Diffie-Hellman is a method for establishing a shared secret that can be used as a cryptographic key.

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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 ...
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1answer
54 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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749 views

Relationship between RSA, Diffie-Hellman Key Exchange, PKI and X.509?

I am getting confused with RSA, Diffie-Hellman Key Exchange, PKI and X.509v3. I took a look of RSA's mathematics algorithm, it seems like a encryption algorithm, right? Generating public key and ...
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2answers
107 views

Extract pre-master keys from an OpenSSL application

Consider an application using OpenSSL which has a bug. A packet capture of the full SSL session is available, as well as a core dump and debugging symbols for the application and libraries. A RSA ...
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308 views

OpenSSL vulnerability CVE-2015-0205

I can't seem to make any sense out of the following vulnerability in OpenSSL: DH client certificates accepted without verification [Server] (CVE-2015-0205) ...
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2answers
108 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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Is it possible to perform one-way OTR MITM?

Here's something that is bugging me recently: suppose that me and my friend establish an OTR session and - as a result of that - DH key exchange is performed. My friend verifies my key, but I cannot ...
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1answer
80 views

Is it really worth to spend time on Telegram Crypto Contest? [closed]

Telegram is running this crypto contents. But what I heard from some people on the web is that they designed the contest in such a way that they made it practically impossible to crack. Is it really ...
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1answer
37 views

Is it feasible to create a new key for symmetric encryption for each message rather than negotiating a long lives session?

The normal method of providing an encrypted channel appears to be negotiating a session key (using Diffie Hellman or similar), then using this key for a long lived session. Even IPSec that is message ...
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630 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 ...
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24 views

Negotiate n-bits key with Diffie-Hellman protocol (or other key exchange protocol)

I've got ASCII message. I convert it to binary - then I've got 8*(ASCII message length) bits - let us assume this value will be called n. I have to negotiate key, which length (after conversion to ...
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2answers
127 views

A secure way to encrypt a connection between 2 clients securing against both passive and active adversaries

Recently I got interested in encryption and the methods behind them. So for a fun / school project I am building a program in python to encrypt data between two clients (chat and files). I'm just ...
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Why not use symmetric encryption?

Something very simple: most of us communicate most of the time with people we already know. Alice and Bob probably have physical contact, too. Yes, there are cases when whistle-blowers want to contact ...
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1answer
189 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 ...
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5answers
139 views

Using Diffie-Hellman to verify SSL Certificate?

I am fairly new to encryption and I need some help. I have a problem that I'm trying to solve. My problem is the following: I have a Web Server and an (iOS) App that that communicate with each ...
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1answer
815 views

In OpenVPN, is the dh1024.pem file dependent on the CA?

As the question already states, I'd like to know if the dh1024.pem file, generated by ./build-dh in openvpn, is dependent on the ca.(crt|key) file. The reason was that I needed to ./clear-all the ...
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1answer
268 views

which diffie-hellman group is needed for secure ike/ipsec

We're deploying ipsec on embedded devices and getting catastrophic performance from the diffie hellman 2048 group in ike.. afterwards the shared securet is used for 3des, sha1. ipsec negiation is ...
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1answer
100 views

How to best to secure data over HTTPS

My aim is to have an (iOS) app in which the user would login, then on sucsessful login, gain access to additional information over an encrypted webservice (undecided). From research, I understanding ...
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3answers
160 views

it is possible to decrypt HTTPS with the (private, public) pair if it uses DHE?

Assuming you have a PCAP file with HTTPS traffic and having the key pair (private & public), it is possible to decrypt the traffic if it uses Diffie Hellman Ephemeral? Using openSSL lib for ...
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6answers
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What is the simplest safe way to convey a password to another person? [duplicate]

What is the easiest way for two people – neither of whom are computer specialists and cannot meet in person – to send a password for an encrypted file that is attached to an email? The two simplest ...
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2answers
87 views

How to password protect a Truecrypt volume using a Diffie Hellman public key exchange?

I want to send a Truecrypt volume through email. Of course, I need to password protect it, and the recipient needs to know the password too. A Diffie-Hellman public key exchange would seem to be the ...
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3answers
181 views

Understanding Diffie-Hellman key exchange

I understand the diagram up till the point where Bob and Alice do a "Public transport" of their respective mixture. I am wondering how do Bob and Alice know what secret colour to add ( circled ...
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1answer
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How often should the DHE p and g factors be recycled?

I've been asked to enable DHE in our SMTP product. I'm stuck on this question: How often should the product regenerate its DHE p and g parameters? I've seen some implementations that use a cron job ...
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432 views

Does public key auth in SSH prevent most MITM attacks?

I found this article that claims asymmetric crypto signature of DH-obtained key prevents MITM: http://www.gremwell.com/ssh-mitm-public-key-authentication Key idea: The value of 'signature' is a ...
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72 views

Diffie Hellman Hash MITM

I've seen an application recently that used the Diffie Hellman algorithm. It is not a Ephemeral Diffie-Hellman implementation, but rather a Diffie Hellman one. After the secret keys have been ...
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1answer
273 views

Why OpenVPN is using both certificates and DH?

I am reading about OPENVPN and I am a little bit confused. In the OPENVPN howto website, there is a step by step setup guide for generating certificates and diffie-hellman (DH) params. However, I cant ...
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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 ...
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3answers
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How can DH provide a known secret to two parties over an unencrypted connection without it being intercepted via MITM?

Without using Private and Public keypairs, i do not understand how Diffie-Hellman is able to generate a secret key between two parties on the internet without passing something between that could be ...
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1answer
54 views

Is encrypting and subsequently sending a known clearext string after a Diffie-Hellman bad design?

I'm writing a small protocol that relies on a DH handshake, generation of a shared secret, and subsequent AES encryption/decryption using that generated secret. I want to add a built-in test message ...
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1answer
595 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 ...
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2answers
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Are Telegram secret chats secure assuming MTProto isn't?

For those who don't know: Telegram is a partially open source Whatsapp alternative (Server is closed source) which offers secret chats and normal chats. Secret chats are encrypted with Diffie-Hellman ...
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1answer
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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 ...
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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 ...
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728 views

Why don't more websites implement Perfect Forward Secrecy?

From what I understand, all it takes to enable PFS on a webserver is adding ephemeral cipher suites (ones that use DHE and ECDHE for the key exchange) to the list of cipher suites used in SSL/TLS ...
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465 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 ...
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What is the difference between Diffie Hellman generator 2 and 5?

Generating Diffie Hellman parameters in OpenSSL can be done as follows: $ openssl dhparam -out dh2048.pem 2048 Generating DH parameters, 2048 bit long safe prime, generator 2 This is going to take a ...
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What to do with the extra bytes in ECDHE-RSA-AES-GCM-SHA?

I'm trying to implement, as an exercise, a protocol based on the cipher suite ECDHE-RSA-AES256-GCM-SHA384. As I understand things, ECDHE is used for the key exchange, RSA for the authenticity of the ...
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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 ...
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328 views

Is it safe to use Diffie-Hellman public keys as nonces to protect against replay attacks?

I have an interesting case regarding protection against replay attacks. Under the assumption that Alice and Bob have used Diffie-Hellman key exchange to establish a secure temporary session, would it ...
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2answers
187 views

How secure is Samy Kamkar's Anti-MITMA Diffie-Hellman Key Exchange Technique?

I'm currently using Diffie-Hellman to encrypt data sent across an arbitrary link (can be ethernet, Wi-Fi, USB, bluetooth, etc), and I'm not a huge fan of the potential that DH is vulnerable to an ...
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3answers
267 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 ...
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2answers
394 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 ...
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96 views

How to generate DSA keypair for browserID

As a bit of a learning exercise, I'm trying to understand and implement a client for the Firefox Accounts Browser sync API. I'm up to the point where I'm trying to ask the server to give me a ...
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1answer
97 views

How much harm can an attacker do on the Diffie-Hellman exchange?

I'm looking at a system that uses an unprotected Diffie-Hellman exchange to negotiate a key for the session encryption. That Diffie-Hellman is not secure against man-in-the-middle attacks is textbook ...
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72 views

DHE Verification

I'm just struggling to get my head around this. In certificate signing with static Diffie Hellman the public key and certificate information is sent to the CA who verifies the certificate ...
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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 ...
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925 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 ...
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894 views

DH parameters recommended size?

I'm setting up EAP-TLS on my wireless router, and am currently generating DH parameters for FreeRADIUS. First, what do these parameters do? Also, what size should they be? I've been generating the ...
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1k 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 ...
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280 views

For DHE_RSA_.. Cipher Suites what is RSA used for?

In addition to achieving PFS with DHE, we want as little as possible to be revealed when the server's private key is revealed. So, what is RSA used for in DHE_RSA cipher suites? What does the server ...