The different permissions that you can grant to a device or backend application to access your IoT Hub are:

• iothubowner: This will allow any device or backend solution all permissions
• service: This will allow an access policy with only the Service connect permission
• device: This will enable the device with an access Policy which has the Device connect permission
• registryRead: This is a policy with Registry read permission
• registryReadWrite: This is a policy with Registry read and Registry write permissions
• Per-device security credentials: Each device's credentials are maintained in the device registry