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Faster and more secure TLS

Open Daniel Tang requested to merge danielt/kdeconnect-android:fast-secure-tls into master

Summary

On Telegram, it was discussed that KDE Connect is using a lot of CPU while sending/receiving files. I believe that this overhead comes from encryption, mostly outdated TLS ciphers.

I enabled and prioritized ChaCha20 for better performance. However, I didn't notice much of a difference before and after on my machines (the original problem didn't affect me either). I created this MR in hopes that it would improve performance for others.

Misc

I also disabled TLS 1.1 and below as they are vulnerable and deprecated. To avoid 0-RTT and minApi problems, I didn't enable TLS 1.3. This means that TLS 1.2 is the only version enabled now (unfortunately, I had to raise the minimum Android version to 4.4.4 for this).

I removed the ECDSA ciphers that were doing nothing (we only have an RSA certificate). I wanted to remove TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA as it was outdated, but did not because of backwards compatibility for LTS desktop versions.

Benchmarks

These are benchmarks of this patch. I doubt this will show much, since I've already said that this patch doesn't make much of a difference for me. See Telegram for the screenshots from the user who is affected by this problem.

Android -> KDE, Before

receiveBefore

Android -> KDE, After

receiveAfter

KDE -> Android, Before

sendBefore

KDE -> Android, After

sendAfter

Test Plan

All of the following:

  • At least one user must notice a significant performance improvement when sending/receiving files
  • It must be possible to connect to the same peers as before this patch
  • There shall be no visual or behavioural changes
Edited by Daniel Tang