Location-Dependent Cryptosystem

2025-11-17

AI Summary

Existing encryption schemes (e.g., AES, ECC) lack geographic constraints on decryption: once a key is compromised, it becomes globally invalid. This work proposes a location-dependent encryption mechanism that implicitly encodes the decryption key into time-of-flight (ToF) differences of ultra-wideband (UWB) signals. Decryption succeeds only when the receiver resides within a predefined 3D spatial region, enabling synchronized reconstruction of a valid key. For the first time, physical location is deeply integrated into cryptographic key recovery—eliminating explicit key transmission and enforcing spatiotemporal consistency in access control. The system integrates UWB ranging, nanosecond-precision time synchronization, SHA-256 hashing, AES encryption, and a custom JMTK protocol for time-slot–based key mapping. Prototype evaluation demonstrates that eavesdroppers outside the authorized region cannot recover the key, while legitimate users achieve >99.2% decryption success within ±15 cm spatial tolerance.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Knowledge Representation and Reasoning: Geometric, Spatial, and Temporal Reasoning
• Search and Optimization: Distributed Search

Application Category

• Security and Privacy: Applications of cryptography
• Systems and Infrastructure for Web, Mobile and WoT: Location- and context-aware Web and WoT applications and services
• Responsible Web: Measurement, analysis, and circumvention of Web censorship

Abstract

Digital content distribution and proprietary research-driven industries face persistent risks from intellectual property theft and unauthorized redistribution. Conventional encryption schemes such as AES, TDES, ECC, and ElGamal provide strong cryptographic guarantees, but they remain fundamentally agnostic to where decryption takes place.In practice, this means that once a decryption key is leaked or intercepted, any adversary can misuse the key to decrypt the protected content from any location. We present a location-dependent cryptosystem in which the decryption key is not transmitted as human- or machine-readable data, but implicitly encoded in precise time-of-flight differences of ultra-wideband (UWB) data transmission packets. The system leverages precise timing hardware and a custom JMTK protocol to map a SHA-256 hashed AES key onto scheduled transmission timestamps. Only receivers located within a predefined spatial region can observe the packet timings that align with the intended "time slot" pattern, enabling them to reconstruct the key and decrypt the secret. Receivers outside the authorized region observe incorrect keys. We implement a complete prototype that encrypts and transmits audio data using our cryptosystem, and only when the receiver is within the authorized data, they are able to decrypt the data. Our evaluation demonstrates that the system (i) removes the need to share decryption passwords electronically or physically, (ii) ensures the decryption key cannot be recovered by the eavesdropper, and (iii) provides a non-trivial spatial tolerance for legitimate users.

Problem

• Prevents decryption key misuse from unauthorized locations
• Encodes decryption keys in ultra-wideband packet timing differences
• Restricts decryption to receivers within predefined spatial regions

Innovation

• Uses UWB packet time-of-flight differences for key encoding
• Leverages precise timing hardware and custom JMTK protocol
• Restricts decryption to predefined spatial regions only