I rediscovered a gem by former ATPM staffer Kirk McElhearn from the June 2004 issue of Macworld. In the Working Mac column, Kirk is discussing built-in ways to protect data in Mac OS X. I found the use of the Keychain as a storage place for secret notes intriguing.
To turn Keychain into your security guard, open Keychain Access (Applications: Utilities), and click on Note in the Keychain Access toolbar. Enter a descriptive title in the Name field of the window that appears, and then type or paste the data you want to protect into the Note field. You’re not limited to short things, such as a password or a credit card number. I pasted several megabytes of text into one secure note.
To access your secure notes later, open Keychain Access, find the note in the list of protected items, and click on its name. Select the Show Password option and enter your password; you’ll then see the note’s contents. To enter the contents in another program, click on Copy Note To Clipboard, enter your password again, and paste into any text field or document.