Questions tagged [diffie-hellman]
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 Diffie Hellman uses a “Safe” prime
I'm the developer for a web application that was recently pen tested. One of the vulnerabilities reported from the pen test is that our server uses an unsafe Diffie-Hellman prime in our key exchange. ...
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1answer
85 views
How does TLS work (RSA, Diffie-Hellman, PFS)?
I know "How TLS works" has been discussed numerous times here and crypto, but I am still somewhat confused and would like to summarize what I know so far 1 in this giant blob of text with the hope ...
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Usage of SSL_CTX_use_certificate
While building a context through openssl, if I do not provide a certificate by using the function SSL_CTX_use_certificate, would all the connections from that context default to anonymous diffie-...
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19 views
Can a DH param .pem file force the usage of only a single type of diffie-hellman exchange
Is it possible to create a diffie-hellman param .pem file to force the openssl ctx to use only a certain type of dh exchange. For example, I know that it can be used to set the length of the dh key, ...
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Understand DHE security in TLS
SSL Labs says that a website I control supports weak ciphersuites because they have DH 1024 bit, e.g. this one: TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x9f).
I tried to connect to the website from my ...
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1answer
40 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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2answers
159 views
How to optimize the diffie hellman key exchange algorithm
I am making a chat feature in my app where I want to encrypt it E2EE, but the problem is when I start to calculate the public key (public key = g^private % n) it takes a decade to get it done. I need ...
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1answer
106 views
BouncyCastle and Microsoft Cng ECDH secret key mismatch
I'm trying to refactor some client-side code from BouncyCastle to Microsoft Cng. I've figured out how to convert key format(ECC key blobs) between them, but I couldn't calculate the same secret.
...
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74 views
Why Diffie-Hellman instead of just share the secret [duplicate]
I read that D-H is used to make a shared secret between parties that then they use to encrypt the messages.
This is used in TLS, for example, after the server has authenticated itself with a ...
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1answer
99 views
Signal Protocol: How is identity exchanged if a key exchange hasn't happened yet?
On Signal's blog they mention that keys for accessing your profile are exchanged normally with your contacts using the Signal Protocol just like messages are (implying they are already contacts and ...
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0answers
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WPA technical doubts (3)
This is the third post about the set of doubts that came up when I tried to understand WPA3. I am new to this world of cyber-security so every bit of help is welcome!
Someone told me that in WPA2 ...
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1answer
57 views
Different Diffie–Hellman key per site?
I recently put each of my sites through the ssl labs analyzer and now have them all running with an A+ getting perfect scores with every metric except Key Exchange at 90.
As part of this I have ...
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53 views
Advantage Of ECDH-RSA over RSA Ciphersuites In TLS
If ECDH-RSA is used for key exchange, this is what happens:
The server has its public ECDH parameter embedded within its certificate. The client generates its public ECDH parameter, extracts the ...
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2answers
155 views
Diffie-Hellman protocol CA, confusing
In the Diffie-Hellman protocol, if the participants have their own private key and a generated public key. How can we determine whether or not they have a trusted CA for authentication or just the ...
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1answer
164 views
understanding MITM attack [duplicate]
hi Everyone please correct me if im wrong for my understanding for the man in the middle attack used in a variant of diffie hellman key exchange .
am i right to say that a protocol is susceptible to ...
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1answer
108 views
Why use a separate key exchange method like DH during the TLS handshake [duplicate]
Ok first off I'm very familiar with the TLS handshake, the purpose of PKI and key exchange methods.
My question is why use a complicated key exchange method like Diffie Hellman when the client could ...
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2answers
529 views
Is server public key and Diffie Hellman public are the same?
I am trying to understand the working of TLS. I understand that there are various way to generate the master secret used to encrypting the data. Such as DH (Ephemeral DHE) and RSA. I understand that, ...
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1answer
615 views
diffie-hellman size 2048 and key with size 1024
I want to increase the security of my Tomcat and to configure diffie-hellman module size 2048.
I want to add to my CATALINA_OPTS -Djdk.tls.ephemeralDHKeySize=2048
What happens if I have configured it ...
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80 views
Diffie-Hellman in Android File Transfer application [closed]
I'm working on the famous android app to transfer files using WiFi-Direct technology:
https://github.com/Miserlou/Android-SDK-Samples/tree/master/WiFiDirectDemo
I want to implement a key exchange ...
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1answer
1k views
How can disabling Diffie-Hellman cipher for packet inspection be secure?
I have noticed that a number of network packet monitoring tools on the market today seem to have roughly the same recommended configuration parameters as described below:
Disable Diffie Hellman in ...
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1answer
77 views
Exchange of public keys with DHE-RSA
The paper "Imperfect Forward Secrecy: How Diffie-Hellman Fails in Practice" by Adrian et al claims that the NSA might be able to eavesdrop on a large percentage of TLS connections, because they ...
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How to perform a MITM attack on SSH exploiting the Diffie Hellman key exchange
I have an open-ended project for a class and I picked to make a tool/use existing tools and applications to exploit the Diffie-Hellman key exchange to be able to inject, modify and delete messages ...
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1answer
2k views
Is Diffie–Hellman key exchange protocol vulnerable to man in the middle attack?
Diffie–Hellman key exchange protocol vulnerable to man in the middle attack? If yes, then what type of MITM is that? I believe that is a replay attack or a relay attack, not sure though.
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Setup Wireshark to decrypt TLS_DHE
I have a passively sniffed traffic dump of client/server were packets are encrypted with cipher suite
Cipher Suite: TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 (0x009e)
With a Logjam attack I managed to ...
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1answer
95 views
Does LoraWan protocol's Over The Air Activation run Diffie Hellman?
I am looking at the LoraWan protocol specification and I want to capture the over the air activation of a device. So far I have seen the:
https://zakelijkforum.kpn.com/lora-forum-16/over-the-air-...
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2answers
290 views
OpenSSL Base64 output has wrong length
I try to generate an ECDH P-256 key pair as required for web push messages.
openssl ecparam -name prime256v1 -genkey -noout -out priv_key.pem
... generates the keys.
openssl ec -noout -text -in ...
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1answer
545 views
Why does TLS 1.3 deprecate custom DHE groups?
According to the second draft of the TLS 1.3 specification, custom DH groups have been deprecated. As we all know, hardcoded DH groups are vulnerable to a precomputation attack that allows retroactive ...
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1answer
138 views
RSA relation to SSH key exchange
I do not fully understand SSH. I was hoping someone could fix my confusion.
When you generate an ssh key pair, you create four files.
authorized_keys, id_rsa, id_rsa.pub and known_hosts
My ...
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1answer
273 views
Limitations of TLS Inspection when using Diffie-Hellman
It is my understanding that TLS Inspection can be carried out of two different ways:
1st Approach: Using a proxy server which negotiates TLS with both ends.
In this scenario, there would be 2 ...
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1answer
47 views
Visual verification of DH parameter hashes vs derived password hashes
Let us assume the following: Alice and Bob are performing Diffie-Hellman key exchange over an unprotected channel. Eve is an active attacker (capable of dropping, modifying and constructing packets on ...
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1answer
168 views
How can one guarantee that a Diffie-Hellman initial key exchange is not stored? [duplicate]
I might have missed parts of the technicality when it comes to the initial state of the key exchange. However, If I'm not wrong, if the initial key exchange is done over an insecure channel, how can ...
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1answer
110 views
Diffie Hellman master secret TLS1.2
I have been trying to calculate the master secret used to encrypt some data using the client public key B, the server private key a and the client and server random values. I have calculated k=B^a, ...
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1answer
328 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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0answers
237 views
Diffie Hellman Pre Master Secret too long
As far as I understood, when using Diffie Hellman, the pre master secret is generated as follows:
Alice and Bob agree on a generator g and a prime p
Alice chooses a primary key a, calculates A = g^a ...
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1answer
323 views
What's the usage of the signature algorithm in TLS_DH_* cipher suites?
According to RFC5246 A.5 there are cipher suites TLS_DH_RSA_* and TLS_DH_DSS_*.
How / where does the signature algorithm RSA resp. DSA from the cipher suite come into play when using (non-ephermal) ...
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1answer
431 views
Possible MITM attacks on ECDH-RSA or ECDHE-RSA prevents
As I understood a simplified ECDH-RSA key exchange protocol works like below
Alice request Bob for its ECDH public key
Bob generates ECDH parameters and sign them with a CA provided RSA certificate. ...
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1answer
271 views
TLS - DHE_DSS: How does client know public DSS-server key?
I wonder where the public server key g^x for DSS authentication is communicated to the client when a DHE_DSS cipher suite is used in TLS 1.2. Precisely:
A DSS certificate contains crypto parameters (...
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2answers
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Diffie Hellman Group Matching to IPSec Encryption Algorithm
I'm looking for help determining acceptable Diffie Hellman (DH) Groups for specific IPSec IKE and ESP Encryption Algorithms. The goal is to choose DH groups that provide adequate protection for the ...
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1answer
275 views
Online Diffe-Hellman Tool
So I stumbled upon this website which provides a service to generate Diffe-Hellman paramaters online for free to the public.
Surely using a website like this would be a bad idea to use in a ...
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1answer
220 views
Why send HMAC in reverse direction when performing verified DH with downgrade protection?
The purpose of this procedure is that Alice and Bob perform a verified Diffie-Hellman key exchange. It goes like this:
Alice sends her supported signature schemes to Bob. It just says "supported ...
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1answer
662 views
Will changing the TLS Diffie-Hellman key exchange bit length from 1024 to 2048 cause client/browser compatibility issues?
Recently discovered the need to upgrade our DH key exchange length (used for TLS) from 1024 bits to 2048 bits (due to Logjam exploit and other factors). The question is: How will making that change ...
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1answer
113 views
What's the point of the second SA exchange in the Create_Child_SA exchange in IPsec
I have problems understanding why you would negotiate crypto-algorithms in the Create_Child_SA request in a IKEv2.
During IKE_SA_INIT you negotiate cryptographic algorithms which I assume (correct me ...
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1answer
1k views
How likely is that my ECDHE-RSA-AES256-GCM-SHA384 application will be cracked? [closed]
I am using the following chain in my cipher: ECDHE-RSA-AES256-GCM-SHA384
I am wondering if there's a weak chain in this cipher that might allow my application's communications to be cracked?
I'm new ...
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2answers
4k views
Why is the reuse of the Elliptic curve Diffie–Hellman (ECDH) public server param considered bad?
When reviewing the SSL/TLS configuration using Qualys SSL Labs, I've found that the reuse of the Elliptic curve Diffie–Hellman (ECDH) public server param was flagged.
Why is the reuse of the Elliptic ...
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1answer
532 views
Key exchange during IKE_AUTH phase of IKEv2
This is what a casual IKEv2 handshake looks like :
Initiator Responder
| ...
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1answer
459 views
What is the meaning of KEX DH host key and KEX DH H signature in SSH key exchange
During the Diffie-Hellman key exchange, the server sends a Diffie-Hellman Key Exchange Reply (31) message back to the client. This message contains the DH server f but also two other pieces of ...
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1answer
97 views
Logjam definition question
As I understand it, the Logjam TLS attack is an attack that downgrades the DHE cipher suite used by the server to DHE_EXPORT. Where the client thinks it is talking DHE 512 and the server things it's ...
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1answer
33 views
Secure application data
I have a private client/server application that trying to secure the data transmitted through public network. The encryption/decryption method is private too. Client and server uses DH key exchange ...
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1answer
4k views
When exactly is Diffie-Hellman used in TLS?
I'm aware that Diffie-Hellman is a key exchange algorithm whereas RSA is an asymmetric encryption algorithm.
I have the following questions:
During TLS handshake, will both RSA and DH be used?
(I ...
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221 views
Is ECDH easier than DH to be broken?
As I am a security newbie, this post might have lots of misconceptions about security. If so, please let me know
I've heard that ECDH is preferable to DH because its smaller key size and lower ...
