Dynamic Device Hash Derivation: Substrate Identity From Device-Local Entropy

Mechanism

Derivation of the DDH proceeds in three stages: entropy collection, epoch composition, and commitment. In the collection stage the substrate samples a vector of device-local signals. These signals are selected to satisfy two constraints simultaneously. First, each signal must exhibit sufficient within-device stability across the epoch window so that repeated derivations within a single epoch produce identical hash outputs. Second, the joint distribution of signals must contain enough entropy that an adversary lacking physical possession of the device cannot reproduce the vector from external observation alone. Representative signals include cache-line timing residuals, jitter measurements on the platform timer, voltage-rail trim values reported by the power management unit, hardware random number generator output buffered during boot, and the sequence of microarchitectural state transitions induced by a fixed challenge workload. The number and identity of signals is itself published in the substrate's enrollment record, so verifiers can audit the entropy budget without observing any individual signal value.

Signal stability is enforced by a windowing function that smooths transient excursions. Each raw sample is binned into a coarse value whose width is selected so that within-epoch variation falls inside the bin while across-device variation crosses bin boundaries. The bin widths are calibrated at enrollment by sampling each candidate signal across a representative population of devices and choosing widths that minimize the within-device variance subject to a target inter-device entropy. Because the binning is deterministic given the enrollment calibration, every fresh sample within the epoch produces the same hash, and the hash itself need not be cached: it can be regenerated on demand from current hardware state. This property is critical for systems that resist cold-boot attacks, since the entropy vector exists transiently during derivation rather than persistently in memory.

In the composition stage the entropy vector is concatenated with an epoch nonce. The nonce is not chosen by the device but is instead a deterministic function of an epoch counter that advances on a schedule defined by the platform. Because the counter advances uniformly across all participants, every device on the platform shares the same epoch boundary, and rotation of the DDH occurs synchronously across the deployed fleet. Synchronous rotation is essential to the unlinkability property: if devices rotated on independent schedules, an observer could correlate two hashes by observing that one rotated and the other did not. With fleet-wide synchronous rotation, every device's prior hash becomes invalid at the same instant, and no rotation event distinguishes one device from any other. The composition stage applies a domain-separated hash function whose first input is the epoch counter and whose second input is the entropy vector. Domain separation prevents cross-protocol confusion attacks in which an output of the DDH derivation might be replayed as an input to an unrelated protocol that uses the same hash primitive.

In the commitment stage the substrate publishes the DDH together with a zero-knowledge attestation that the value was derived by an authorized substrate within the current epoch. The attestation does not reveal the entropy vector. It commits only to the fact that some entropy vector existed which, when composed with the published epoch nonce, produced the published hash, and that the device producing the attestation holds a valid enrollment credential. Verifiers consult the platform-wide epoch schedule to confirm that the attestation is current. Stale attestations are rejected without further evaluation. The combination of synchronous rotation and zero-knowledge commitment means that the published DDH is simultaneously verifiable as a current substrate identity and unlinkable to any DDH the same substrate published in a prior epoch.

Each derivation outcome is recorded in an append-only lineage structure local to the substrate, with a digest published to the platform's distributed lineage layer. The local record retains the entropy vector under sealed storage. The published digest commits only to the hash and the epoch. This separation enables forensic reconstruction by an authorized auditor in possession of the substrate, while denying reconstruction to any party that has only the public record. The lineage commitment is what distinguishes the DDH from a self-asserted ephemeral identifier: a substrate that produces a DDH but fails to commit it cannot benefit from the rotation, because verifiers will not accept an uncommitted attestation. The commitment thus binds rotation to publication, and publication to auditability.

Operating Parameters

Three parameters govern the DDH derivation and are exposed to platform operators through a configuration channel that is itself bound to the substrate's prior-epoch DDH. The first parameter is the epoch period. Shorter periods strengthen unlinkability by reducing the window during which any single hash is valid, but increase the verification overhead by forcing more frequent attestation refreshes across the verifying population. Practical deployments select epoch periods in the range of seconds to tens of minutes depending on the trust-zone latency budget. The platform enforces a minimum epoch period to prevent denial-of-service through excessive rotation and a maximum epoch period to prevent operators from extending the window so far that the DDH effectively becomes static. Within these bounds, the choice of period is driven by the threat model: deployments concerned primarily with long-term linkage analysis select shorter periods, while deployments in which verification cost is the primary constraint select longer ones.

The second parameter is the entropy vector composition. The platform specifies a baseline set of signals that every conforming substrate must collect, and an extension set that substrates may include where supported by the underlying hardware. The baseline guarantees a minimum entropy floor; the extensions raise the floor on capable hardware. The composition is committed to in the substrate's enrollment record so that verifiers know which signals contributed to a given DDH without needing to inspect the values themselves. Verifiers can compute a lower bound on the entropy of the published hash from the enrollment record alone, and reject hashes derived from compositions whose entropy floor falls below the platform's policy minimum.

The third parameter is the attestation algorithm. The platform supports multiple attestation backends so that substrates may select an algorithm appropriate to their hardware. Substrates with hardware-rooted key storage produce attestations chained to a manufacturer endorsement; substrates without such storage produce attestations chained to a peer-witnessed enrollment. The verification protocol distinguishes the two cases and applies the trust calculus appropriate to each. Mixed populations are supported: a verifier may treat hardware-attested DDHs as eligible for higher trust tiers while still accepting peer-attested DDHs for lower-tier operations.

Beyond these three configurable parameters, the derivation enforces invariants that cannot be relaxed. The hash function is fixed at the platform layer to prevent downgrade. The epoch counter is monotonic and signed by the platform's epoch-issuance authority, preventing replay of old epochs. The lineage commitment is mandatory; a substrate that fails to publish a lineage digest within a bounded window of its DDH publication is treated as having published no DDH at all, and its prior-epoch DDH is allowed to expire without renewal. The enrollment credential is itself rotated under a schedule that strictly contains the DDH epoch schedule, so a substrate cannot retain a stale enrollment indefinitely while continuing to produce fresh DDH values.

Alternative Embodiments

Several alternative embodiments fall within the disclosed mechanism. In a first embodiment the substrate is a virtualized environment rather than a physical device. The entropy vector is collected from the hypervisor-mediated view of the underlying hardware together with virtualization-specific signals such as the page-table shadow state and the hypervisor's scheduling residuals. The DDH derived in this embodiment identifies the virtual substrate; correlating it with the underlying physical substrate requires cooperation from the hypervisor and is not possible from the published DDH alone. This embodiment is particularly relevant in cloud deployments where the physical substrate is shared among many tenants and the trust boundary lies at the virtual machine rather than at the metal.

In a second embodiment the substrate is a federation of cooperating physical devices that present a single logical execution surface. The entropy vector is composed by concatenating per-device entropy collected under a threshold scheme, and the attestation is a threshold signature over the composed vector. The federation publishes a single DDH per epoch; no individual member device's DDH is exposed. This embodiment supports deployment on tightly coupled clusters where the unit of trust is the cluster rather than any constituent node, and it tolerates the loss of any minority of cluster members without requiring a fresh enrollment of the federation.

In a third embodiment the platform operator selects a privacy-preserving derivation in which the entropy vector is processed through a verifiable random function before composition with the epoch nonce. The verifiable random function output is itself the input to the hash. This embodiment provides public verifiability that the DDH was derived correctly without disclosing any information about the underlying signals, and is appropriate for deployments in which substrates must prove conformance to derivation rules in front of mutually distrusting verifiers. The verifiable random function key is itself part of the substrate's sealed storage, so its outputs are unforgeable by any party other than the substrate.

A fourth embodiment supports forward-recovery from substrate compromise. When a substrate detects evidence of compromise, it triggers an out-of-band rotation that bypasses the regular epoch schedule. The forced rotation invalidates the current DDH immediately and produces a new DDH bound to a fresh entropy collection. Verifiers reject the prior DDH on receipt of a signed compromise notice and refresh their trust state. The signed notice is itself recorded in the substrate's lineage, so the compromise event becomes an auditable artifact rather than a silent gap.

A fifth embodiment couples the DDH derivation to a measured-boot quote. The quote, produced by the substrate's measurement subsystem at boot, is included as one signal in the entropy vector. A substrate whose boot measurements differ from the expected baseline produces a DDH that does not validate against its enrollment record, and verifiers reject the hash without revealing which measurement diverged. This embodiment binds substrate identity to substrate integrity at the firmware level, so identity rotation and integrity verification proceed under the same primitive.

Composition With Other Primitives

The DDH composes with the broader cognition-native execution platform along three interfaces. At the substrate-trust interface the DDH is the input to the trust-zone validator that decides whether a given execution surface is permitted to host a given semantic object. The validator consults the lineage layer to confirm that the substrate's DDH chain has rotated as required and applies policy rules to decide whether the current epoch's DDH is in a trusted state. Because the DDH rotates, trust decisions are bounded in time; a previously trusted substrate that ceases to publish valid DDH attestations transitions to untrusted at the next epoch boundary without explicit revocation. Revocation lists, which are a notorious operational burden in static-identity systems, are not required: the absence of a fresh attestation is itself a structural revocation.

At the routing interface the DDH is consumed by the memory-native protocol's path selection logic. Routes that traverse a substrate are scored in part by the substrate's DDH-attested trust state, and routes through substrates with stale or absent DDH attestations are deprioritized. This composition ensures that trust decisions made at the substrate layer propagate into transport-layer behavior without requiring an external policy plane. The routing layer does not need to maintain its own model of substrate trust; it consults the DDH chain at decision time and inherits whatever trust posture the platform's enrollment policy has produced.

At the lineage interface the DDH appears in the lineage records of every semantic object that executes on the substrate during the corresponding epoch. The object's lineage thus carries a forward-secure record of the substrates that hosted it, indexed by epoch. Auditors reconstructing the object's execution history can verify which trust zones it traversed without learning the persistent identity of any device, because the recorded DDH values rotate and unlink across epochs. This separation supports auditability without surveillance: an auditor can answer the question "did this object execute only on substrates that were trusted at the relevant epoch" without ever learning which physical machines those substrates were.

At the delegation interface the DDH appears in the issuance credential of every subordinate object produced by recursive delegation. A subordinate's lineage records the parent substrate's DDH at the moment of issuance, allowing post-hoc verification that the parent was a conforming substrate even though the parent's DDH has since rotated to an unlinkable successor. The delegation chain therefore carries trust evidence forward in time without persisting any identifier that an external observer could use for cross-epoch correlation.

Prior-Art Distinctions

Prior approaches to substrate identity rely on persistent hardware-rooted identifiers. Trusted Platform Module endorsement keys, Intel SGX attestation keys, and ARM TrustZone device keys all bind the substrate's identity to a single value installed at manufacture. These approaches provide strong attestation but are inherently linkable: any two operations performed by the same substrate are correlated through the shared identifier. Privacy-preserving extensions such as Direct Anonymous Attestation reduce linkability across verifiers but do not rotate the underlying identity, and they do not produce a synchronous fleet-wide rotation event that an auditor can reference. The DDH differs structurally: the published identity rotates synchronously across the fleet on a platform-defined schedule, and no persistent identifier is exposed at any layer above the sealed storage of the substrate itself.

Prior approaches to ephemeral identity, including session keys and Tor circuit identifiers, achieve unlinkability but do not provide substrate attestation. A session key proves possession of a secret but does not prove that the holder is a conforming execution substrate within a governed platform. A Tor circuit identifier identifies a relay path but says nothing about the integrity of the relays themselves. The DDH unifies these properties: it is ephemeral with respect to external observers and attestable with respect to the platform's verification protocol. The combination is not present in the prior art surveyed, and the synchronous rotation across an enrolled fleet is a further distinguishing element.

Prior approaches to fingerprint-based identity, including browser fingerprinting and TLS-stack fingerprinting, derive identity from observable behavior without device cooperation. These approaches are coarse, non-attestable, and frequently exploited for tracking against the wishes of the device operator. The DDH inverts this posture: the substrate cooperates in producing its identity, but the produced identity is bounded in time and unlinkable across boundaries. Tracking is structurally prevented rather than mitigated by policy, and the device operator has cryptographic assurance that no observer can reconstruct cross-epoch behavior from the published identity alone.

Prior approaches to rotating credentials, such as TLS session resumption tickets and OAuth refresh tokens, rotate authentication material but retain a stable subject identifier through the rotation. The subject identifier defeats the unlinkability that the rotation might otherwise provide. The DDH rotates the identifier itself rather than only the authentication material bound to it, and the platform's verification protocol does not require a stable subject identifier to evaluate trust. This distinction is structural: the DDH has no equivalent of a stable subject, and the platform is built around that absence.

Disclosure Scope

The disclosure of US 19/230,933 covers the derivation mechanism described above, including the three-stage collection, composition, and commitment process; the configurable epoch period, entropy vector composition, and attestation backend; the alternative embodiments enumerated for virtualized substrates, federated substrates, verifiable-random-function-based derivation, forced rotation under compromise, and measured-boot coupling; and the composition interfaces to the trust-zone validator, the memory-native routing layer, the lineage layer, and the delegation issuance path. The scope further covers any equivalent embodiment in which a substrate-local entropy vector is composed with a platform-issued epoch nonce to produce an attestable, rotating substrate identity that is unlinkable across epochs absent possession of the substrate's sealed storage. Implementations that omit the synchronous rotation property, that publish persistent substrate identifiers alongside the rotating value, or that derive the identity from external rather than substrate-local entropy fall outside the claimed scope. Licensees obtain the right to derive, publish, and verify DDH values within the parameters described and to compose the DDH with execution-platform primitives that consume it.