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Secure Integrated Sensing and Communication: Information Theory Offers Insights

This paper surveys information-theoretic approaches to secure Integrated Sensing and Communication (ISAC) systems, organizing existing literature by adversary models and protected functionalities while analyzing the fundamental tradeoffs between communication reliability, sensing performance, and security.

Original authors: Truman Welling, Onur Günlü, Aylin Yener

Published 2026-05-12

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Truman Welling, Onur Günlü, Aylin Yener

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are trying to do two things at once with a single flashlight: you want to talk to a friend across the room, and you also want to scan the room to see if anyone is hiding in the shadows. This is the core idea of Integrated Sensing and Communication (ISAC). Instead of using one flashlight for talking and a separate one for scanning, you use the same beam for both.

This paper is a "survey" (a big review) of the math and theory behind making this dual-purpose flashlight secure. It asks: How do we make sure our friend hears us clearly and sees the room, while making sure a sneaky spy neither hears our secret message nor figures out where the hidden people are?

Here is a breakdown of the paper's main ideas using simple analogies:

1. The Two Jobs of the Flashlight

In a normal world, we usually separate these jobs. But in this new technology, the signal sent out does double duty:

Communication: It carries a message (like a text or voice).
Sensing: It bounces off objects (like a radar) to tell us about the environment (like "there is a car 50 meters away").

The Problem: Because the same signal does both jobs, a spy listening in might learn two dangerous things:

They might decode your secret message.
They might use the signal to figure out where you are looking or what you are sensing (e.g., "Oh, they are scanning for a specific type of car, so that car must be there").

2. The Two Types of Spies

The paper divides the bad guys into two categories:

The Passive Spy (The Eavesdropper): This person is like a ghost. They just sit in the corner, listening to the signal and watching the reflections. They aren't trying to stop you; they just want to steal information.
- The Goal: Make sure the spy can't understand your message or can't guess what you are sensing.
The Active Spy (The Jammer): This person is like a bully with a megaphone. They don't just listen; they shout over you or throw dirt in your flashlight beam to mess up your vision.
- The Goal: Make sure you can still talk and see clearly even while they are trying to ruin your day.

3. The Magic Trick: Using the Echo as a Secret Key

One of the paper's most interesting findings is that sensing can actually help with security.

Imagine you are talking to your friend, and you hear an echo bounce off a wall. That echo tells you something about the room.

The Paper's Insight: Because you (the transmitter) hear the echo, you know something about the environment that the spy (who is standing somewhere else) does not.
The Analogy: It's like having a secret handshake that only works because you both know the room is windy. The paper shows that by analyzing these "echoes" (sensing feedback), the transmitter can generate secret keys to lock the message, making it harder for the spy to crack, even if the spy has a very good microphone.

4. Two Different Types of "Secrets"

The paper points out that protecting a message is different from protecting a "sensing" result.

Protecting the Message (Secure Communication): This is like hiding a letter. You want the spy to see the envelope but not be able to read the words inside.
Protecting the Sensing (Secure Sensing): This is like hiding what you are looking at. Imagine you are taking a photo of a secret location. You don't just want to hide the photo; you want to make sure the spy can't look at the photo and guess, "Oh, they were looking at the bank vault."
- How to do it: The paper suggests you might intentionally add "ghosts" or fake targets into the signal. To your friend, the real target is clear. To the spy, the image is blurry and full of fake targets, so they can't tell what's real.

5. The "Covert" Mode (The Invisible Flashlight)

There is a special case called Covert ISAC.

The Goal: Not only do you want to hide the message, you want to hide the fact that you are even talking.
The Analogy: It's like whispering in a crowded room so quietly that the person next to you doesn't even realize you are speaking. In this scenario, the system tries to sense the environment without anyone noticing that a signal was sent at all.

6. The Big Trade-Off

The paper explains that you can't always have everything perfect.

If you make the signal very strong to see clearly (good sensing), it might be easier for the spy to hear you (bad security).
If you scramble the signal to hide it from the spy (good security), your friend might have a harder time understanding it or seeing the targets clearly.

The math in the paper tries to find the "sweet spot" where you get enough security without ruining your ability to talk or see.

Summary

This paper is a map for engineers. It says: "We are building systems that talk and see at the same time. Here is the math on how to keep those systems safe from spies who are just listening, spies who are shouting, and spies who are trying to guess what we are looking at. It turns out that the act of 'seeing' (sensing) can actually help us 'hide' (secure) our messages better than we thought."

Technical Summary: Secure Integrated Sensing and Communication: Information Theory Offers Insights

Problem Statement
Integrated Sensing and Communication (ISAC) unifies sensing and communication within a shared system framework using a single transmitted signal. While this integration improves spectral and hardware efficiency, it introduces novel security challenges distinct from traditional secure communication. Specifically, the dual use of the signal creates new leakage mechanisms: users associated with one function (e.g., sensing) may inadvertently infer information related to the other (e.g., communication), and vice versa. Furthermore, the sensing target itself may act as an unauthorized node capable of gathering sensitive information about the transmitted message. The paper addresses the need to jointly model communication reliability, sensing performance, and security to understand the fundamental tradeoffs inherent in these systems.

Methodology
The paper adopts an information-theoretic perspective to survey and analyze secure ISAC models. Rather than reviewing specific engineering architectures or algorithmic designs, the authors focus on fundamental limits, channel models, and performance metrics. The methodology involves:

Categorization: Organizing existing literature based on the protected functionality (message vs. sensing state) and the adversary model (passive vs. active).
Model Abstraction: Utilizing a unified notation where a transmitter sends inputs $X^n$ to a legitimate receiver ( $Y_1^n$ ) and an unauthorized node ( $Y_2^n$ ). Sensing is modeled via a state sequence $S^n$ and feedback $Z^n$ (in monostatic setups) or a separate receiver.
Metric Definition: Defining performance in terms of communication rate, secure rate, sensing distortion (or inference error), and information leakage (measured via mutual information or variational distance).
Comparative Analysis: Examining how different assumptions—such as noncausal state knowledge, causal feedback, transmitter actions, and the location of the sensing antenna (monostatic vs. bistatic)—alter the achievable tradeoff regions.

Key Contributions and Results
The paper synthesizes the current state of information-theoretic secure ISAC, highlighting several key findings:

Secure Communication with Sensing Feedback:
- In models where the transmitter receives feedback (e.g., reflections in monostatic ISAC), sensing can actively enhance secure communication.
- The authors detail how feedback allows for the extraction of secret keys or the creation of additional secrecy resources beyond traditional wiretap coding.
- Results show that in physically degraded channels, secrecy can be achieved entirely through secret-key extraction from sensing feedback, even if the legitimate receiver does not have a channel advantage over the eavesdropper.
- Specific models (e.g., [3], [9], [16]) characterize the tradeoff between communication rates and state-estimation distortion, showing that sensing-enabled feedback can enable secure communication in regimes where it would otherwise be impossible.
Secure Sensing:
- Unlike communication security, which aims to hide a message, sensing security aims to degrade an unauthorized node's ability to estimate the environmental state or target parameters.
- This is formulated as an estimation-theoretic problem, often constrained by a lower bound on the distortion between the unauthorized node's reconstruction and the true state.
- Approaches include limiting unauthorized reconstruction quality via distortion constraints or introducing "ghost targets" through waveform engineering to create ambiguity for the adversary.
Active Adversaries:
- The paper reviews models where adversaries actively interfere (e.g., jamming).
- Results indicate that secure ISAC in these settings becomes a joint robustness and adaptation problem. Strategies include game-theoretic beamforming (Stackelberg games) and the use of Reconfigurable Intelligent Surfaces (RIS) to co-design communication, sensing, and infrastructure placement against attacks.
Synergies and Interactions:
- Joint Protection: Some formulations simultaneously protect the message and the state, revealing that the coupling between these objectives depends heavily on whether the state is known noncausally or inferred via feedback.
- Privacy vs. Security: The paper distinguishes between sensing security (preventing unauthorized inference) and privacy (potentially limiting what even authorized entities can infer about user-sensitive states).
- Covert ISAC: In covert settings, the objective includes preventing a warden from detecting the presence of communication. The paper notes that for specific binary input alphabets, there may not be a tradeoff between covert communication rate and sensing performance.

Significance and Claims
The paper positions itself as a tutorial that clarifies the fundamental limits of secure ISAC, separating common modeling frameworks from specific paper results. Its primary significance lies in:

Establishing a Unified View: It demonstrates that sensing is not merely an auxiliary function but can actively contribute to enabling secure communication through feedback and environmental inference.
Clarifying Tradeoffs: It highlights that the tradeoffs among communication reliability, sensing performance, and security are intrinsic to the dual functionality of ISAC, rather than artifacts of specific algorithms.
Identifying Gaps: The authors modestly note that while foundational results exist for memoryless channels with idealized feedback, significant open directions remain. These include multi-transmitter/receiver systems, generalized feedback models tailored to practical ISAC, the role of time-varying channels, and the extent to which inherent channel properties can provide security without relying on large amounts of pre-shared randomness.

The paper concludes that information theory is essential for identifying which security-sensing tradeoffs are fundamental and which are design-dependent, providing a baseline for future engineering and algorithmic developments.