for questions relating to key exchange protocols.

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4
votes
2answers
266 views

TLS server key: possible to sign another TLS server key?

If I have a valid (verifiable) certificate C_K_s that links the server key K_s to "www.example.com", is it possible to : use K_s to sign K_d, and let S_K_d be this signature use K_d as the TLS ...
4
votes
1answer
38 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 ...
4
votes
3answers
69 views

How many keys are used in this specific TLS 1.2 connection?

That shows the mechanism of the connection. How many keys are being used in this connection? What are they? Who knows them? What is the purpose of each key?
4
votes
2answers
118 views

How to establish a random OTR remote party as a specific individual?

In reading Glenn Greenwald's 2014 book No place to hide, one thing stood out to me as a bit odd. Greenwald details how Edward Snowden was insistent that Greenwald install PGP in order to communicate ...
3
votes
2answers
2k 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 ...
3
votes
7answers
344 views

How would I give an encryption key to only one person?

Let's say I have an encrypted message. I want to make it so that someone is able to decrypt it. The only way of giving it to them is online. For the purposes of this question, I can't call, mail or ...
3
votes
2answers
7k 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 ...
3
votes
3answers
323 views

Does the hash change the security of the Secure Remote Password protocol?

I'm implementing the Secure Remote Password protocol, and similar to this question, I'm wondering if I can use the SHA-512 hash function instead of SHA-1 currently being used. Would this help improve ...
3
votes
1answer
62 views

What is the best method for key exchange?

I have application working between server and client. All messages must be encrypted and decrypted. I use AES algorithm and I want method to hide the key. I found Diffie-Hellman algorithm, but my ...
3
votes
2answers
97 views

3rd party requires my server's public key for a secure connection?

I'm trying to integrate with a 3rd party service and they have requested our server's public key. I've sent it to them and they said they have configured it on their end. In order for me to make ...
3
votes
1answer
488 views

Why should an IKE responder change the cookie secret 'frequently'?

IKEv2 has the concept of a COOKIE mode, to attempt to prevent state exhaustion from floods of initiation requests from non-existent IP addresses: Two expected attacks against IKE are state and CPU ...
3
votes
2answers
43 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 ...
3
votes
1answer
208 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 ...
3
votes
2answers
86 views

Encryption in peer to peer chat

For a homework assignment I'm developing a chat service that will be able to communicate within a single network. The communication channel should be encrypted with RSA. Should I generate keypairs ...
3
votes
1answer
144 views

What public GPG key do I have to publish?

I just created a master key and two subkeys. The first subkey is used for encryption, the second one for signing. Now I am wondering what public key do I have to publish on my website. Does is ...
3
votes
1answer
47 views

Transferring of keys from key servers to recipients

When I download PGP keys from keyservers like so: gpg --search-keys steve@openssl.org How are the public keys transferred down to my machine? Is there a possibility of a MITM attack to serve me the ...
3
votes
4answers
802 views

Would a predefined shared secret key be good here

I'm a software developer working with hardware devices that are deployed on the field. Every now and then, I would need to update the hardware's firmware (upgrades, patches, etc) I'm thinking of now, ...
3
votes
1answer
128 views

Differing scrambling parameter generation methods in Secure Remote Protocol

RFC 2945 (The SRP Authentication and Key Exchange System) states, The parameter u is a 32-bit unsigned integer which takes its value from the first 32 bits of the SHA1 hash of B, MSB first. ...
3
votes
1answer
89 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 ...
3
votes
1answer
151 views

What is 0xXXXXXXXX.asc.sig and how can I generate this?

When I am exchanging PGP keys with someone, I receive the regular 0xXXXXXXXX.asc file and regularly receive a file called 0xXXXXXXXX.asc.sig. What is this file? How can I generate one and send it ...
3
votes
2answers
403 views

DEK, KEK and Master keying - simple explentation

This article is intended to be a simplified explanation sans drill-down for people wanting to understand the concept terms. What is DEK, KEK and MEK/Master key ?
3
votes
1answer
544 views

Encryption key exchange for Tor

I've been studying how Tor works - including the great QA "Why can a Tor exit node decrypt data, but not the entry node?". I understand the concept of onion routing and multiple layers of ...
3
votes
0answers
152 views

Main difference between Yahalom and Needham-Schroeder key exchange protocols

I am just wondering what is the main difference between the Yahalom and Needham-Schroeder key exchange protocols? Which protocol uses less computational power?
2
votes
2answers
2k views

Diffie-Hellman key-exchange: securing prime and base

As we know DH algorithm based upon 2 large prime numbers, which are used to be called as prime and base I am writing app which implements DH key exchange algorithm. From security point of view should ...
2
votes
2answers
647 views

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 ...
2
votes
3answers
200 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?
2
votes
1answer
361 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 ...
2
votes
1answer
206 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 ...
2
votes
3answers
561 views

Secure device pairing protocol

I need to implement secure pairing between two devices based on a short shared PIN code with no trusted third party. If you think about the way bluetooth devices pair you won't be far off -- my ...
2
votes
1answer
106 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. ...
2
votes
1answer
177 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 ...
2
votes
3answers
1k 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 ...
2
votes
2answers
273 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?
2
votes
2answers
117 views

Preventing a Computational DoS Attack in Public Key Cryptosystems

I'm designing a server which accepts anonymous messages using ECIES: as in, anonymous users send the server an ephemeral EC public key, and the server uses ECDH to derive a shared secret, and some KDF ...
2
votes
3answers
171 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?
2
votes
2answers
578 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 ...
2
votes
1answer
229 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 ...
2
votes
1answer
57 views

Https certificate change effects on established secure channels

I've a question regarding https certificate changes. Does anyone know any side-effects to changing the certificate, one signed with RSASHA1 to one signed with RSASHA256 for ex, while users already ...
2
votes
3answers
243 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. ...
2
votes
1answer
182 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 ...
2
votes
1answer
21 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 ...
1
vote
3answers
199 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 ...
1
vote
1answer
653 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 ...
1
vote
1answer
2k views

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 ...
1
vote
2answers
239 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 ...
1
vote
1answer
299 views

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 ...
1
vote
2answers
979 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, ...
1
vote
2answers
55 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 ...
1
vote
1answer
587 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? ...
1
vote
1answer
69 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 ...