A keyboard I recently installed on iOS 8 provides an option (in Settings) to "Allow Full Access"?
What does this setting do?
"Allow Full Access" has nothing to do with using the actual keyboard. The keyboard is accessible for you to use throughout the system regardless of this setting. In short, allowing full access grants the developer of the keyboard additional access to some of your information and gives the developer access to the internet. From the technical specifications under "Designing for User Trust", Allow Full Access does this:
The second bullet point is what Apple really wants you to understand. With Allow Full Access a developer COULD send your keystrokes to their server for processing, which might include:
Apple is highlighting the fact that a developer COULD use your keystrokes for nefarious reasons instead of the legitimate reasons I listed above. It is possible for a developer to record your sensitive information such as credit card number or street address.
In my opinion, it is not possible for a developer to write a fully-fledged keyboard extension without requesting full access. Without Full Access I can't utilize In-App Purchases, I can't sync your preferences using iCloud, I cannot even provide a basic auto-correct feature.
I just finished developing a keyboard extension for iOS. My keyboard never sends your keystrokes across the internet. I will never see what you have typed. There are no privacy concerns in my opinion, yet you still receive a scary message from Apple when you turn on Allow Full Access. If you have concerns about turning Allow Full Access ON, ask the developer how they are using your data/keystrokes.
One additional note, you cannot use a custom keyboard to type into a password field. iOS will always use the system keyboard for password fields. Developers that do process your keystrokes will not have access to your passwords, unless you type your passwords into a non-password field.
If you try it it will inform you of this:
Users can tap the keyboard name from here and check a box for "Allow Full Access." Doing so presents the user with another prompt that reads:
"Full access allows the developer of this keyboard to transmit anything you type, including things you have previously typed with this keyboard. This could include sensitive information such as your credit card number or street address."
If the user chooses to accept this prompt and allow the keyboard, it can now be accessed systemwide. When the virtual keyboard pops up, simply tap the globe icon in the bottom left corner to cycle through available keyboards, or hold down on the icon to pop up a list.