LockDown Browser Digital Signature Error on Mac (Fix Guide)

Last updated 2026-05-02 · LDBypass Editorial

Why this error appears

Apple's code-signing chain requires the macOS Gatekeeper to trust:

1. The Apple Root CA (built into every macOS install).
2. The Apple Developer ID Intermediate CA (delivered via macOS updates).
3. Respondus's Developer ID Application certificate (signed by the intermediate).
4. The actual .app binary (signed by Respondus's cert).

If your macOS is too old, it doesn't trust the current intermediate CA. LDB's signature, which uses a recent intermediate, fails verification with "Digital signature error".

Affected macOS versions in 2026

The error specifically appears on:

• macOS Big Sur 11.0-11.3: Apple stopped pushing intermediate cert updates to these. Common on Macs that haven't updated since launch.
• macOS Monterey 12.0-12.4: same issue, less common.
• Older Ventura (13.0-13.2): rare but possible.
• Sonoma 14.x and Sequoia 15.x: unaffected - both have current trust.

Fix 1 - Update macOS to the current minor version

The reliable fix:

1. System Settings → General → Software Update.
2. If an update is available, install it. Apple's minor updates include intermediate CA refreshes.
3. Restart your Mac.
4. Retry the LDB install - the .dmg should now verify cleanly.

If your Mac is on macOS Monterey 12.0-12.4 specifically, the update path is to install Monterey 12.7 or later (the last security-supported Monterey release). System Settings shows the latest available update.

Fix 2 - Upgrade to a newer macOS major version

If your Mac supports a newer macOS (Ventura 13, Sonoma 14, Sequoia 15), upgrading is the more durable fix. About This Mac → System Report → Hardware → Model Identifier shows your Mac's model; Apple's compatibility list shows which macOS your Mac supports.

Don't do this 30 minutes before an exam - major upgrades take 30-60 minutes and may need post-install setup.

Fix 3 - Re-download the .dmg

Less commonly, the digital signature error is from a corrupted .dmg (Wi-Fi dropped during download, AV modified the file mid-transfer). Symptoms:

• The error happens consistently with one .dmg but a fresh download from the same LMS link works.
• The downloaded file size is meaningfully smaller than the LMS's expected size.

Solution: delete the .dmg from Downloads, re-download from your LMS link, retry install.

Fix 4 - Disable third-party antivirus during install

Malwarebytes, Bitdefender, Sophos, Norton occasionally modify .dmg files during their real-time scan, breaking the signature mid-process. Workaround:

1. Pause your antivirus product's real-time scanning. Most have a "pause for 1 hour" toggle in their menu bar.
2. Re-download the .dmg.
3. Install.
4. Re-enable antivirus afterward.

What does NOT fix this error

• Right-click → Open: doesn't bypass code-signing chain validation.
• Adding LDB to Gatekeeper exceptions: doesn't help if the cert chain itself fails verification.
• Disabling Gatekeeper entirely (spctl --master-disable): not recommended, requires admin, and the install still goes through code-signing checks.
• Re-running the same .dmg multiple times: same .dmg → same signature → same error.

How to verify your macOS trusts the current intermediate

# In Terminal:
security verify-cert -c /Applications/Some.app/Contents/_CodeSignature/CodeResources -L
# Or simpler - try opening any other notarised app's installer:
open ~/Downloads/some-other-notarised-app.dmg

If other notarised .dmg files also fail with similar errors, the trust issue is system-wide. macOS update is the universal fix.