Entity-Specific Cryptographic Identity: Non-Transferable Key Derivation from Temporal Data

The emergence of Soulbound Tokens (SBTs) highlights growing demand for non-transferable digital identity primitives in decentralized systems. Current approaches to SBT implementation rely on social recovery mechanisms or trusted issuers, both of which introduce transferability vectors through key delegation. This paper presents Entity-Specific Key Derivation (ESKD), a theoretical framework for deriving cryptographic keys from entity-unique temporal data—specifically birth timestamps and associated astronomical configurations. We prove that keys derived through ESKD achieve mathematical non-transferability: the derivation process cannot be delegated to non-entities without producing detectable anomalies. Our framework satisfies four critical properties: uniqueness, non-transferability, verifiability, and lifetime validity. Building upon the Configuration Space Cryptography framework and Natural Key Distribution taxonomy established in companion papers, we demonstrate how ESKD can serve as a foundational primitive for SBT ecosystems, enabling credential verification, reputation portability, and identity-bound authentication without trusted third parties. Part of the Configuration Space Cryptography research series. Related works: Natural Key Distribution (DOI: 10.5281/zenodo.18013432), Configuration Space Cryptography (DOI: 10.5281/zenodo.18013666), Adversary Models (DOI: 10.5281/zenodo.18014097), MDSA (DOI: 10.5281/zenodo.18014295).