The Notes.app is great on iOS, but it may not be the best app to input personal information.
While the standard Notes.app can be password locked with certain jailbroken utilities, Codebook is an app that locks your notes without jailbreaking.
Codebook by Zetetic
Codebook is a highly rated secure and encrypted notebook application. The app is essentially a notes app that password protects your notes, whether those be ideas, general notes, or personal information.
If you ever keep your iPhone unattended, Codebook keeps your information secure!
The app features 256-bit AES Encryption and secure password protection (user defined). Once a note is created, users have full text searching, the ability to copy/paste between apps, and are able to email notes directly from within the app.
Codebook also auto-saves notes to avoid data loss if a note taking session is interrupted.
In other words, Codebook has a very native look and feel to the standard Notes.app but has many new and secure features that are not available in the standard iOS app. If you’re looking for a highly rated, password-protected notes app, Codebook is available in the App Store for $2.99.