Would iTunes Sync or iCloud Backup include app data for Kryptonite (possibly including the private key)?
1. iCloud backups are encrypted.
2. If you're not comfortable with #1, you can manually exclude an individual app from iCloud backups through Settings > Storace & iCloud Usage > Manage Storage (in the iCloud section). Click on your device in the Backups section. Turn off Kryptonite in the "Choose Data to Back Up" section.