Score:0

Crypto

How to use symmetric encryption on 1on1 and group chat messenger?

Kim San

9/12/23, 12:17 PM

Hi everyone so currently I'm trying to learn about encryption to build secure messaging app (Mobile-app, flutter based). I want the app to have 2 messaging features which are 1 on 1 messaging and group-chat messaging. Firstly I wanted to try using symmetric encryption for the app, but there are some question that make me a little bit confused:

1. When using symmetric encryption, assuming that each user have their own key. When Person A send message Person B should we fetch the person A key or person B key for the encryption ?

2. What's the best practice to store the user key ? can I just generate the key and keep it in the cloud database ?

3. Can I do like some double AES algorithm for the encryption? So the potential hacker will have to do more work for altering the system (1 main app Key, 1 user key)

4. How does symmetric encryption work for group chat messenger ? I don't get the flow logic

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aes

public-key

symmetric

Eugene Styer

9/12/23, 2:30 PM

Any reason that TLS (transport-layer security, sometimes called SSL) won't handle your situation?

Kim San

9/12/23, 2:32 PM

how does SSL help with my current situation ? can you explain it to me please ?

Eugene Styer

9/12/23, 4:42 PM

TLS provides security (the "S" in "HTTPS" for example) between a client and a server. If you are using a central server, get a certificate for your server, and TLS handles all the details of encryption between the client and server. You would just need to handle the username/password for A and B. The private key corresponding to the public key in the certificate needs to be secret, but not much else. If you want A to send messages directly to B (peer-to-peer networking) then treat A as the client and B as the server. Again TLS will handle the rest of the details.

Jake Peralta

9/12/23, 5:27 PM

Just for clarification of @KimSan as you're learning encryption, in Symmetric encryption key used by both users will be same. So you need different key for each conversation but not for user.

Score:0

Crypto

Lev

9/17/23, 12:10 AM

Here are some resources which might help you understand your problem.

This kind of use-case lends itself to the use of public key cryptography. Secure messaging protocols of this form already exist - see the Signal protocol.

If you are insistent on using symmetric key encryption. See the Kerberos protocol, which is a solution to your first two questions.

Can I do like some double AES algorithm for the encryption? So the potential hacker will have to do more work for altering the system (1 main app Key, 1 user key)

There are many answers to this question. For instance, here.

How does symmetric encryption work for group chat messenger ? I don't get the flow logic

This is not a trivial thing to construct. This is a brief video which explains why.

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Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: How to use symmetric encryption on 1on1 and group chat messenger?

TH: จะใช้การเข้ารหัสแบบสมมาตรบน 1 ต่อ 1 และแชทกลุ่มได้อย่างไร

RO: Cum să utilizați criptarea simetrică pe 1on1 și pe messengerul de chat de grup?

RU: Как использовать симметричное шифрование в мессенджере 1 на 1 и групповом чате?

VI: Làm cách nào để sử dụng mã hóa đối xứng trên 1 trên 1 và trình nhắn tin trò chuyện nhóm?

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