The password you set when you set up E2EE on your first computer is the password you enter into all subsequent clients after they have synced for the first time. You will end up with one master key id and one password for all your clients.
I have added a bit of extra detail to the Joplin instructions.:
- On your first device (eg. on the desktop application), go to the Encryption Config screen and click “Enable encryption”
- Input your password. This process will generate a Master Key ID and the password you set will be used to encrypt all your notes. Make sure you do not forget it since, for security reasons, it cannot be recovered.
- Now you need to synchronise all your notes so that they are sent encrypted to the sync target (eg. to OneDrive, Nextcloud, etc.). Wait for any synchronisation that might be in progress and click on “Synchronise”.
- Wait for this synchronisation operation to complete. Since all the data needs to be re-sent (encrypted) to the sync target, it may take a long time, especially if you have many notes and resources. Note that even if synchronisation seems stuck, most likely it is still running - do not cancel it and simply let it run over night if needed.
- Once this first synchronisation operation is done, open the next device you are synchronising with. Click “Synchronise” and wait for the sync operation to complete. The device will receive the master key that was created at step 2, as part of the sync process. Go to the Encryption settings page on the new client where you will see a single Master Key entry with the same ID as at step 2, and you will need to provide the password for it. This is the password that you set at step 2. At this point E2EE will be automatically enabled on this device. Once done, click Synchronise again and wait for it to complete.
- Repeat step 5 for each device.