A telepathic firewall is a suite of protections around a mind to prevent casual scanning or attempts to penetrate into hidden thoughts. For some, this manifests as shields or walls while others view it as rooms and mazes.
Almost every natural telepath is capable of establishing a firewall, though the strength and resiliency of the the shield is depending on the telepaths themselves. Firewalls can also be set up to be passive, which means they function when the telepath is under duress, sleeping, or unconscious. It is just as difficult to peek into the mind of a sleeping telepath as it is to pry into a hostile one.
Casual Access
⚠️ SPOILER: From this point, this page reveals spoilers for Flight of the Scions. ⚠️ SPOILER: From this point, this page reveals spoilers for Desert Child.
A telepath can choose to give someone access almost immediately. In the example below, Tagon gave Kanéko the ability to query without resistance because he trusted her and knew that she wasn't capable.
She looked over at him, and then reached down to grab his hand. As soon as she felt the itch of his telepathy, she brought up the image of the gun. It came quickly, like with Ruben's knowledge. She focused on it. Images flashed through her head and she continued to pull the construction of the weapon, how to use it, and what it could do. The images burned through her thoughts and she used it to explode it into parts and reassemble it in her mind.
«Kanéko Lurkuklan, we need to discuss your manners with telepaths,» came the amused thought from Tagon.
— Flight of the Scions 42
On the other hand, when Kanéko meets up with Ojinkomàsu, access was not granted or even acknowledged despite the horse being intelligent and telepathic.
Kanéko opened her mouth, and then she felt a tickle of a presence in her mind. It was light and delicate, just like Ruben when he reached for her surface thoughts. She looked around sharply, looking for her friends or the waves of force that represented Damagar, but she couldn't see either. She didn't know if she should shield her thoughts or open up.
The tickle faded after a moment without another image.
— Flight of the Scions 40
Conditional Access
Shields do not have to be an all-or-nothing approach. Instead, there can be a system to allow some telepaths access to more than others. This is how much of the authorization of the kotim functions, though the shields are implemented as imprinted rules than the willpower behind the telepath.
This also means it is possible to break or hack into a kotim's authorization. This can be an easy or difficult task depending on the scope of the kotim, trying to break through the authorization layers of the votim would be an epic hurdle to say the least.
Passive Telepaths
Individuals without the ability to communicate telepathically are capable of establishing shields themselves. Since they can't perceive the telepathic communication, they usually need an active telepath to guide them but it is possible to create shields without any other assistance.
She brought up images of her designs, working through the mechanics when it hit her. She pictured them forming a shield—a wall of gears, pistons, and boilers. The force of Damagar's thoughts slammed into her chest, staggering her physically, but she could feel his questing probe crashing on her mental shield. Mental claws reached over her, but Kanéko brought up more images, combining the gears together and building it in her head with obsessive focus.
For a moment, she thought Damagar would still break through, but then the haze of the Jonahas root draped over her thoughts and the pressure subsided.
Kanéko found herself thinking about the pond they slept near two nights before. However, she could also picture Damagar standing in the pond, trying to track them down. She wasn't surprised when the image of the giant toad came through. It looked at her through her shield of gears. Dozens of personalities, all using the same crimson eyes, regarded her and something—the name Observation drifted through Kanéko's head—reached through the shield, pulling up memories of the land around her. No matter how hard Kanéko tried to obscure her thoughts with designs, she felt Damagar's Observation forcing her to recall the memories of her location: the path she had taken, the position of the sun, and even the route that they planned on taking.
— Flight of the Scions 30