Key exchange protocols

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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 ...
3
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1answer
576 views

ECDH and Forward Secrecy

I just read about ECDH and while getting a overview over the process, I noticed that this key exchange method does neither provide any forward secrecy, nor does it protect against replay-attacks, ...
2
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1answer
111 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 ...
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3answers
164 views

Cryptography key gathering tool

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 ...
3
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1answer
188 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 ...
-1
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1answer
640 views

GPG advantages / disadvantages, is it useful or secure? [closed]

I thinking about GPG, is very widely used, but is secure? Why and where we using GPG? I found an article from 2002, but is very old.
2
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2answers
407 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 ...
4
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1answer
149 views

Share or not share public key for servers?

In order to encrypt communications from our (custom) client to our (custom) servers our current scheme is a bit like this: Client uses the bundled public key A to encrypt some random key material. ...
1
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1answer
192 views

Secure Encrypted Chat Protocol [duplicate]

Possible Duplicate: Is there a way to negotiate a secret between 2 parties with no prior knowledge? Imagine two clients who want to establish a secure connection over a server. Both clients ...
2
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3answers
183 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?
4
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1answer
625 views

Are SSH packets encrypted even before new keys are sent?

What format does SSH use to exchange (encrypted / plain) packets before new keys are derived? SSH Document says that after key exchange, client and server use negotiated algorithm to encrypt the ...
0
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3answers
922 views

Are there flaws in this simple key exchange?

I'm reviewing for a computer security exam. Here is a simple scenario: Suppose that someone suggests the following way to confirm that the two of you are both in possession of the same secret key. ...
0
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2answers
742 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 ...
7
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1answer
741 views

How do i store Diffie-Hellman parameters in a X.509?

In there paper Authentication and authenticated key exchange Diffie, van Oorschot and Wiener recommend to insert the DH parameters into the certificate of Alice. As a result an attacker can not change ...
4
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2answers
248 views

What steps can you take to make offline cracking of SRP harder?

In the aftermath of the Blizzard hack, what steps can I take to make offline cracking of SRP more difficult? My question assumes that your database is already gone and that you implemented SRP more ...
6
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1answer
9k views

How to implement an API-Key-Mechanism

first of all: I am quite unsure about the questions title, so if you have a better idea, please feel free to tell (: I would like to know about best-practise examples where services (like Twitter or ...
2
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3answers
624 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
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1answer
165 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
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3answers
292 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 ...
5
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2answers
272 views

Authenticating client without hardcoding key?

A basic question, but I'm not a master and this is puzzling me- How is it possible to authenticate a client from the server's perspective? i.e. imagine you're the server, and you want to give the ...
4
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2answers
207 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
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3answers
886 views

In the Diffie-Hellman key exchange, how is the shared base key 'p' known and how are A and B, protected from Eve?

I'm trying to wrap my head around Hellman, Diffie, and Merkle's key exchange design, but after reading the Wiki article about it, I can't figure out how the commonly known factor ('p', I think) comes ...
4
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3answers
887 views

Diffie Hellman - how large should the random number be?

When using the Diffie Hellman exchange with the second Oakley group 1024 bit Prime per RFC 2409 (*), how large should the random numbers generated by both sides be? In RFC 2631 this is called the ...
3
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3answers
243 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 ...
18
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1answer
12k views

What key exchange mechanism should be used in TLS?

There are many key exchange mechanisms that can be used in TLS. Among them are RSA, ECDH_ECDSA, ECDHE_ECDSA, ECDH_RSA, ECDHE_RSA and others. Which of these are more cryptographically secure and can be ...
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2answers
506 views

Is it possible to have a key for encryption, that cannot be used for decryption?

For example, a server might have some encrypted logs or storage or whatnot, that would only be used for reference later. This way even if the server is hacked, everything is still OK until the hacker ...
7
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1answer
3k views

Ways to sign gpg public key so it is trusted?

I have a service through SSL which gives the user a code for a specific reason. I want to sign the code with the web server's private key (gpg --clearsign) and send the signed code along so that they ...
194
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13answers
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How is it possible that people observing an HTTPS connection being established wouldn't know how to decrypt it?

I've often heard it said that if you're logging in to a website - a bank, GMail, whatever - via HTTPS, that the information you transmit is safe from snooping by 3rd parties. I've always been a little ...
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3answers
343 views

DHE exchange and client authentication

If a server has a known public key and a Diffie-Helman exchange is performed and signed by that key, is there any benefit to authenticating the client before establishing a secure channel instead of ...
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2answers
4k views

Is 1024bit Diffie Hellman key exchange secure?

My system uses AES-256, 4096bit RSA CA key and 2048bit RSA keys for servers together with SHA-256 signing. Does using 1024bit DH key exchange lower its security? I read on one mailing list that ...
11
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2answers
2k views

Which cipher suites with AES cipher provide forward secrecy?

Does standard AES with RSA (reported by Opera as TLS v1.0 256 bit AES (1024 bit RSA/SHA)) provide perfect forward secrecy? Which SSL3.0 and TLS1.0 ciphers do provide forward secrecy? Which ciphers ...
10
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1answer
4k views

Where do I get prime numbers for Diffie-Hellman? Can I use them twice?

I realise it's very hard to generate suitable prime numbers and generators for the Diffie-Hellman key exchange. What is the best way to generate them? And if I have one, can I use it twice? ...
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3answers
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Is this prime number large enough / too large for a Diffie-Hellman for AES-256?

I'm using a Diffie-Hellman key exchange to encrypt data using AES-256. The prime number I'm using is the one from the 8192bit group specified in RFC 3526 (page 6). Page 7 suggests that, with a 620 ...
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1answer
165 views

Theorical question on encryption methods [duplicate]

Possible Duplicate: Encryption strategies for multi users access in production systems I would like to develop a service on wich clients would connect and retrieve informations. These ...
8
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3answers
516 views

Which authentication at the end of the Secure Remote Password protocol?

For the the client and server to prove to each other that they have the same premaster shared key, the original author suggests this: M = H(A | B | K) --> <-- H(A | M | K) ...
9
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1answer
329 views

Optimal variable sizes in the Secure Remote Password protocol

I am implementing the Secure Remote Password protocol: U = <username> --> <-- s = <salt from passwd file> a = random() A = g^a ...
6
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2answers
569 views

Implementing Secure Remote Password: Constructing the verifier

The SRP protocol as described in RFC 2945 generates the password verifier: x = SHA(<salt> | SHA(<username> | ":" | <raw password>))` v = g^x % N I have three questions: why use ...
3
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1answer
90 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. ...
6
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3answers
942 views

Using Secure Remote Password without sending the username in the clear

To initiate a key exchange using the SRP protocol the client sends the username so the server can look up the salt and password verifier. Is there a simple way to change this so that an evesdropper ...
5
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1answer
237 views

Using Secure Remote Password without embedding the modulus

The SRP protocol as described by the author assumes that the large safe prime modulus and generator are embedded into the client and server rather than being transmitted as part of the protocol. ...
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2k views

How to exchange RSA public keys safely between two parties?

How to exchange RSA public keys safely between two parties via internet?
8
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1answer
227 views

distributing files to VPN partners

suppose i've created VPN certificates for a certain VPN-RoadWarrior-Client, expressed in the files VPN-RoadWarrior-Client.key and VPN-RoadWarrior-Client.crt*, however VPN-RoadWarrior-Client is ...
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2answers
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Diffie Hellman c# implementation

Hallo all, For a test project I have tried to implement the (famous) Diffie Hellman algorithm for safe key exchange. Now I have written this in C#: using System; using System.Collections; using ...
8
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2answers
407 views

Is there a way to negotiate a secret between 2 parties with no prior knowledge?

Is there a way for 2 parties to negotiate a shared secret (for example, a session key) without having a pre-shared knowledge? SSL does this by using asymmetric encryption. Is there any other way to ...