Cross-Modal Biological Hash Fusion

Mechanism

Cross-modal biological hash fusion applies when multiple biological signal modalities are acquired simultaneously, for example gait dynamics from accelerometer data, voice characteristics from audio capture, and cardiac rhythm from a wearable sensor. Rather than evaluate each modality against the trust-slope independently, the system produces a fused biological hash that combines continuity evidence from all acquired modalities into a single successor evaluation against the trust-slope. The fused hash encodes the individual's multi-modal biological state as a single non-invertible representation.

The defining property of the fusion is the level at which it occurs. The fusion is performed at the stable sketch level, not at the level of finished per-modality hashes and not at the level of raw biological features. Each acquired signal stream is carried through the stable sketching module to produce a per-modality stable sketch, a fusion module combines those per-modality stable sketches into a fused sketch, and the fused sketch is then processed through the biological hash generator to yield the fused hash. Because the combination happens on the noise-tolerant, non-invertible sketch representation rather than on raw features, the fused hash inherits the non-invertibility of its constituents.

Fusion at the Sketch Level

The stable sketch is the privacy-preserving middle layer of the biological identity architecture. For each acquired signal stream, the stable sketching module reduces the normalized, continuity-suitable feature stream through dimensional reduction, projection, and quantization into a vector of discrete band indices that represents the individual's biological state in a projected space. That band-index representation is the stable sketch. Fusing at this layer means the fusion module operates on per-modality band assignments, each already abstracted away from the underlying biological signal, rather than on the signals themselves.

Choosing the sketch level as the fusion point is what allows a single fused hash to stand in for the whole multi-modal observation. The biological hash generator described in the disclosure consumes a stable sketch and emits a temporally bound, domain-scoped biological hash. By presenting the generator with a fused sketch built from several modalities, the architecture obtains one biological hash that carries combined continuity evidence, so the trust-slope continuity validator performs a single successor evaluation for the moment rather than one evaluation per modality.

How Fusion Strengthens Continuity

Cross-modal fusion strengthens continuity validation because compromise of any single modality is detectable through continuity inconsistency with the other modalities. The disclosure gives voice spoofing using a recorded sample as the example: if the voice modality's stable sketch is consistent with the trust-slope but the cardiac and gait modality sketches are not, the fusion module flags the multi-modal inconsistency, and the trust-slope continuity validator applies a reduced continuity confidence that reflects the partial-modality agreement.

The converse case raises confidence rather than lowering it. If all modalities are independently consistent with the trust-slope, the fused confidence is higher than any individual modality could achieve alone, because multi-modal agreement reduces the probability of coincidental similarity. Fusion is therefore not a simple averaging of independent verdicts: it lets disagreement among modalities surface as a security signal and lets agreement among modalities compound into stronger assurance.

Policy-Configurable Fusion Weighting

The fusion weighting is configurable by policy. Different modalities may be assigned different weights based on their reliability, their spoofing resistance, and the security requirements of the current resolution context. This connects to the acquisition tiers of the architecture, where contact-based, semi-contact, and non-contact modalities produce signals of distinct quality characteristics, so a deployment can weight a high-quality contact modality more heavily than an ambient non-contact one when the context demands higher assurance.

The weighting is a configuration of the fusion, not a fixed parameter of it. The disclosure describes the weighting as policy-governed and context-dependent, and does not fix any particular weight values; the same fusion mechanism serves a high-security facility that leans on contact-based primary acquisition and a consumer device that leans on semi-contact wearable signals, with the weighting differing by deployment.

The Per-Modality Agreement Vector

In addition to the fused hash, the fusion module produces a per-modality agreement vector. This vector records which modalities contributed to the fused evaluation, what their individual continuity assessments were, and how the fusion combined them. Where the fused hash is a single opaque representation, the agreement vector is the structured account of how that representation was reached.

The per-modality agreement vector is included in the lineage record for audit and governance purposes. Because the trust-slope is itself a lineage, an ordered sequence of biological hashes linked by continuity validation, the agreement vector gives a later auditor the means to see not just that a fused successor was accepted but which modalities agreed, which dissented, and how the combination was formed. The flagged multi-modal inconsistency of a spoofing attempt is therefore preserved in the record rather than collapsed into a single pass-or-fail verdict.

Composition With the Trust-Slope

Fusion does not introduce a parallel identity mechanism; it feeds the existing one. The fused hash is an ordinary entry in the biological trust-slope, the temporal chain of biological hashes that constitutes the identity record for a biological identity within a domain. Continuity validation evaluates the fused successor against the recent trajectory exactly as it evaluates a single-modality successor, producing a graded continuity score and one of the disclosed validation outcomes, with the reduced confidence from partial-modality agreement carried into that assessment.

Because the fused hash passes through the same biological hash generator as any other entry, it carries the same temporal binding and domain separation: it is non-replayable across time and unlinkable across domains. The cumulative confidence of the trust-slope, consumed by the policy-governed authorization mechanisms, therefore reflects multi-modal agreement where fusion was used, without any change to how downstream authorization reads the chain.

Distinction From Template Matching

The fused hash is not matched against a stored template. The disclosure replaces the template-matching paradigm, in which a freshly acquired sample is compared against a stored reference template to produce a binary match-or-non-match determination, with a trust-slope paradigm in which each biological hash is evaluated for continuity with the prior sequence of hashes. Cross-modal fusion stays within that paradigm: it produces a single non-invertible fused hash that is then validated for continuity rather than matched against a template, and the verdict that emerges is a graded continuity assessment over a trajectory rather than a binary match determination.

The fusion is also continuity-aware. The strengthening and weakening of confidence both derive from whether the per-modality sketches are consistent with the trust-slope, so the same fusion step that combines modalities also exposes the cross-modal disagreement that betrays a single-modality compromise. The per-modality agreement vector then preserves that reasoning in the lineage record, recording which modalities agreed, which dissented, and how the combination was formed.

Disclosure Scope

Cross-modal biological hash fusion, comprising the production of per-modality stable sketches for simultaneously acquired biological signal modalities, the combination of those per-modality stable sketches into a fused sketch by a fusion module, the generation of a fused biological hash from the fused sketch, the strengthening of continuity validation through cross-modal agreement and the flagging of multi-modal inconsistency through partial-modality agreement, the policy-configurable fusion weighting by modality reliability and spoofing resistance, and the per-modality agreement vector recorded in the lineage record for audit and governance, is disclosed in the cognition filing (U.S. Application No. 19/647,395 and its international counterpart) at Section 9.24. This article describes that disclosed mechanism. The primitive is not limited to any particular modality combination, and applies wherever multiple simultaneously acquired biological modalities are combined into a single successor evaluation against a biological trust-slope.