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

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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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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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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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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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80 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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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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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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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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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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50 views

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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118 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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60 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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114 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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355 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 ...
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3answers
98 views

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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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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423 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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957 views

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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673 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 ...
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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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502 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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339 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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675 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 ...
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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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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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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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299 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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82 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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72 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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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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124 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 ...
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563 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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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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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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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 ...
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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 ...
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299 views

Using Diffie–Hellman key protocol to create a safe secret key

Let's say, I have a friend far from me and I want to send some secret messages to him. I have to say, I'm pretty newbie in security. That's why I'm wondering, does the Diffie–Hellman key exchange ...
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359 views

What are the implications of using the same DH parameters in a TLS server?

For a DHE cipher, nginx hard-codes the Diffie-Hellman parameters to use base 2 and a fixed 1024-bit prime (modulus) if no custom DH parameters are configured. These parameters are public (sent in ...
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1024-bit DHE vs 2048-bit RSA

Currently with apache/mod_ssl, if DHE is enabled then a 1024-bit ephemeral key will be used. I found the following quote in Adam Langley's blog: Ideally the DH group would match or exceed the RSA ...
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Is there a key length definition for DH or DHE?

I found this in wiki The Finite Field Diffie-Hellman algorithm has roughly the same key strength as RSA for the same key sizes. The work factor for breaking Diffie-Hellman is based on the discrete ...
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OpenVPN dhparam

One of the steps for setting up OpenVPN is running the command openssl dhparam -out dh1024.pem 1024. The man page tells me this 1024 value refers to the number of bits. Why is the value 1024 ...
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845 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 ...
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330 views

OpenSSL DH modp size

If OpenSSL is configured to use a DH for key exchange, e.g. TLS_DHE_RSA_WITH_AES_128_CBC_SHA, where does it take the size for modp (or even modp itself) from? The following is a screenshot from ...
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Diffie-Hellman and its TLS/SSL usage

I'm struggling to understand the (non-)use of Diffie-Hellman (DH) in TLS. DH has been around for a long time now, why does almost nobody use it, yet? DH is only being used for "key sharing", why ...
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Can manual hash verification defend against a DH MITM attack?

I understand how DH key exchange is vulnerable to a MITM attack. When Alice sends Bob g, p and her public key, if she also sent a value H that was a hashing of the values g,p, and public key all ...
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128 views

How to reduce the size of a key established with Diffie-Hellman?

When I generate a key with the a Diffie Hellman method (DH), the established shared key will be of the same size as the prime which is used. As far as I have read this should be at least 2000 bits for ...
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What's the hash for in ECDHE-RSA-AES-GCM-SHA?

Presumably the SHA is for deriving the AES key from the shared secret. Where else is the hash used? ECDH just does ECC (no hashing). RSA does masking and padding but this doesn't involve the ...
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Javascript Diffie-Hellman and AES protocols

I am using the BigInteger Javascript library to create a symmetric key using Diffie-Hellman protocol. I want to create 128,160 or 192-bit keys. After some research, I have found out that I should use ...