I suggest looking at the apps and tools developed by the Guardian Project <a href="https:&#x2F;&#x2F;guardianproject.info&#x2F;code&#x2F;" rel="nofollow">https:&#x2F;&#x2F;guardianproject.info&#x2F;code&#x2F;</a><p>There was an encrypted note-taking app but it&#x27;s not developed any more.<p>The generic solution is to use GnuPG.