27 votes
Accepted

How can we exchange public keys between two servers in a secure way?

This will mean a lot of unneeded overhead. I'd suggest following: Since you don't have certificates issued by CA, create your own CA. Namely, create a self-signed certificate and add it to a key ...
mentallurg's user avatar
  • 12.4k
18 votes

Can a large corporation make a believable promise

However, if the third party makes a secret copy, then they can covertly sell it for large amounts of money. The thing about this is when it comes to a pivotal and highly-valued asset such as said key,...
mallocation's user avatar
  • 1,676
16 votes
Accepted

Can a large corporation make a believable promise

Companies make promises they can't renege on all the time - that's what a contract is. After all, insurance wouldn't exist if an insurer could wriggle out of paying claims through things like secret ...
mjt's user avatar
  • 415
13 votes
Accepted

Forward secrecy with GnuPG

Is there anything like this? There is actually a draft specifically on doing this, titled Forward Secrecy Extensions for OpenPGP. The gist of the draft is that temporary keys must be created for each ...
forest's user avatar
  • 66.7k
13 votes

How can we exchange public keys between two servers in a secure way?

No, I don't think that the solution is good. Let’s go through it: This is fine If we can manually copy, why not copy the public keys directly? Here's the real problem. As this is done on an insecure ...
tim's user avatar
  • 29.6k
11 votes

"Diffie-Hellman Key Exchange" in plain English

Securing data as it passes through the internet usually requires protecting it in two ways: Confidentiality -- assuring no one except the intended recipients can read the data Integrity -- assuring ...
Eddie's user avatar
  • 781
9 votes
Accepted

Why does TLS 1.3 deprecate custom DHE groups?

With TLS 1.2 the server first needed to tell the client within the ServerKeyExchange message about the parameters of the DHE group it supports. Only then the client could act on these. With TLS 1.3 ...
Steffen Ullrich's user avatar
9 votes

Can a large corporation make a believable promise

How could the company show that it instructed the employees to destroy the key? Easy. When an employee was instructed, he/she signs a document that he/she was instructed and understood fully the ...
mentallurg's user avatar
  • 12.4k
8 votes
Accepted

Is symmetric encryption with one time pre-shared key secure?

Basically, no. You haven't even gone half way towards describing your system. Will you be using a stream cipher or a block cipher? How will you authenticate this traffic? How will you protect it from ...
r3mainer's user avatar
  • 875
8 votes

Is it possible to run out Public-Key servers' storage by sending them countless valid Public-Keys?

This question really just boils down to, "Should you put rate-limits on a public-facing endpoint that accepts and records uploaded data from untrusted users?", to which the answer is virtually always "...
Stephen Touset's user avatar
8 votes
Accepted

Is a certificate with more bits than its parent more secure?

Neither 2048 nor 4096 bit RSA can currently be broken. Thus the question is how it affects the security of the data if the attacker sniffs the data today but manages to break the keys in the future: ...
Steffen Ullrich's user avatar
8 votes

SSH key based login is not vulenerable to MiTM attack. Is it true?

First, a man in the middle attack can neither happen with key based nor with password based authentication if the client properly authenticates the server. A man in the middle attack is possible if ...
Steffen Ullrich's user avatar
8 votes
Accepted

ECDH and static key encryption

Your understanding is broadly correct, but in security and especially in cryptography, “broadly correct” often doesn't cut it. There is a standard for encryption using elliptic curve cryptography to ...
Gilles 'SO- stop being evil''s user avatar
8 votes

Can a large corporation make a believable promise

I am not sure I completely understood your question, but technically speaking you may want to use an encryption method which distributes the key to several parties, and all must be present in order to ...
WoJ's user avatar
  • 9,038
7 votes
Accepted

Is it secure to share a public (RSA) key over http?

TL;DR: No. "Secure" is not a binary property, and this is better than nothing, but it's very vulnerable to MitM. What you're describing is effectively unauthenticated opportunistic ...
CBHacking's user avatar
  • 48.4k
7 votes
Accepted

TLS 1.3 RSA key exchange

I've always thought that a server's TLS x509 certificate was passed to the client and certificate was used to encrypt traffic between client and server This approach isn't widely in use anymore since ...
user272480's user avatar
6 votes
Accepted

Role of the chosen ciphersuite in an SSL/TLS connection

So from what I understand it generally works like this: Client connects to the server For HTTPS yes. For other applications it varies; some make a new connection and some reuse an existing ...
dave_thompson_085's user avatar
6 votes
Accepted

Tor: Is a Diffie-Hellman key exchange being done over recipient of traffic?

No, the key exchange is done between the client and each relay. This is the general technique behind onion routing. For the modern Tor protocol, the client will exchange a symmetric key (AES128) with ...
forest's user avatar
  • 66.7k
6 votes
Accepted

Can we trust onetimesecret?

Key exchange is routinely done without using external services, by using cryptography. The most popular key exchange algorithm is Diffie-Hellman. Quoting Wikipedia: The Diffie–Hellman key exchange ...
A. Darwin's user avatar
  • 3,582
6 votes

How can we exchange public keys between two servers in a secure way?

The only way to establish initial trust between two servers separated by an untrusted network has to involve a manual1 step. This can be achieved either by copying it manually or by manually comparing ...
Hubert Jasieniecki's user avatar
6 votes
Accepted

Is it possible to use HKDF in the TPM?

If it isn't in the spec it isn't in there. The question is if you need it if e.g. the NIST SP 800-108 KDF in counter mode is present. That's a fine KDF even if it lacks explicit extract / expand steps ...
Maarten Bodewes's user avatar
5 votes
Accepted

SSL protocol analysis

I sneakily edit a sneaky MITM attacker into your image: The problem with this protocol is that Bob does not authenticate with Alice. That means a man-in-the-middle attacker who can manipulate the ...
Philipp's user avatar
  • 49.4k
5 votes
Accepted

How to test TLS handshake process?

I don't know if this is the best channel to ask, however - this is how I do it. Simple information: openssl s_client -state -nbio -connect myhost:443 If you need a deeper insight, you may want to ...
gusto2's user avatar
  • 286
5 votes

What is the the meaning of "out-of-band" in "out-of-band key exchange"?

From Wikipedia: Out-of-band is activity outside a defined telecommunications frequency band, or, metaphorically, outside some other kind of activity. It just means through another means of ...
Anders's user avatar
  • 65.6k
5 votes

How does "Key Transparency" work?

Key Transparency makes it possible for users to know about all the public keys that are in the user's account, preventing the server from adding public keys to a user's account without detection. Key ...
Gary Belvin's user avatar
5 votes

Can we trust onetimesecret?

What is the better alternative to exchange a key? Better in what way? Security? Simplicity? In the case of security, have multple methods of key transmission. For example, give 10 characters ...
jvkbzowtb's user avatar
  • 169
5 votes
Accepted

Can password strength be enforced with PAKE protocols?

No, you can't enforce a client-side policy via technical means. As you mention, any limits you bake into an implementation could be bypassed by someone using a modified client. But that presumes you ...
John Deters's user avatar
  • 34.2k
5 votes

How can I verify Keybase's end-to-end encryption between me and a friend?

Keybase's chat in the app was never verifiably end-to-end encrypted. The first time you talk to someone, it downloads their encryption key from the Keybase server and you have to trust the server to ...
Luc's user avatar
  • 32.9k
4 votes
Accepted

What are the requirements for private keys in Diffie-Hellman key exchange algorithm

IF (that's a big "if") the generator g and the public element from the peer can be assumed to be part of a subgroup of prime order, THEN it suffices for exponents to have size 2t bits, for a "security ...
Thomas Pornin's user avatar
4 votes

Diffie Hellman Key Exchange in a messaging application

To get a good picture of the Diffie Hellman Key Exchange some diagramatic representations may be helpful. The common approach for messaging applications on Android (or any other client devices) in ...
Douglas Daseeco's user avatar

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