Encrypting transcript history: what it protects, and what it doesn't

16 August 2026 · 2 min read · Muteeb Mehraj

Encryption claims are easy to make and hard to evaluate, because the interesting part is never the algorithm. It is which attacks the design actually stops.

The problem

A dictation app that keeps history is keeping the most sensitive text you produce. Not a summary of it: the literal words, including the message you thought better of and deleted, the password you spoke aloud once by mistake, and the medical question you asked before rewording it.

The default place to put that on macOS is UserDefaults, which is a plist under your home directory. Readable by any process running as you, and by anyone with access to the disk. That is fine for a window position and wrong for this.

What Bellow does

History is encrypted with AES-GCM, an authenticated cipher, so tampering is detectable rather than merely difficult.

The key is generated once and stored in the macOS Keychain with two attributes that matter more than the cipher choice:

• kSecAttrAccessibleWhenUnlockedThisDeviceOnly. The key is only available while the Mac is unlocked, and it never leaves the device. It is excluded from encrypted backups that could be restored elsewhere.
• kSecAttrSynchronizable = false. It never goes to iCloud Keychain, so it does not propagate to your other devices.

The ciphertext lives in UserDefaults as before. Without the key it is bytes.

What this stops

Disk extraction. Someone with your drive, or a Time Machine backup, or a cloned volume, gets ciphertext. The key is not on the disk in a usable form and is marked non-transferable.

Casual inspection. Backup tools, sync utilities, migration assistants and anything else that walks ~/Library/Preferences sees an opaque blob rather than your dictation history.

Accidental exposure. Screen-sharing your preferences folder, or handing a diagnostic bundle to someone, does not hand over your transcripts.

What this does not stop

This is the part usually left out.

Malware running as you. If something is executing under your user account while your Mac is unlocked, it can ask the Keychain for the key exactly as the app does. No application-level encryption survives this, and any product implying otherwise is overselling. Your defences there are the sandbox, code signing and not running untrusted software.

Someone at your unlocked Mac. They can open the app and read the history in the interface. Encryption at rest is not a lock screen.

Anything after the text leaves. Dictated text is pasted into other applications, and those have their own storage, their own sync and their own logging. The clipboard in particular is readable by any running process and is not something a dictation app can secure on your behalf.

The honest summary

This protects the file. It does not protect a compromised account or an unattended machine. Those need different tools, and no amount of AES changes that.

If your threat model includes a compromised account, do not keep history. Bellow has a setting that stops writing text to disk entirely: counters still update so your stats work, but nothing you say is stored anywhere. That is a stronger guarantee than any encryption, because the safest data is the data that was never written.