Keyless Communication Achievements

• Keyless communication is a set of protocols that achieve secure data transfer without traditional keys, leveraging physical, quantum, and information-theoretic methods.
• It integrates diverse techniques such as wiretap coding, one-message authentication, and PUF-based encryption, applicable in IoT, automotive, and quantum channels.
• Practical results include high secure rates, low-latency authentication and robust protection against eavesdropping, even in resource-constrained environments.

Keyless communication refers to cryptographic and physical-layer protocols that achieve authentication, confidentiality, or secure channel establishment without reliance on pre-shared symmetric keys, certificates, or public-key primitives. This paradigm leverages information-theoretic, physical, quantum, and device-specific resources to attain security properties even when all computational secrets are absent or exposed. Modern keyless schemes span a broad range of approaches, including wiretap coding, physical unclonable functions (PUFs), context-based pairing, quantum state transmission, and protocol-level techniques for one-message authentication. The recent literature demonstrates these methods achieving strong security and high practical performance across constrained IoT, automotive, mobile, and free-space quantum communication domains.

1. Information-Theoretic and Multipath Keyless Communication

The multipath communication model pioneered in "Multipath Private Communication: An Information Theoretic Approach" (Ahmadi et al., 2014) formalizes conditions for keyless private message transmission (PMT) solely exploiting network diversity (e.g., frequencies, routes). It considers $n$ disjoint paths, with Alice and Bob able to simultaneously access up to $t_a$, $t_b$ paths, while an unbounded eavesdropper (Eve) can tap $t_e$ paths per transmission interval of $\lambda$ bits.

Two main secrecy notions arise:

• Perfect PMT (P-PMT): No error or leakage, achievable iff $t_e < t_{ab} = \min(t_a, t_b)$. Achievable rate approaches $1-t_e/t_{ab}$.
• Asymptotically-Perfect PMT (AP-PMT): Arbitrarily small error and leakage as message length grows, feasible for two-way interactive protocols whenever $t_e < n$, even if $t_a = t_b = 1$ and $t_e = n-1$. AP-PMT rates can approach $1-t_e/n$.

AP-PMT constructions rely on a hybrid "two-block" scheme: a coordination key is shared at low rate, then used to secretly choose transmission paths for a high-rate, secret-sharing-based scheme. This yields practical keyless, information-theoretic secrecy rates (e.g., 17% for frequency-hopping at 60 GHz, 20% for multi-route mobile ad-hoc networks) with no cryptographic key material (Ahmadi et al., 2014).

2. Keyless Authentication and One-Message Protocols

Keyless communication encompasses unforgeable authentication and integrity protocols that are robust even when the adversary knows protocol codebooks and input messages. In "Keyless authentication in the presence of a simultaneously transmitting adversary" (Graves et al., 2016), authentication is achieved in a discrete-memoryless multiple access channel (MAC) without any secret at all.

The construction relies on a randomized codebook using an auxiliary variable $U$ to encode messages; Bob detects intrusions by checking if only one message yields a "typical" output sequence, otherwise declaring an attack. Achievable rates are characterized by the mutual information $I(Y;U|V=\emptyset)$ where no simulatable attack to mimic the honest output distribution exists. A positive authentication rate is demonstrated, providing information-theoretic authenticity in the face of a fully informed, concurrently-transmitting adversary with no pre-shared secret (Graves et al., 2016).

For remote keyless entry and access control, the LASER protocol (Daza et al., 2019) achieves one-message authentication. It replaces typical multi-message rolling codes with a protocol where a key fob transmits a hash of a secret and timestamp; the vehicle verifies freshness and authenticity. A lightweight hash (e.g., Blake2s, $n \geq 48$ bits) underpins security, yielding negligible chance of forgery ($q_H/2^n$). Integrated frequency hopping thwarts jamming attacks. LASER's prototype demonstrates energy-efficient, sub-200 ms latency unlocking in active and passive RKE modes without symmetric block ciphers or public keys, significantly lowering hardware complexity in the key fob (Daza et al., 2019).

3. Physical Unclonable Functions and Hardware Keyless Schemes

Physical-layer entropy sources and physical fingerprints afford strong keyless properties for authentication and encryption. "Hardware Implementation of Keyless Encryption Scheme for Internet of Things Based on Image of Memristors" (Mohammadinodoushan, 2020) implements a full keyless encryption protocol on a commercial ARM microcontroller, replacing stored secret keys with on-demand responses from a memristor-based PUF lookup table (LUT). During "enrollment," parties measure and store a table of device-unique resistances; future sessions derive ephemeral secrets from orchestrated hash digests and PUF challenges, never storing or reusing any secret key material.

Authentication and encryption operations involve parallel hash iterations (via SHA-256 hardware), PUF lookups, and lightweight ciphering, achieving $\approx$6.4 kb/s throughput at $<$20 ms per authentication, all with millijoule-scale energy budgets on resource-constrained IoT hardware. The approach is inherently resilient against physical attacks on stored keys; all secrets are session-dependent and unrecoverable from device memory (Mohammadinodoushan, 2020).

4. Context and Reciprocity-Based Keyless Pairing

Secure device pairing without user interaction or pre-shared keying is achieved by extracting entropy from the physical environment or signal properties. InaudibleKey (Xu et al., 2021) uses channel reciprocity in the acoustic domain: two devices exchange and measure OFDM-probed acoustic signals in the 18–22 kHz regime, quantize the reciprocal channel frequency responses into bitstrings, and reconcile key mismatches via compressed sensing and privacy amplification. Such protocols deliver keyless key agreement at 768 bits/s rates, with secure pairing distances up to 220 cm, and robust protection against eavesdropping (attack success probability $<10^{-65}$ for a 128-bit key).

Sensor fusion and error correction minimize false acceptance rates, outperforming even radio or other sensor-based pairing (up to $145\times$ faster, $44\times$ longer range compared to prior works). The design is amenable to deployment on low-cost microcontrollers and smartphones (Xu et al., 2021).

FastZIP (Fomichev et al., 2021) advances zero-interaction pairing (ZIP), leveraging fuzzy PAKE across quantized and fused sensor signals (acceleration, gyroscope, barometer) combined with error-correcting codes. This enables threefold reductions in secure pairing time (e.g., down to 20–40 s), offline attack resistance, and empirical false acceptance rates below 0.5%, establishing new practical standards for keyless pairing of co-located IoT devices (Fomichev et al., 2021).

5. Quantum Keyless Private Communication

Quantum keyless protocols enable information-theoretic security for direct message transmission over quantum channels without the need for classical key distribution. In "Quantum Keyless Private Communication under intense background noise" (Mendes et al., 12 May 2025) and "Quantum Keyless Private Communication with Decoy States for Space Channels" (Vazquez-Castro et al., 2024), classical bits are encoded as quantum states (e.g., coherent pulses for OOK, phase-encoded for BPSK), and security is provided by the quantum wiretap model: an unauthorized eavesdropper is physically constrained to only a fraction $\gamma$ of the channel transmissivity.

Secrecy capacities per channel use are of the form $C_s = I(A;B) - I(A;E)$, where $I(A;B)$ and $I(A;E)$ are the mutual informations for the legitimate receiver and eavesdropper, respectively, under optimal measurement. In the OOK case, Helstrom error rates capture Eve's best discrimination. Advanced protocols introduce decoy/dummy states: Alice randomly interleaves optimized dummy states into the transmission, minimizing Eve's information even when $\gamma$ approaches $0.99$ or more, and thus guaranteeing positive secure capacity without any knowledge of Eve's location or channel.

These schemes have been experimentally validated to tolerate intense daylight, with secret capacities up to tens of Mbps at high optical noise. The protocol is implementable with present-day photon counting and time-multiplexed detectors, and directly applicable to free-space and satellite links (Mendes et al., 12 May 2025, Vazquez-Castro et al., 2024, Mendes et al., 2023, Vazquez-Castro et al., 2020). In practical LEO-to-ground implementations, keyless quantum protocols can achieve $\sim700$ Mbps secure rates at 1 GHz repetition—four to five orders of magnitude above QKD under identical constraints (Mendes et al., 2023, Vazquez-Castro et al., 2020). Table: Quantum Keyless Capacity (QKPC) vs. QKD

Protocol	Achievable Secure Rate	Security Assumptions
QKD (BB84, LEO)	$\sim$10–80 kbit/s	Eve full access, quantum attacks; symmetric
QKPC (OOK, PM)	$\sim$700 Mbit/s	Eve constrained by $\gamma\ll1$ only

Technological advances such as photon-number-resolving detection, polarization-multiplexing, and even squeezed states can further enhance keyless quantum rates and resilience to background noise (Mendes et al., 12 May 2025, Vazquez-Castro et al., 2024).

6. Semi-Quantum and Minimal Resource Protocols

"Economic Keyless Semi-Quantum Point-to-point Communication" (EKSQPC, REKSQPC) (Lu et al., 2018) demonstrates that secure direct communication does not require full quantum functionality at both endpoints. The protocols are built upon the Tele-Fetch primitive, which allows Alice to recover Bob's measurement result using a single EPR pair and Bell measurement, with no pre-shared key.

Notable features include:

• Constant quantum register size: Only one qubit needs to be stored at any time, regardless of message length.
• Constant Entanglement Preservation Time (EPT): $C+2T$, independent of session length.
• Provable information-theoretic security: Any measure-and-replay attack is detected with exponentially high probability ($1-(1-p/2)^r$ for $r$ probes, attack probability $p$), achieving detection probabilities $>0.999$ for modest parameter choices.
• Fault-tolerant operation: REKSQPC statistically distinguishes environmental noise from adversarial tampering using a Gaussian Z-test over probe results, ensuring robust performance in noisy quantum channels.

The protocols eliminate classical key management and reduce entanglement and hardware demands to the theoretical minimum for semi-quantum communication (Lu et al., 2018).

7. Trends, Applications, and Future Directions

Keyless communication achievements documented in the contemporary literature establish the feasibility of secure, scalable communication in environments where key storage, management, or distribution is costly or infeasible. Protocols exploiting information-theoretic limits, quantum noise, and device-level unpredictability now deliver confidentiality, integrity, and authentication at rates and security levels unachievable via traditional key-centric schemes in many threat models.

These paradigms are directly applicable to:

• Vehicle passive and active keyless entry, with robust relay and replay resistance.
• Internet of Things (IoT) authentication and pairing, overcoming the limitations of symmetric key storage on constrained microcontrollers.
• Space and free-space optical channels, where geometric and physical constraints provide an effective security margin unattainable by purely algorithmic cryptography.
• Mobile/wearable context-based pairing and D2D communication.

Key challenges remain in the extension to multi-user or fully decentralized environments, hardware certification for new entropy sources (memristors, nano-PUFs, squeezed-state quantum optics), and further reduction of protocol overheads. The demonstrated capacity to maintain security against unbounded adversaries in the absence of keys or with only ephemeral, physical means marks a significant and ongoing evolution in communication security architectures.