Key exchange protocols

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Is End to End security possible without physical contact?

I noticed that a lot of messaging start to provide "End2End" security, but I wonder how this can be possible without a key exchange between the the two clients. To my understanding to provide real ...
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1answer
23 views

Best practices for encryption from web<-> specific client

If we want to allow sensitive data between a web server and specific client only, is there anything more that can be done besides the following? Note that this is potentially a duplicate of ...
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6 views

Key Confirmation Attack [Key Distribution Center (KDC)] [migrated]

Okay this is how I understood it according to this: Alice A establishes a connection to KDC and prepares for session key Exchange R1 A encrypts the request with her key kA(A, B) meaning "need a ...
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1answer
33 views

User Key pairs and Man-in-the-middle issues

I'm trying to wrap my head around how to exchange user's keys with a server. Maybe during sign-up a JS applet generates a key-pair for the user. These keys would be used for signing subsequent ...
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1answer
30 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 ...
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1answer
30 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 ...
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27 views

Distribution of key by server

I have read that in asymmetric cryptography, a system admin can generate key pairs on the server. After that, the users will be given the generated key pairs and this is an efficient way of doing this ...
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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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2answers
100 views

How do certificates stop this man in the middle attack?

Alice and Bob are trying to set up a secure conversation, but unknown to them in the middle is Eve, who can intercept and modify all packets sent between them. The communication goes as follows: ...
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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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1answer
60 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 ...
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0answers
36 views

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
77 views

How to incorporate the man-in-the-middle

I am designing a web-based back-end for an online service. The service could support web based portals and mobile apps as front end. But I am stuck on how to support third-party, i.e untrusted, web ...
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1answer
97 views

Are VPNS vulnerable to active man in the middle attacks?

I know that with SSL/TLS, man in the middle attacks are not possible. For example if Alice and Bob are trying to communicate and Trudy is trying to perform a man in the middle attack, then when Alice ...
8
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1answer
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
96 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. ...
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0answers
70 views

ElGamal for ECC - Not working with Edwards curves (ed25519)

I know the usual way of using encryption/decryption with ECC is DH, however, this only works with two keypairs of exactly the same kind, for example two curve25519- or two p256-keypairs. With ...
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1answer
50 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 ...
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1answer
75 views

Why do we encrypt ephemeral Public key in Encrypted Key Exchange

Encrypted Key Exchange can resist off-line dictionary attack Protocol : A ---> B : Ep (PK) B ---> A : Ep(Epk(K)) K is Session Key generated by B PK is an ephemeral public key ...
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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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1answer
80 views

How could SSL certificate affect the symmetric key length?

This article in GoDaddy support knowledge base says All of our SSL certificates support high-grade 256-bit encryption How would they not support it? The SSL certificate contains keys for ...
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1answer
131 views

Key Exchange using RSA

I'm trying to do key exchange using the following scheme. Server generates an RSA-2048 key pair and sends the public part to the client Client generates an RSA-592 key pair (I have to use RSA-592 ...
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59 views

Verifying the owner of a signing key

I'm using elliptic curve cryptography (curve25519 and ed25519) for key exchange and signing. The signing and key exchange keypairs are independent. I need two users to be able to verify each other's ...
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1answer
300 views

rolling code & keyless entry system [closed]

The security industry typically uses rolling code algorithms to authenticate sender & receivers in keyless entry systems, which is called RKE (ex: KeeLoq). In key-less smart key car system, The ...
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1k 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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2answers
86 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 ...
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1answer
105 views

How can I generate some public and private keys on both sides with low overhead?

We have an Authority Center (CA) generating some public and private keys for each client (more than one pair for each client). One method for sending keys to client is sharing a secret key between CA ...
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1answer
64 views

MITM protection, key distribution

I want to make sure each of my apps users only get their own data, and that nobody tampers with it or sniffs it in a MITM fashion. Encryption of everything should be the solution, right? But how do I ...
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2answers
149 views

What are the alternatives to ECDSA for an authentication protocol?

In an authentication protocol, S has a public/private key pair known to C, and S and C have established a secure channel (for example, using DH or ECDH, or any other key exchange protocol). C wishes ...
3
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1answer
41 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 ...
2
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1answer
79 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 ...
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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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107 views

In IKE protocol; what is the PRF? [duplicate]

In IKE protocol; what is the PRF ? What is "the generation of a key based on modeled random oracle hash functions"?
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162 views

SSH using pre-existing session (symmetric) keys

Is there at present a way to open a SSH connection using pre-existing symmetric session keys? In other words, if I create a list of symmetric keys can I send that list to the recipient on a CD or USB ...
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2answers
101 views

Is it safe to use a ECDSA public key as a password seed for GCM/AES?

Two peers already exchanged their ECDSA (curve secp256k1) public keys using a secure channel. They want to establish an authenticated encrypted channel between them. They will use CCM mode and with ...
5
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1answer
1k 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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1answer
60 views

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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1answer
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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9answers
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Are there any systems out there that use a one-time pad?

I'm still new to information security, but I have read a bit about the one-time pad. The point that sticks out to me the most is that it is supposedly unbreakable. Has this method of encryption ever ...
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2answers
500 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, ...
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2answers
537 views

GSM A5/1 encryption: Key management

I'm currently studying the A5/1 algorithm used for GSM encryption. I understood how thanks to the symmetric private Key and a public counter frame one can encrypt the communication between A and B. ...
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3answers
111 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?
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1k 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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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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Does Diffie-Hellmann (DH) key exchange protocol lower Off-The-Record protocol (OTR) security level?

Off-the-Record protocol employes Diffie-Hellman key exchange protocol (DH). DH protocol does not provide authentication of the communicating parties and, according to many sources, is vulnerable to ...
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139 views

Key-Exchange Algorithms VS Local Key Generation?

I was wondering the difference in term of Security, Computational cost and Network overhead between the use of : A Key-Exchange Algorithm (e.g. Diffie–Hellman) to set up a symmetric key. The ...
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1answer
699 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 ...
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1answer
145 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 ...