Content Anchor Hash Derivation: Perceptual Identity for Non-Executing Digital Content

Mechanism

CAH derivation accepts two inputs: a capability tier identifier and an identity thread. The capability tier identifier names the level of authority an agent operates under; tiers are organized hierarchically, and each tier carries a fixed identifier that is committed to the platform's tier registry. The identity thread is a chained sequence of identity commitments that traces an agent from its instantiation to the present moment, with each commitment binding to the previous through a cryptographic link. The CAH is the output of a derivation function applied to these two inputs.

The derivation function is a hash construction whose input is the concatenation of the tier identifier, the head of the identity thread, and a domain-separation tag that distinguishes CAH derivation from other hash uses on the platform. The output is a fixed-size cryptographic value, typically 256 bits, which is the CAH proper. The derivation is purely a function of its inputs: two parties presented with the same tier and identity thread will compute the same CAH, and the CAH commits to both inputs simultaneously. Neither input can be changed without producing a different CAH, so possession of a CAH is itself evidence that the deriving party has access to the inputs from which it was derived.

Tier identifiers are immutable. Once a tier is committed to the registry, its identifier never changes; tier evolution proceeds by registering a new tier with a new identifier and recording a supersession edge from the old tier to the new. This immutability ensures that a CAH derived under a given tier remains verifiable indefinitely, even after the tier itself has been superseded in normal use.

Identity threads are append-only. An agent's identity thread begins with an instantiation commitment that binds the agent to its origination, and grows over time as the agent's state evolves. Each new commitment in the thread references the previous, forming a chain that is tamper-evident: any modification to a prior commitment invalidates every subsequent commitment, including the one used in the most recent CAH derivation. The head of the identity thread is the commitment most recently appended; the head, not the full chain, is the input to CAH derivation.

Rotation of the CAH is explicit. A new CAH is produced whenever the tier or the identity-thread head changes. Because both inputs are append-only or supersession-tracked, the rotation is deterministic: given the prior CAH and the new inputs, any party can compute the new CAH and verify that it is the legitimate successor. The supersession relation is recorded in the agent's lineage, so the chain of CAHs across an agent's lifetime is itself a tamper-evident record. Authority decisions made under an old CAH remain attributable to the old CAH; they are not retroactively migrated to the new CAH, preserving the historical record of which authority was active at the time of each decision.

The derivation is one-way. Given a CAH, recovering the tier and identity-thread inputs is computationally infeasible under standard cryptographic assumptions. This one-wayness permits a CAH to be published as an authority reference without disclosing the underlying identity thread, supporting privacy-preserving authority verification in multi-party settings. A relying party that needs to verify authority can do so only when the agent presents the corresponding inputs; without those inputs, the CAH is an opaque token that conveys no information about the underlying identity.

The domain-separation tag deserves explicit description. The platform reserves a fixed byte sequence that is prepended to every CAH derivation input and that does not appear in any other hash construction the platform performs. This separation prevents cross-protocol attacks in which an attacker could repurpose a hash output computed for one purpose as a valid CAH; without the tag, the equality of input bytes would imply equality of derived hashes, and an adversary could in principle harvest hash outputs from one subsystem and present them as authority references in another. With the tag, no hash output computed for any other purpose can collide with a CAH except by accident, the probability of which is bounded by the hash function's collision resistance.

Operating Parameters

The hash function used in CAH derivation is a parameter of the platform configuration. Constructions are disclosed using SHA-256, BLAKE3, and SHA-3, with output truncation supported for deployments where 256 bits exceeds the storage budget. The choice does not affect the structural properties of the CAH; it affects only the cryptographic strength in absolute terms and the computational cost of derivation. All participants in a platform instance share the same hash function configuration, committed in the platform genesis record.

Derivation cost is a single hash invocation over inputs whose total size is on the order of a few hundred bytes. On commodity hardware, derivation completes in tens of nanoseconds. The cost is independent of the depth of the identity thread, because the derivation consumes only the head commitment, not the full chain. Verification of a CAH against claimed inputs is a single re-derivation and a comparison, also constant-time.

Storage cost per CAH is the fixed output size, typically 32 bytes. The supersession record adds a small constant overhead per rotation, recording the old CAH, the new CAH, the rotation reason, and a timestamp committed to the platform's lineage structure. An agent that rotates rarely accumulates negligible storage overhead from its CAH chain; an agent that rotates frequently has its rotation history available for inspection without unbounded growth, because each rotation is a constant-size record.

Verification of a CAH proceeds by recomputing the derivation from the claimed tier and identity-thread head, then comparing to the presented CAH. The verification is performed by any participant in the platform without consultation with a central authority; the only inputs required are the claimed tier identifier (verifiable against the public tier registry) and the claimed identity-thread head (verifiable against the agent's published lineage). This permits authority decisions to be audited by any observer with read access to the relevant public records.

Rotation latency from the moment of an authority change to the moment a new CAH is published is bounded by the platform's lineage commit interval, typically configurable from milliseconds to seconds. Until the new CAH is committed, the prior CAH remains the active authority reference; this prevents authority gaps during rotation but also means that a rotation does not take effect retroactively. The platform may optionally enforce a brief revocation window during which the prior CAH is marked as superseded but not yet inactive, supporting graceful authority transitions.

Cross-platform recognition of a CAH requires shared configuration of the hash function, the tier registry reference scheme, and the identity-thread commitment scheme. Where these are aligned, a CAH derived on one platform is verifiable on another without translation. Where they differ, a translation step is defined that produces a derived CAH under the receiving platform's configuration, with the translation itself recorded as part of the agent's lineage so that the chain of authority remains tamper-evident across platforms.

Concurrency under CAH evaluation is well-defined. Multiple operations performed by the same agent under the same CAH may be evaluated in parallel, and each operation is independently bound to the active CAH at the moment of its commit. A rotation that occurs concurrently with in-flight operations is sequenced relative to those operations by the lineage commit order: operations whose commit precedes the rotation are bound to the prior CAH, operations whose commit follows are bound to the new CAH, and the platform exposes the active CAH for each operation through the lineage record. This precludes ambiguity about which authority covered any given operation, even under concurrent execution and rotation.

Alternative Embodiments

In a centralized cloud embodiment, the tier registry and the identity-thread commitments are maintained by a single platform operator, and CAH derivation is performed in-process by the platform substrate. Verification is performed by the same substrate, and the lineage record is committed to a local append-only log. This embodiment trades distributed trust for derivation latency in the low microseconds and is suited to single-tenant platform deployments.

In a federated multi-party embodiment, the tier registry is maintained as a shared resource across participating organizations, and identity-thread commitments are held locally to each agent's home organization. CAH derivation is performed locally to the home organization, but the resulting CAH is verifiable by any other participant by reference to the shared tier registry and the published identity-thread head. This embodiment supports cross-organizational agent interactions in which authority must be verifiable by parties outside the agent's home organization.

In a fully decentralized embodiment, the tier registry is itself a distributed structure committed to a consensus-based ledger, and identity-thread commitments are committed to the same ledger or a related one. CAH derivation is performed by the agent's host node, and verification is performed by any node with read access to the ledger. This embodiment is suited to public networks and adversarial multi-tenant environments where no single party can be entrusted with the tier registry.

In an edge embodiment, agents reside on devices with intermittent connectivity to the platform's tier registry. The tier identifier is cached locally with a freshness window, and identity-thread commitments are appended to a local thread that is reconciled with the platform on reconnection. CAH derivation proceeds against the local cache; on reconnection, any rotations missed during disconnection are applied to produce a current CAH, and the lineage record captures both the disconnected operation and the reconciliation event.

In a key-rotated embodiment, the identity-thread commitment scheme uses a rotating key material whose rotations are themselves recorded as identity-thread events. A key rotation produces a new identity-thread head and therefore a new CAH, with the supersession relation recorded as in any other rotation. This embodiment supports cryptographic hygiene policies that require regular key rotation without disrupting the structural authority chain.

In a multi-tier embodiment, an agent operates simultaneously under multiple tiers, with one CAH derived per tier. The agent's authority for a given operation is determined by selecting the appropriate CAH from the agent's CAH set; the selection is deterministic and recorded in the lineage. This embodiment supports agents that act in multiple authority contexts, such as a service agent that has both a tenant-scoped tier and a platform-scoped tier.

In a delegated embodiment, an agent may delegate a subset of its authority to a child agent by deriving a child CAH from the parent's CAH and a delegation tier identifier. The delegation is recorded in both agents' lineages, and the child CAH is verifiable by recomputing the derivation from the parent CAH and the delegation tier. Revocation of delegation is performed by rotating the parent CAH, which invalidates the derivation chain to any unrevoked children.

In a hardware-bound embodiment, the identity thread incorporates an attestation drawn from a hardware security module or trusted execution environment, and the head of the identity thread carries a binding to the attesting hardware. CAH derivation in this embodiment is unchanged in form, but the identity-thread input now carries hardware-rooted assurance, and a verifier can chain its trust in the CAH back to the hardware attestation through the lineage. This embodiment is appropriate for high-assurance deployments where the binding between an executing agent and a specific hardware platform must be cryptographically demonstrated.

Composition

CAH derivation composes with the broader cognition-native execution platform along three axes. Along the lineage axis, the CAH and its rotations are recorded in the same append-only structure that records all other state transitions of the agent. The chain of CAHs across the agent's lifetime is therefore a connected substructure of the agent's lineage, and any tooling that consumes the lineage can reconstruct the authority history without special-case handling.

Along the governance axis, the CAH is the authority reference consulted by the platform's governance evaluation step. Every operation that the agent attempts is checked against the active CAH and the governance class associated with the targeted resource. The check is constant-time, and its outcome is recorded as part of the lineage so that the authority decision is itself tamper-evident. Rotation of the CAH does not retroactively alter past authority decisions; each decision is bound to the CAH that was active at the time of the decision.

Along the substrate axis, CAH derivation is independent of the underlying compute and storage technology. The same derivation produces the same CAH regardless of whether the substrate is in-process, federated, decentralized, or edge, and verification is identical in all cases. This substrate-independence is what permits agents to migrate across substrates while retaining their authority chain, and what permits cross-substrate authority verification without a translation step where the platform configurations align.

Composition with the trust zone mechanism of the execution platform is particularly tight. A trust zone is a region of the substrate within which a defined set of CAHs is recognized as bearing authority. An agent entering a trust zone presents its CAH; the trust zone verifies the CAH against the zone's recognized tier set and the agent's identity thread, and admits or rejects accordingly. The trust zone does not need to consult a central authority; verification is local and constant-time.

Composition with the semantic agent interaction protocol permits agents to authenticate to one another through CAH exchange. An agent presents its CAH along with a challenge response derived from the identity-thread head; the receiving agent verifies the derivation and the response, establishing both the presenting agent's authority and its possession of the corresponding identity thread. This authentication is performed without any third-party authority, and the resulting interaction record is committed to both agents' lineages.

Prior-Art Distinction

Conventional capability systems address the authority problem through capability tokens, role-based access control records, and centralized identity providers. Capability tokens are unforgeable references to authority that are passed between parties; their unforgeability typically depends on a signing key held by an issuer, and revocation requires consulting the issuer or a revocation list. Role-based access control assigns roles to identities and permissions to roles, evaluated against a central policy decision point. Centralized identity providers issue identity assertions consumed by relying parties, with the assertions valid only as long as the provider remains available and honest.

CAH derivation removes these dependencies by constructing the authority reference deterministically from the tier and the identity thread, both of which are public structures committed to the platform's lineage. There is no issuer whose signing key must be guarded; the CAH is not signed but derived. There is no central policy decision point; verification is local. There is no identity provider whose availability is required at decision time; the identity thread is part of the agent's own state. Revocation is performed by tier or identity-thread rotation, with the supersession relation tamper-evidently recorded.

Cryptographic hash chains and Merkle audit logs provide a partial analog at the data-integrity layer but do not specify the dual-input derivation that binds a tier to an identity thread, nor the rotation semantics that make the supersession relation explicit. The CAH construction here combines hash-chain integrity with explicit dual-input binding and rotation tracking, none of which the prior systems combine in this configuration.

Decentralized identifier (DID) systems provide a public identity layer with rotation support but do not specify the tier binding that converts identity into authority within a defined governance regime. A DID identifies a subject; a CAH identifies a subject acting under a specified authority tier. The two layers are complementary, and a CAH construction may use a DID-style identifier as its identity-thread input, but the CAH itself is a distinct primitive at the authority layer.

Hardware-attested identity systems such as TPM-based attestation provide a strong binding between an identity and a hardware root of trust but typically do not provide a substrate-independent authority reference suitable for cross-platform recognition. CAH derivation is hardware-neutral and platform-portable in a way that hardware attestation is not.

The combination of dual-input derivation from tier and identity thread, append-only identity-thread input, immutable tier identifier, explicit rotation with supersession recording, one-way derivation, and substrate-independent verification distinguishes the CAH construction from each of the cited references.

Disclosure Scope

This article describes CAH derivation at a level sufficient to enable a person of ordinary skill in cryptographic capability systems to implement it. The disclosure encompasses the dual-input derivation function, the immutable tier identifier and its registry, the append-only identity thread and its head input, the explicit rotation semantics with supersession recording, the one-way derivation property, the constant-time verification, and the substrate-independent operating parameters. Embodiments are disclosed across centralized, federated, decentralized, edge, key-rotated, multi-tier, and delegated configurations.

The disclosure is non-limiting with respect to the choice of hash function, the specific tier registry implementation, the identity-thread commitment scheme, and the storage backend for lineage records. Variations in any of these implementation details are within the scope of the disclosure provided that the structural properties of dual-input derivation, append-only identity input, explicit rotation, and substrate-independent verification are retained.

This article is part of a series describing the cognition-native execution platform for distributed stateful and governable agents. Related disclosures cover the trust zone mechanism, the semantic agent interaction protocol, and the governance evaluation step; together they constitute the full architectural specification for the platform's authority and governance layers.