate with a row of servers. My current plan is on first run, a device will generate its own SSH key pair (RSA and 4096 ...
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2answers
8k 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 hmac-...
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2answers
184 views

Can be used ECDH with static public key and parameters?

I have protocol required for privacy. Thus, I want to use hybrid cryptography. Base on my knowledge, ECDH is fast and secure. My system consists of 3 main components a trusted-server, client, and ...
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1answer
95 views

Secure Key Storage

We have a security solution that is deployed on premise to companies with big technical infrastructures. We do real time vulnerability/configuration assessment of all critical assets in the network. ...
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1answer
458 views

Limit on modulus lines in OpenSSH /etc/ssh/moduli file?

I understand that OpenSSH server looks in /etc/ssh/moduli and picks a modulus at random for each Diffie-Hellman group exchange. What I am wondering is whether there is a practical limit on how many ...
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1answer
486 views

Can an OpenPGP primary key revoke a subkey of a subkey?

I would like to have the following setup: a main Key, saved in a hardware wallet or paper wallet. Let's call this level 1. The idea is to never have to use this key again, as a sort of last resort. ...
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2answers
163 views

Can a user verify the quality/safety of pregenerated SSH moduli parameters?

Many tutorials about how to mitigate the Logjam recommend regenerating Diffie-Hellman moduli. This is a resource intensive operation, especially for high-bit groups. This made me think if it made ...
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1answer
289 views

Security of Web Game over WebSockets?

Project that I'm working on depends on WebSockets to communicate between the server and client browser for all interactions within the game. I'm attending university for Computer Security, but I'm ...
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1answer
96 views

Is there a PAKE algorithm where the passwords can be tested in the first round?

I want to use PAKE for key exchange between two parties (Alice and Bob) which share a low entropy secret (a password they exchanged on a piece of papers). Alice and Bob use a software on there ...
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3answers
331 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. ...
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1answer
410 views

Picking exponents for Diffie-Hellman

I'm taking a class on Cryptography and the professor mentioned that given mod N and base g with a certain order, you should pick powers m and n such that they create a certain property with the order ...
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0answers
401 views

computing the exchange hash for ecdsa-sha2-nistp256

I am writing code for an SSH server and can not get past the Elliptic Curve Diffie-Hellman Key Exchange Reply part of the connection. The client also closes the connection and says "Host Key does not ...
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3answers
139 views

How secure is using Saving Session Feature on WinSCP?

I ssh to my AWS instances via WinSCP and it has public-private key authentication, password authentication is disabled. All the sessions are saved on WinSCP, so I click on the IP of the machine and I ...
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136 views

Is it safe to retrieve GnuPG public/secret key with fs in Node.js?

So there is a Node.js package openpgp which is available for signing documents with GPG, but it requires public/secret key. We all know putting key right into the file is dangerous and not recommend ...
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2answers
5k views

How do certificates stop this man in the middle attack?

Alice and Bob are trying to set up a secure conversation, but unknown to them in the middle is Eve, who can intercept and modify all packets sent between them. The communication goes as follows: ...
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3answers
238 views

Cryptography key gathering tool [closed]

I am wondering if there exist a tools which can return the value of the one of the private key if the following are known: 1) Encryption Algorithm 2) Public key 3) Plain text 4) Cipher text Or may be ...
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3answers
242 views

Given a large enough sampling of public keys could one begin to identify a private key?

For example, an ISP or government capable of tracking millions of keys being exchanged. Would that provide a sample large enough to be able to identify the private key on either end?
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1answer
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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 ...
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1answer
907 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 ...
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2answers
404 views

How do key servers resolve conflicts?

According to the PGP network FAQ While a number of key servers exist, it is only necessary to send your key to one of them. The key server will take care of the job of sending your key to all other ...
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2answers
2k views

SSL / TLS Ciphersuites [closed]

There's a large list of ciphersuites inside SSL / TLS. It seems like that these ciphersuites can be categorized in terms of their underlying mechanism with following categories: RSA Key Exchange (e.g....
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1answer
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TLS 1.2 Handshake: How is the ECDHE public key signed by server?

I am dealing with a situation where a cipher option, such as ECDHE-ECDSA-AES128-SHA, is chosen for establishing a TLS connection. In this case, a server, when sending the ServerKeyExchange message to ...
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3answers
112 views

Are there any actual disadvantages to a key signing party?

At the beginning of the year staff are required to attend a key signing party - after changing their keys. They are required to bring said keys on USB sticks, at the end of the party each member of ...
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1answer
5k views

What is the the meaning of “out-of-band” in “out-of-band key exchange”?

When we say "out-of-band exchange of symmetric keys", what does "out-of-band" mean?
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4answers
371 views

Can an ssh key login to a secure remote server be compromised when on a network run by a bad actor

I am in a cafe. Supposing I ssh into a secure remote server using a key pair, and supposing the cafe wifi is run by a bad actor who is intercepting traffic, can my login be compromised? I am not ...
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1answer
126 views

Why is brute forcing DH private key harder than calculating public key?

Assuming shared parameters: prime p base g Alice's private key is a and her public key is A, which is g ^ a mod p Calcuating A requires g * g * g... a times. Modulus is applied whenever necessary. ...
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2answers
133 views

Combinations of key exchange and signature algorithm in TLS

Let's say that one does not trust ECC a lot, and values confidentiality over authenticity (perhaps simply for the reason that MitM is more difficult than passive eavesdropping and decryption later on)....
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1answer
188 views

Diffie Hellman and exchange of public key for signature

Let's assume an insecure channel. Is it safe to exchange Alice & Bob public keys first then apply them to sign communications during the DH process? (then encrypt+sign all future communications)? ...
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2answers
2k 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, ...
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1answer
3k 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 Enc=...
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1answer
3k 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 http://www.ecc-brainpool.org/...