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

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How to verify the signature of DHE_RSA server parameters (TLS 1.2)?

By reading the TLS 1.2 specs I have been able to manually decrypt/encrypt pretty much all the steps of a TLS connection (DHE_RSA_AES_CBC_128_SHA cipher suite). One of things I am missing is how to ...
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Why is random DH group recommended over a standard group?

I know in light of logjam there have been recommendations to generate your own DH group (https://weakdh.org/sysadmin.html). It seems to me that leaving this task up to the end user is much more likely ...
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39 views

Difference between Hybrid encryption and Diffie-Hellman key agreement?

Can someone explain me the difference between the Diffie-Hellman key agreement (DH encryption) and Hybrid encryption? As to my knowledge DH key agreement uses public and private keys to generate a ...
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If we should not reuse primes in DH, shouldn't we not reuse ECDH elliptic curve properties? [migrated]

An article How is NSA breaking so much crypto? describes NSA's methods for breaking encryption. If a client and server are speaking Diffie-Hellman, they first need to agree on a large prime number ...
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16 views

DTLS and Ephemeral Diffie-Hellman [duplicate]

In the DTLS handshake, the two parties involved in the communication must authenticate each other by means of certificates, and after that they perform an ephemeral Diffie-Hellman key exchange, with ...
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which algorithm/hash can possibly encrypt and decrypt certain data regardless of size?

I have intercepted some data for which i don't know which algorithm has been used to encrypt this data, this data has been for sure encrypted before transmitting, to decrypt the data i should ...
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416 views

Is the OpenSSH server using a fallback, hard-coded DH parameter for 2048bits?

I'm toying around with OpenSSH configs and poking at the Diffie-Hellman parameters. I'm using GDSSecurity's tool to check DH settings and this page to view other SSH settings. For funsies, I removed ...
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62 views

Is OpenSSL generating Diffie-Hellman parameters that are safe for use in TLS or SSH servers?

I would like to generate Diffie-Hellman parameters on a Debian GNU/Linux "Jessie" 8 with OpenSSL. Lets assume the system CSPRNG was seeded with some real random data. On such a system, is the result ...
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32 views

Diffie Hellman prime attributes

If I generate a Diffie-Hellman prime openssl dhparam 512 -text (deliberately of small size to keep the paste size below small; I know minimum is 2048 and up), what are the different parts of the ...
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67 views

Q: What happened to socat?

I saw elsewhere some discussions on an error (or backdoor) in socat but find it difficult to get from the (anyway not well ordered and fairly large volume) materials the essence of what had actually ...
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71 views

How can a RSA-2048 certificate be vulnerable to logjam attack? [duplicate]

Most likely I am missing some fundamentals: Our web servers are secured with TLS encryption. We use RSA-2048 bit certificates. The logjam attack targets the DH algorithm. How can our web servers be ...
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What is the current security status of Diffie-Hellman key exchange?

There is a web site weakdh.org, whose name alone would certainly cause some feeling of uncertainty in using DH among people who are not experts IMHO. Could some knowledgeable person kindly say ...
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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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3answers
1k views

Is 8192 Diffie-Hellman overkill?

I've finally ran SSL server test on my server and was presented with: This server supports weak Diffie-Hellman (DH) key exchange parameters. Grade capped to B. So I tried to generate stronger ...
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1answer
68 views

How to encrypt something with a key? [closed]

I read a lot about security on the internet, especially how services like telegram work with their encryption and how they do it. I also heard of the Diffie-Hellman Key Exchange, which was quite ...
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1answer
37 views

Filtering safe primes for Diffie Hellman on OpenVPN

When creating Diffie Hellman parameters for OpenSSH, there's a two-step process which looks like this to generate and filter secure primes for Diffie Hellman key exchange: ssh-keygen -b 4096 -G ...
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2answers
151 views

In Ephemeral Diffie Hellman Key Exchange - what is actually ephemeral?

Just starting to learn about Diffie-Hellman, and it seems simple enough, but I am struggling to find any resources that explain in an Ephemeral Diffie Hellman Key Exchange, what it is that is actually ...
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4answers
5k views

Why is key exchange necessary at all?

Let's say "Alice" and "Bob" want to communicate with each other over an insecure network. Using Diffie–Hellman key exchange, they can get the same symmetric key at last. However, as I understand, ...
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260 views

Using a stolen certificate on a server

Yesterday I asked the following question regarding what would happen if you placed a stolen certificate on your own server and edited the 'host' file so that the DNS name matched: Could a stolen ...
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What DH Group size do TLS Ephemeral DHE ciphers use?

In SSL/TLS, the Client and the Server have the option to use an Ephemeral Diffie-Hellman exchange to establish a shared secret for which to seed the ensuing Master Secret and Session keys. In the ...
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1answer
84 views

What's the algorithm to generate a modulus and a base for a Diffie-Hellman key exchange app?

I have a school project in which I have to write a java console application that can be used for key exchange between two people. All is fine and well, but finding good base and modulus seems to be a ...
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223 views

Diffie-Hellman large prime number weakness. Is this concept valid? If so, how can this be remediated by end-users/admins?

So I saw this blog post on “How is NSA breaking so much crypto?”. The basic idea of this blog post is this: There is an inherent weakness in Diffie-Hellman that stems from services using the same ...
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Does changing /etc/ssh/moduli impact previously generated keys?

My company does a lot of automated file transfers over SSH/sftp with banks, etc. A recent SSH upgrade on a server dropped support for the old/weak diffie-helman-group1-sha1 key exchange protocol in ...
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2answers
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Does SSL doesn't work without a secondary Symmetric/Asymmetric session key?

I keep reading that Symmetric session key is used in SSL after handshake only for faster performance but isn't true a secondary session key either Symmetric or Asymmetric key generated by the client ...
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What algorithm should I use to avoid the error “ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY”?

I got a CA cert by submitting my CSR from GoDaddy, after applying a certificate to my Tomcat web server. When I access my website using Chrome or Mozilla I face the error: ...
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129 views

How to Build Pre-Master Secret [duplicate]

I'm implementing a TLS-like system, which uses ECDHE-RSA-AE-GCM-SHA, and I've faced two interrogations. At the end of the handshake ( and before the ChangeCipherSpec message), both the client and the ...
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68 views

RSA signature on TLS

In a TLS handshake using ECDHE-RSA, the ServerKeyExchange frame must include the ECDHE ServerPublicKey, signed with its RSA private key, as specified in the RFC 4492. Got it. Trying to implement an ...
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124 views

Specificity of ECDHE in a TLS handshake

It's just a short question, but I haven't find a clear answer yet... It's in the frame of a TLS-ECDHE handshake. Where does the specificity of the ECDHE, over the DHE, appears ? At which point do ...
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407 views

Usage of Ephemeral Diffie-Hellman ciphers in 2015 and beyond

In determining TLS standards for my company, I have come to wonder why all recommendations still suggest the use of the Ephemeral Diffie-Hellman TLS ciphers starting in TLS_DHE_xxx Background and ...
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367 views

Diffie-Hellman and MIM attack, and server identity

Diffie-Hellman and MIM attack: When variants of Diffie-Hellman algorithms like DHE, ECDHE etc. are used in SSL handshake for key exchange then can it become prone to man in middle (MIM) attack. ...
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541 views

Is ECDH for SEC P-384 and P-521 broken in Windows 10 / Windows Server 2016 TP3?

UPDATE: Proof of concept code here, console output shown below and all involved certificates are here. Just noticed that ECDiffieHellmanCng.DeriveKeyMaterial(...) behaves differently on Windows 8.1 ...
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Where in a TLS connection can I get the signature of the content sent by the server?

I want to be able to prove that a given content returned by a HTTPS server was in fact served. I have looked over the whole TLS protocol and I found I can use ServerKeyExchange to get the server's ...
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Diffie Hellman parameters still calculating after 24 hours

I have a fresh install of Arch Linux on a RaspberryPi model B. I'm setting up OpenVPN and using easy-rsa with OpenSSL 1.0.2d to generate initial keys and certificates. All went fine until I ran ...
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1answer
402 views

Diffie Hellman parameters still calculating after 24 hours [duplicate]

I have a fresh install of Arch Linux on a RaspberryPi model B. I'm setting up OpenVPN and using easy-rsa to generate initial keys and certificates. All went fine until I ran ./build-dh. It is now 24 ...
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72 views

How to inform other sysadmins their email encryption is broken [closed]

Does anyone have a good template email to use to send to remote system/mail/security administrators to alert them to the fact that emails to them would not be getting through either at all or securely ...
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280 views

ECDH BouncyCastle KeyAgreement length

I am attempting to obtain a shared secret using BouncyCastle's ECDH methods in C#, however I am receiving a shared key which is much shorter than the 48 bytes I expect it to be. I have a trusted ...
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5answers
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Why can't I MitM a Diffie-Hellman key exchange?

After reading the selected answer of "Diffie-Hellman Key Exchange" in plain English 5 times I can't, for the life of me, understand how it protects me from a MitM attack. Given the ...
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How to verify the usage of dhaparameters configuration from command-line?

Although Qualys will happily do it for Internet-reachable systems, some of ours are on private networks. I'd like to be able to verify them all remotely. Is there a "quick" recipe -- something based ...
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550 views

Cipher suites vulnerable to logjam

The following is a list of ciphers, how to know which ciphers are vulnerable to LogJam attack? Client shared list of ciphers: TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA ...
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82 views

What are 'screened' DH groups?

Currently it's recommended to do something about the contents of /etc/ssh/moduli. I've seen two ways: to strip all moduli of less than 2047 bytes size from the file. to recreate them using ...
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78 views

Must a Diffie-Hellman group value persist?

I've been reading about the Logjam attack on Diffie-Hellman and about how to secure our TLC-based web servers based on the recent findings. The guide suggests that we create a Unique Diffie-Hellman ...
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1answer
781 views

How ECDHE is signed by RSA in ECDHE_RSA cipher

About ciphers that use ECDHE as Key Exchange and RSA as Authentication: How exactly this two algorithms work together, is ECDHE process encrypted by RSA public key? What are the DH parameters? ...
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What is the role of RSA in ECDHE-RSA? [duplicate]

I have read some textbooks and not found a convincing explanation. In the cipher suite ECDHE-RSA-AES128-GCM-SHA256, what is the role of RSA in the first part (ECDHE-RSA)? This part of the cipher ...
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1answer
141 views

Do Diffie-Hellman parameters need to be recreated regularly?

Having generated 2048-bit DH params, do I need to regenerate them regularly? If so, how frequently should I do this?
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How to check if a server is not vulnerable to Logjam?

In response to Logjam I want to prove I've hardened my services. I know that the DH param has to be 2048 bits at least and self generated. But I am unable to find a way to actually check this for ...
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How 'Logjam' attack affects openID since it uses Diffie-Hellman key exchange method?

According to the Diffie-Hellman key exchange get affected by logjam, and openID uses this to establish an association. So how this going to affect OpenID?
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What is Logjam and how do I prevent it?

I heard there is a "new" TLS vulnerability named Logjam, what does it do and how do I prevent it?
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108 views

Should diffie-hellman parameters be unique to a vhost

So I'm setting up one host to serve multiple SSL sites. I've been following various guides like https://cipherli.st/ and https://wiki.mozilla.org/Security/Server_Side_TLS and they both suggest to ...
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Unable to establish handshake using DH key exchange [closed]

I have a requirement to use the cipher suite: DHE-RSA-AES256-GCM-SHA384 I configured to use the required cipher suite on both server and client. During tests, I noticed that the handshake is failing ...
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261 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 ...