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 ...
- 12.5k
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,...
- 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 ...
- 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 ...
- 67.1k
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 ...
- 29.7k
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 ...
- 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 ...
- 206k
9
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 ...
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 ...
- 12.5k
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 "...
- 5,804
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:
...
- 206k
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 ...
- 206k
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 ...
- 9,078
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 ...
- 50.3k
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 ...
- 86
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 ...
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 ...
- 67.1k
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 ...
- 3,567
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 ...
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 ...
- 4,798
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 ...
- 65.7k
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 ...
- 61
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 ...
- 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 ...
- 34.6k
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 ...
- 33.1k
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 ...
- 634
4
votes
SSH key based login is not vulenerable to MiTM attack. Is it true?
When you are using private/public key authentication and agent forwarding, a full ssh mitm attack is still possible. Agent forwarding is a security issue and should not be used.
In cases, when agent ...
- 1,482
4
votes
TLS protocol, session key for secure connection
is the public key sent by server encrypted or clear? I assume it is clear since it is public
The public key of the server is contained in clear in the server certificate which is send in clear by the ...
- 206k
4
votes
Is it a good idea to use asymmetric encryption for a chat application?
Yes, there's a reason; public key encryption is very slow and CPU-intensive, and not at all suitable for encrypting chat data, which may well include images, audio or video as well as text. That's why ...
- 10.3k
4
votes
Why is the Diffie-Hellman exchange not enough to authenticate the communication partners in IKE_SA_INIT?
The plain ephemeral (new key every connection) Diffie-Hellman is unauthenticated. You perform the DH operation using newly created keys on both sides and establish a shared secret value you can use to ...
- 8,564
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