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simple-notes-sync/docs/SELF_SIGNED_SSL.md

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Self-Signed SSL Certificate Support

Since: v1.7.0
Status: ✅ Supported

Overview

Simple Notes Sync now supports connecting to WebDAV servers with self-signed SSL certificates, such as:

  • ownCloud/Nextcloud with self-signed certificates
  • Synology NAS with default certificates
  • Raspberry Pi or home servers
  • Internal corporate servers with private CAs

How to Use

Step 1: Export Your Server's CA Certificate

On your server:

  1. Locate your certificate file (usually .crt, .pem, or .der format)
  2. If you created the certificate yourself, you already have it
  3. For Synology NAS: Control Panel → Security → Certificate → Export
  4. For ownCloud/Nextcloud: Usually in /etc/ssl/certs/ on the server

Step 2: Install Certificate on Android

On your Android device:

  1. Transfer the .crt or .pem file to your phone (via email, USB, etc.)

  2. Open Settings → Security → More security settings (or Encryption & credentials)

  3. Install from storage / "Install a certificate"

    • Choose "CA certificate"
    • Warning: Android will display a security warning. This is normal.
    • Tap "Install anyway"

  4. Browse to your certificate file and select it

  5. Name it something recognizable (e.g., "My ownCloud CA")

  6. ✅ Done! The certificate is now trusted system-wide

Step 3: Connect Simple Notes Sync

  1. Open Simple Notes Sync
  2. Go to Settings → Server Settings
  3. Enter your https:// server URL as usual
  4. The app will now trust your self-signed certificate ✅

Security Notes

⚠️ Important

  • Installing a CA certificate grants trust to all certificates signed by that CA
  • Only install certificates from sources you trust
  • Android will warn you before installation – read the warning carefully

🔒 Why This is Safe

  • You manually install the certificate (conscious decision)
  • The app uses Android's native trust store (no custom validation)
  • You can remove the certificate anytime from Android Settings
  • F-Droid and Google Play compliant (no "trust all" hack)

Troubleshooting

Certificate Not Trusted

Problem: App still shows SSL error after installing certificate

Solutions:

  1. Verify installation: Settings → Security → Trusted credentials → User tab
  2. Check certificate type: Must be a CA certificate, not a server certificate
  3. Restart app: Close and reopen Simple Notes Sync
  4. Check URL: Must use https:// (not http://)

"Network Security Policy" Error

Problem: Android 7+ restricts user certificates for apps

Solution: This app is configured to trust user certificates ✅
If the problem persists, check:

  • Certificate is installed in "User" tab (not "System")
  • Certificate is not expired
  • Server URL matches certificate's Common Name (CN) or Subject Alternative Name (SAN)

Self-Signed vs. CA-Signed

Type Installation Required Security
Self-Signed ✅ Yes Manual trust
Let's Encrypt ❌ No Automatic
Private CA ✅ Yes (CA root) Automatic for all CA-signed certs

Alternative: Use Let's Encrypt (Recommended)

If your server is publicly accessible, consider using Let's Encrypt for free, automatically-renewed SSL certificates:

  • No manual certificate installation needed
  • Trusted by all devices automatically
  • Easier for end users

Setup guides:

Technical Details

Implementation

  • Uses Android's Network Security Config
  • Trusts both system and user CA certificates
  • No custom TrustManager or hostname verifier
  • F-Droid and Play Store compliant

Configuration

File: android/app/src/main/res/xml/network_security_config.xml

<base-config>
    <trust-anchors>
        <certificates src="system" />
        <certificates src="user" />  <!-- ← Enables self-signed support -->
    </trust-anchors>
</base-config>

FAQ

Q: Do I need to reinstall the certificate after app updates?
A: No, certificates are stored system-wide, not per-app.

Q: Can I use the same certificate for multiple apps?
A: Yes, once installed, it works for all apps that trust user certificates.

Q: How do I remove a certificate?
A: Settings → Security → Trusted credentials → User tab → Tap certificate → Remove

Q: Does this work on Android 14+?
A: Yes, tested on Android 7 through 15 (API 24-35).

Related Issues

Need help? Open an issue on GitHub