ietf-wimse-ect/draft-nennemann-wimse-ect-00.md

fullname: Christian Nennemann
organization: Independent Researcher
email: ietf@nennemann.de

normative: RFC7515: RFC7517: RFC7519: RFC7518: RFC9562: RFC9110: I-D.ietf-wimse-arch: I-D.ietf-wimse-s2s-protocol:

informative: RFC3552: RFC8693: RFC9421: I-D.ni-wimse-ai-agent-identity: SPIFFE: title: "Secure Production Identity Framework for Everyone (SPIFFE)" target: https://spiffe.io/docs/latest/spiffe-about/overview/ date: false OPENTELEMETRY: title: "OpenTelemetry Specification" target: https://opentelemetry.io/docs/specs/otel/ date: false author: - org: Cloud Native Computing Foundation I-D.ietf-scitt-architecture: RFC9449: I-D.ietf-oauth-transaction-tokens: I-D.oauth-transaction-tokens-for-agents:

--- abstract

This document defines Execution Context Tokens (ECTs), an extension to the Workload Identity in Multi System Environments (WIMSE) architecture for distributed agentic workflows. ECTs provide signed, structured records of task execution order across agent-to-agent communication. By extending WIMSE Workload Identity Tokens with execution context claims in JSON Web Token (JWT) format, this specification enables systems to maintain structured audit trails of agent execution. ECTs use a directed acyclic graph (DAG) structure to represent task dependencies and integrate with WIMSE Workload Identity Tokens (WIT) using the same signing model and cryptographic primitives. A new HTTP header field, Execution-Context, is defined for transporting ECTs alongside existing WIMSE headers.

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Introduction

Motivation

The Workload Identity in Multi System Environments (WIMSE) framework {{I-D.ietf-wimse-arch}} provides robust workload authentication through Workload Identity Tokens (WIT) and Workload Proof Tokens (WPT). The WIMSE service-to-service protocol {{I-D.ietf-wimse-s2s-protocol}} defines how workloads authenticate each other across call chains using the Workload-Identity and Workload-Proof-Token HTTP headers.

However, workload identity alone does not address execution accountability. Knowing who performed an action does not record what was done or in what order.

Regulated environments increasingly deploy autonomous agents that coordinate across organizational boundaries. Domains such as healthcare, finance, and logistics require structured, auditable records of automated decision-making and execution.

This document defines an extension to the WIMSE architecture that addresses the gap between workload identity and execution accountability. WIMSE authenticates agents; this extension records what they did and in what order.

As identified in {{I-D.ni-wimse-ai-agent-identity}}, call context in agentic workflows needs to be visible and preserved. ECTs provide a mechanism to address this requirement with cryptographic assurances.

Problem Statement

Three core gaps exist in current approaches to regulated agentic systems:

1. WIMSE authenticates agents but does not record what they actually did. A WIT proves "Agent A is authorized" but not "Agent A executed Task X, producing Output Z."

2. No standard mechanism exists to cryptographically order and link task execution across a multi-agent workflow.

3. No mechanism exists to reconstruct the complete execution history of a distributed workflow for audit purposes.

Existing observability tools such as distributed tracing {{OPENTELEMETRY}} provide visibility for debugging and monitoring but do not provide cryptographic assurances. Tracing data is not cryptographically signed, not tamper-evident, and not designed for regulatory audit scenarios.

Scope and Applicability

This document defines:

• The Execution Context Token (ECT) format ({{ect-format}})
• DAG structure for task dependency ordering ({{dag-validation}})
• Integration with the WIMSE identity framework ({{wimse-integration}})
• An HTTP header for ECT transport ({{http-header}})
• Audit ledger interface requirements ({{ledger-interface}})

The following are out of scope and are handled by WIMSE:

• Workload authentication and identity provisioning
• Key distribution and management
• Trust domain establishment and management
• Credential lifecycle management

Conventions and Definitions

{::boilerplate bcp14-tagged}

The following terms are used in this document:

Agent:

An autonomous workload, as defined by WIMSE {{I-D.ietf-wimse-arch}}, that executes tasks within a workflow.

Task:

A discrete unit of agent work that consumes inputs and produces outputs.

Directed Acyclic Graph (DAG):

A graph structure representing task dependency ordering where edges are directed and no cycles exist.

Execution Context Token (ECT):

A JSON Web Token {{RFC7519}} defined by this specification that records task execution details.

Audit Ledger:

An append-only, immutable log of all ECTs within a workflow or set of workflows, used for audit and verification.

Workload Identity Token (WIT):

A WIMSE credential proving a workload's identity within a trust domain.

Workload Proof Token (WPT):

A WIMSE proof-of-possession token used for request-level authentication.

Trust Domain:

A WIMSE concept representing an organizational boundary with a shared identity issuer, corresponding to a SPIFFE {{SPIFFE}} trust domain.

WIMSE Architecture Integration

WIMSE Foundation

The WIMSE architecture {{I-D.ietf-wimse-arch}} defines:

• Workload Identity Tokens (WIT) that prove a workload's identity within a trust domain ("I am Agent X in trust domain Y")
• Workload Proof Tokens (WPT) that prove possession of the private key associated with a WIT ("I control the key for Agent X")
• Multi-hop authentication via the service-to-service protocol {{I-D.ietf-wimse-s2s-protocol}}

The following execution accountability needs are complementary to the WIMSE scope and are not addressed by workload identity alone:

• Recording what agents actually do with their authenticated identity
• Maintaining structured execution records
• Linking actions to their predecessors with cryptographic assurance

Extension Model

ECTs extend WIMSE by adding an execution accountability layer between the identity layer and the application layer:

+--------------------------------------------------+
|  WIMSE Layer (Identity)                          |
|    WIT: "I am Agent X (spiffe://td/agent/x)"    |
|    WPT: "I prove I control the key for Agent X"  |
+--------------------------------------------------+
                       |
                       v
+--------------------------------------------------+
|  ECT Layer (Execution Accountability) [This Spec]|
|    ECT: "Task executed, dependencies met,        |
|          inputs/outputs hashed"                   |
+--------------------------------------------------+
                       |
                       v
+--------------------------------------------------+
|  Optional: Audit Ledger (Immutable Record)       |
|    "ECTs MAY be appended to an audit ledger"     |
+--------------------------------------------------+

{: #fig-layers title="WIMSE Extension Architecture Layers"}

This extension reuses the WIMSE signing model, extends JWT claims using standard JWT extensibility {{RFC7519}}, and maintains WIMSE concepts including trust domains and workload identifiers.

Integration Points

An ECT integrates with the WIMSE identity framework through the following mechanisms:

• The ECT JOSE header "kid" parameter MUST reference the public key identifier from the agent's WIT.

• In WIMSE deployments, the ECT "iss" claim SHOULD use the WIMSE workload identifier format (a SPIFFE ID {{SPIFFE}}).

• The ECT MUST be signed with the same private key associated with the agent's WIT.

• The ECT signing algorithm (JOSE header "alg" parameter) MUST match the algorithm used in the corresponding WIT.

When an agent makes an HTTP request to another agent, the Execution-Context header is carried alongside WIMSE identity headers:

HTTP Request from Agent A to Agent B:
  Workload-Identity:    <WIT for Agent A>
  Execution-Context:    <ECT recording what A did>

{: #fig-http-headers title="HTTP Header Stacking"}

When a Workload Proof Token (WPT) is available per {{I-D.ietf-wimse-s2s-protocol}}, agents SHOULD include it alongside the WIT and ECT. ECT verification does not depend on the presence of a WPT; the ECT is independently verifiable via the WIT public key.

The receiving agent (Agent B) verifies in order:

1. WIT (WIMSE layer): Verifies Agent A's identity within the trust domain. WPT verification, if present, per {{I-D.ietf-wimse-s2s-protocol}}.

2. ECT (this extension): Records what Agent A did and what precedent tasks exist.

3. Ledger (if deployed): Appends the verified ECT to the audit ledger.

Execution Context Token Format

An Execution Context Token is a JSON Web Token (JWT) {{RFC7519}} signed as a JSON Web Signature (JWS) {{RFC7515}}. ECTs MUST use JWS Compact Serialization (the base64url-encoded header.payload.signature format) so that they can be carried in a single HTTP header value.

JOSE Header

The ECT JOSE header MUST contain the following parameters:

{
  "alg": "ES256",
  "typ": "wimse-exec+jwt",
  "kid": "agent-a-key-id-123"
}

{: #fig-header title="ECT JOSE Header Example"}

alg:

REQUIRED. The digital signature algorithm used to sign the ECT. MUST match the algorithm in the corresponding WIT. Implementations MUST support ES256 {{RFC7518}}. The "alg" value MUST NOT be "none". Symmetric algorithms (e.g., HS256, HS384, HS512) MUST NOT be used, as ECTs require asymmetric signatures for non-repudiation.

typ:

REQUIRED. MUST be set to "wimse-exec+jwt" to distinguish ECTs from other JWT types, consistent with the WIMSE convention for type parameter values.

kid:

REQUIRED. The key identifier referencing the public key from the agent's WIT {{RFC7517}}. Used by verifiers to look up the correct public key for signature verification.

JWT Claims

The ECT payload contains both WIMSE-compatible standard JWT claims and execution context claims defined by this specification.

Standard JWT Claims

The following standard JWT claims {{RFC7519}} MUST be present in every ECT:

iss:

REQUIRED. StringOrURI. A URI identifying the issuer of the ECT. In WIMSE deployments, this SHOULD be the workload's SPIFFE ID in the format spiffe://<trust-domain>/<path>, matching the "sub" claim of the agent's WIT. Non-WIMSE deployments MAY use other URI schemes (e.g., HTTPS URLs or URN:UUID identifiers).

aud:

REQUIRED. StringOrURI or array of StringOrURI. The intended recipient(s) of the ECT. Because ECTs serve as both inter-agent messages and audit records, the "aud" claim SHOULD contain the identifiers of all entities that will verify the ECT. In practice this means:

• Point-to-point delivery: when an ECT is sent from one agent to a single next agent, "aud" contains that agent's workload identity. The receiving agent verifies the ECT and forwards it to the ledger on behalf of the issuer.

• Direct-to-ledger submission: when an ECT is submitted directly to the audit ledger (e.g., after a join or at workflow completion), "aud" contains the ledger's identity.

• Multi-audience: when an ECT must be verified by both the next agent and the ledger independently, "aud" MUST be an array containing both identifiers (e.g., ["spiffe://example.com/agent/next", "spiffe://example.com/system/ledger"]). Each verifier checks that its own identity appears in the array.

In multi-parent (join) scenarios where a task depends on ECTs from multiple parent agents, the joining agent creates a new ECT with the parent task IDs in "par". The "aud" of this new ECT is set according to the rules above based on where the ECT will be delivered — it is independent of the "aud" values in the parent ECTs.

iat:

REQUIRED. NumericDate. The time at which the ECT was issued. The ECT records a completed action, so the "iat" value reflects when the record was created, not when task execution began.

exp:

REQUIRED. NumericDate. The expiration time of the ECT. Implementations SHOULD set this to 5 to 15 minutes after "iat" to limit the replay window while allowing for reasonable clock skew and processing time.

The standard JWT "nbf" (Not Before) claim is not used in ECTs because ECTs record completed actions and are valid immediately upon issuance.

jti:

REQUIRED. String. A globally unique identifier for both the ECT and the task it records, in UUID format {{RFC9562}}. Since each ECT represents exactly one task, "jti" serves as both the token identifier (for replay detection) and the task identifier (for DAG parent references in "par"). Receivers MUST reject ECTs whose "jti" has already been seen within the expiration window. When "wid" is present, uniqueness is scoped to the workflow; when "wid" is absent, uniqueness MUST be enforced globally across the ECT store.

Execution Context

The following claims are defined by this specification:

wid:

OPTIONAL. String. A workflow identifier that groups related ECTs into a single workflow. When present, MUST be a UUID {{RFC9562}}.

exec_act:

REQUIRED. String. The action or task type identifier describing what the agent performed (e.g., "process_payment", "validate_safety", "calculate_dosage"). Note: this claim is intentionally named "exec_act" rather than "act" to avoid collision with the "act" (Actor) claim registered by {{RFC8693}}.

par:

REQUIRED. Array of strings. Parent task identifiers representing DAG dependencies. Each element MUST be the "jti" value of a previously verified ECT. An empty array indicates a root task with no dependencies. A workflow MAY contain multiple root tasks. Parent ECTs may have passed their own "exp" time; ECT expiration applies to the verification window of the ECT itself, not to its validity as a parent reference in the ECT store. Note: "par" is not a registered JWT claim and does not conflict with OAuth Pushed Authorization Requests (RFC 9126), which defines an endpoint, not a token claim.

Data Integrity

The following claims provide integrity verification for task inputs and outputs without revealing the data itself:

inp_hash:

OPTIONAL. String. The base64url encoding (without padding) of the SHA-256 hash of the input data, computed over the raw octets of the input. This follows the same fixed-algorithm pattern used by the DPoP "ath" claim {{RFC9449}} and the WIMSE WPT "tth" claim {{I-D.ietf-wimse-s2s-protocol}}: SHA-256 is the mandatory algorithm with no algorithm prefix in the value.

out_hash:

OPTIONAL. String. The base64url encoding (without padding) of the SHA-256 hash of the output data, using the same format as "inp_hash".

Extensions

ext:

OPTIONAL. Object. A general-purpose extension object for domain-specific claims not defined by this specification. The short name "ext" follows the JWT convention of concise claim names and is chosen over alternatives like "extensions" for compactness. Implementations that do not understand extension claims MUST ignore them.

To avoid key collisions between different domains, extension key names SHOULD use reverse domain notation (e.g., "com.example.custom_field") to avoid collisions between independently developed extensions. To prevent abuse and excessive token size, the serialized JSON representation of the "ext" object SHOULD NOT exceed 4096 bytes, and the JSON nesting depth within the "ext" object SHOULD NOT exceed 5 levels. Implementations SHOULD reject ECTs whose "ext" claim exceeds these limits.

Extension keys for domain-specific use cases MAY be defined in future documents.

Complete ECT Example

The following is a complete ECT payload example:

{
  "iss": "spiffe://example.com/agent/clinical",
  "aud": "spiffe://example.com/agent/safety",
  "iat": 1772064150,
  "exp": 1772064750,
  "jti": "550e8400-e29b-41d4-a716-446655440001",

  "wid": "a0b1c2d3-e4f5-6789-abcd-ef0123456789",
  "exec_act": "recommend_treatment",
  "par": [],

  "inp_hash": "n4bQgYhMfWWaL-qgxVrQFaO_TxsrC4Is0V1sFbDwCgg",
  "out_hash": "LCa0a2j_xo_5m0U8HTBBNBNCLXBkg7-g-YpeiGJm564",

  "ext": {
    "com.example.trace_id": "abc123"
  }
}

{: #fig-full-ect title="Complete ECT Payload Example"}

HTTP Header Transport

Execution-Context Header Field

This specification defines the Execution-Context HTTP header field {{RFC9110}} for transporting ECTs between agents.

The header field value is the ECT in JWS Compact Serialization format {{RFC7515}}. The value consists of three Base64url-encoded parts separated by period (".") characters.

An agent sending a request to another agent includes the Execution-Context header alongside the WIMSE Workload-Identity header:

GET /api/safety-check HTTP/1.1
Host: safety-agent.example.com
Workload-Identity: eyJhbGci...WIT...
Execution-Context: eyJhbGci...ECT...

{: #fig-http-example title="HTTP Request with ECT Header"}

When multiple parent tasks contribute context to a single request, multiple Execution-Context header field lines MAY be included, each carrying a separate ECT in JWS Compact Serialization format.

When a receiver processes multiple Execution-Context headers, it MUST individually verify each ECT per the procedure in {{verification}}. If any single ECT fails verification, the receiver MUST reject the entire request. The set of verified parent task IDs across all received ECTs represents the complete set of parent dependencies available for the receiving agent's subsequent ECT.

DAG Validation

Overview

ECTs form a Directed Acyclic Graph (DAG) where each task references its parent tasks via the "par" claim. This structure provides a cryptographically signed record of execution ordering, enabling auditors to reconstruct the complete workflow and verify that required predecessor tasks were recorded before dependent tasks.

DAG validation is performed against the ECT store — either an audit ledger or the set of parent ECTs received inline.

Validation Rules

When receiving and verifying an ECT, implementations MUST perform the following DAG validation steps:

1. Task ID Uniqueness: The "jti" claim MUST be unique within the applicable scope (the workflow identified by "wid", or the entire ECT store if "wid" is absent). If an ECT with the same "jti" already exists, the ECT MUST be rejected.

2. Parent Existence: Every task identifier listed in the "par" array MUST correspond to a task that is available in the ECT store (either previously recorded in the ledger or received inline as a verified parent ECT). If any parent task is not found, the ECT MUST be rejected.

3. Temporal Ordering: The "iat" value of every parent task MUST NOT be greater than the "iat" value of the current task plus a configurable clock skew tolerance (RECOMMENDED: 30 seconds). That is, for each parent: parent.iat < child.iat + clock_skew_tolerance. The tolerance accounts for clock skew between agents; it does not guarantee strict causal ordering from timestamps alone. Causal ordering is primarily enforced by the DAG structure (parent existence in the ECT store), not by timestamps. If any parent task violates this constraint, the ECT MUST be rejected.

4. Acyclicity: Following the chain of parent references MUST NOT lead back to the current ECT's "jti". If a cycle is detected, the ECT MUST be rejected.

5. Trust Domain Consistency: Parent tasks SHOULD belong to the same trust domain or to a trust domain with which a federation relationship has been established.

To prevent denial-of-service via extremely deep or wide DAGs, implementations SHOULD enforce a maximum ancestor traversal limit (RECOMMENDED: 10000 nodes). If the limit is reached before cycle detection completes, the ECT SHOULD be rejected.

Handling Unavailable Parent ECTs

In distributed deployments, a parent ECT referenced in the "par" array may not yet be available in the local ECT store at the time of validation — for example, due to replication lag in a distributed ledger or out-of-order message delivery.

Implementations MUST distinguish between two cases:

1. Parent not found and definitively absent: The parent "jti" does not exist in any accessible ECT store. The ECT MUST be rejected.

2. Parent not yet available: The parent "jti" is not present locally but may arrive due to known replication delays. Implementations MAY defer validation for a bounded period (RECOMMENDED: no more than 60 seconds).

Deferred ECTs MUST NOT be treated as verified until all parent references are resolved. If any parent reference remains unresolved after the deferral period or after the ECT's own "exp" time (whichever comes first), the ECT MUST be rejected.

Signature and Token Verification

Verification Procedure

When an agent receives an ECT, it MUST perform the following verification steps in order:

1. Parse the JWS Compact Serialization to extract the JOSE header, payload, and signature components per {{RFC7515}}.

2. Verify that the "typ" header parameter is "wimse-exec+jwt".

3. Verify that the "alg" header parameter appears in the verifier's configured allowlist of accepted signing algorithms. The allowlist MUST NOT include "none" or any symmetric algorithm (e.g., HS256, HS384, HS512). Implementations MUST include ES256 in the allowlist; additional asymmetric algorithms MAY be included per deployment policy.

4. Verify the "kid" header parameter references a known, valid public key from a WIT within the trust domain.

5. Retrieve the public key identified by "kid" and verify the JWS signature per {{RFC7515}} Section 5.2.

6. Verify that the signing key identified by "kid" has not been revoked within the trust domain. Implementations MUST check the key's revocation status using the trust domain's key lifecycle mechanism (e.g., certificate revocation list, OCSP, or SPIFFE trust bundle updates).

7. Verify the "alg" header parameter matches the algorithm in the corresponding WIT.

8. Verify the "iss" claim matches the "sub" claim of the WIT associated with the "kid" public key.

9. Verify the "aud" claim contains the verifier's own workload identity. When "aud" is an array, it is sufficient that the verifier's identity appears as one element; the presence of other audience values does not cause verification failure. When the verifier is the audit ledger, the ledger's own identity MUST appear in "aud".

10. Verify the "exp" claim indicates the ECT has not expired.

11. Verify the "iat" claim is not unreasonably far in the past (implementation-specific threshold, RECOMMENDED maximum of 15 minutes) and is not unreasonably far in the future (RECOMMENDED: no more than 30 seconds ahead of the verifier's current time, to account for clock skew).

12. Verify all required claims ("jti", "exec_act", "par") are present and well-formed.

13. Perform DAG validation per {{dag-validation}}.

14. If all checks pass and an audit ledger is deployed, the ECT SHOULD be appended to the ledger.

If any verification step fails, the ECT MUST be rejected and the failure MUST be logged for audit purposes. Error messages SHOULD NOT reveal whether specific parent task IDs exist in the ECT store, to prevent information disclosure.

When ECT verification fails during HTTP request processing, the receiving agent SHOULD respond with HTTP 403 (Forbidden) if the WIT is valid but the ECT is invalid, and HTTP 401 (Unauthorized) if the ECT signature verification fails. The response body SHOULD include a generic error indicator without revealing which specific verification step failed. The receiving agent MUST NOT process the requested action when ECT verification fails.

Audit Ledger Interface

ECTs MAY be recorded in an immutable audit ledger for compliance verification and post-hoc analysis. A ledger is RECOMMENDED for regulated environments but is not required for point-to-point operation. This specification does not mandate a specific storage technology. Implementations MAY use append-only logs, databases with cryptographic commitment schemes, distributed ledgers, or any storage mechanism that provides the required properties.

When an audit ledger is deployed, the implementation MUST provide:

1. Append-only semantics: Once an ECT is recorded, it MUST NOT be modified or deleted.

2. Ordering: The ledger MUST maintain a total ordering of ECT entries via a monotonically increasing sequence number.

3. Lookup by ECT ID: The ledger MUST support efficient retrieval of ECT entries by "jti" value.

4. Integrity verification: The ledger SHOULD provide a mechanism to verify that no entries have been tampered with (e.g., hash chains or Merkle trees).

The ledger SHOULD be maintained by an entity independent of the workflow agents to reduce the risk of collusion.

Security Considerations

This section addresses security considerations following the guidance in {{RFC3552}}.

Threat Model

The following threat actors are considered:

• Malicious agent (insider threat): An agent within the trust domain that intentionally creates false ECT claims.
• Compromised agent (external attacker): An agent whose private key has been obtained by an external attacker.
• Ledger tamperer: An entity attempting to modify or delete ledger entries after they have been recorded.
• Time manipulator: An entity attempting to manipulate timestamps to alter perceived execution ordering.

Self-Assertion Limitation

ECTs are self-asserted by the executing agent. The agent claims what it did, and this claim is signed with its private key. A compromised or malicious agent could create ECTs with false claims (e.g., claiming an action was performed when it was not).

ECTs do not independently verify that:

• The claimed execution actually occurred as described
• The input/output hashes correspond to the actual data processed
• The agent faithfully performed the stated action

The trustworthiness of ECT claims depends on the trustworthiness of the signing agent and the integrity of the broader deployment environment.

Organizational Prerequisites

ECTs operate within a broader trust framework. The guarantees provided by ECTs are only meaningful when the following organizational controls are in place:

• Key management governance: Controls over who provisions agent keys and how keys are protected.
• Ledger integrity governance: The ledger is maintained by an entity independent of the workflow agents.
• Agent deployment governance: Agents are deployed and maintained in a manner that preserves their integrity.

Signature Verification

ECTs MUST be signed with the agent's private key using JWS {{RFC7515}}. The signature algorithm MUST match the algorithm specified in the agent's WIT. Receivers MUST verify the ECT signature against the WIT public key before processing any claims. Receivers MUST verify that the signing key has not been revoked within the trust domain (see step 6 in {{verification}}).

If signature verification fails or if the signing key has been revoked, the ECT MUST be rejected entirely and the failure MUST be logged.

Implementations MUST use established JWS libraries and MUST NOT implement custom signature verification.

Replay Attack Prevention

ECTs include short expiration times (RECOMMENDED: 5-15 minutes) to limit the window for replay attacks. The "aud" claim restricts replay to unintended recipients: an ECT intended for Agent B will be rejected by Agent C. The "iat" claim enables receivers to reject ECTs that are too old, even if not yet expired.

The DAG structure provides additional replay protection: an ECT referencing parent tasks that already have a recorded child task with the same action can be flagged as a potential replay.

Implementations MUST maintain a cache of recently-seen "jti" values to detect replayed ECTs within the expiration window. An ECT with a duplicate "jti" value MUST be rejected.

Additionally, each ECT is cryptographically bound to the issuing agent via the JOSE "kid" parameter, which references the agent's WIT public key. Verifiers MUST confirm that the "kid" resolves to the "iss" agent's key (step 8 in {{verification}}), preventing one agent from replaying another agent's ECT as its own.

Man-in-the-Middle Protection

ECTs do not replace transport-layer security. ECTs MUST be transmitted over TLS or mTLS connections. When used with the WIMSE service-to-service protocol {{I-D.ietf-wimse-s2s-protocol}}, transport security is already established. HTTP Message Signatures {{RFC9421}} provide an alternative channel binding mechanism.

The defense-in-depth model provides:

• TLS/mTLS (transport layer): Prevents network-level tampering.
• WIT/WPT (WIMSE identity layer): Proves agent identity and request authorization.
• ECT (execution accountability layer): Records what the agent did.

Key Compromise

If an agent's private key is compromised, an attacker can forge ECTs that appear to originate from that agent. To mitigate this risk:

• Implementations SHOULD use short-lived keys and rotate them frequently (hours to days, not months).
• Private keys SHOULD be stored in Hardware Security Modules (HSMs) or equivalent secure key storage.
• Trust domains MUST support rapid key revocation.
• Upon suspected compromise, the trust domain MUST revoke the compromised key and issue a new WIT with a fresh key pair.

ECTs signed with a compromised key that were recorded in the ledger before revocation remain valid historical records but SHOULD be flagged in the ledger as "signed with subsequently revoked key" for audit purposes.

ECT revocation does not propagate through the DAG. If a parent ECT's signing key is later revoked, child ECTs that were verified and recorded before that revocation remain valid — they captured a legitimate execution record at the time of issuance. However, auditors reviewing a workflow SHOULD flag any ECT in the DAG whose signing key was subsequently revoked, so that the scope of a potential compromise can be assessed. New ECTs MUST NOT be created with a "par" reference to an ECT whose signing key is known to be revoked at creation time.

Collusion and False Claims

A single malicious agent cannot forge parent task references because DAG validation requires parent tasks to exist in the ledger. However, multiple colluding agents could potentially create a false execution history if they control the ledger.

Mitigations include:

• Independent ledger maintenance: The ledger SHOULD be maintained by an entity independent of the workflow agents.
• Cross-verification: Multiple independent ledger replicas can be compared for consistency.
• Out-of-band audit: External auditors periodically verify ledger contents against expected workflow patterns.

DAG Integrity Attacks

Because the DAG structure is the primary mechanism for establishing execution ordering, attackers may attempt to manipulate it:

• False parent references: A malicious agent creates an ECT that references parent tasks from an unrelated workflow, inserting itself into a legitimate execution history. DAG validation ({{dag-validation}}) mitigates this by requiring parent existence in the ECT store, and the "wid" claim scopes parent references to a single workflow when present.
• Parent omission (pruning): An agent deliberately omits one or more actual parent dependencies from the "par" array to hide that certain tasks influenced its output. Because ECTs are self-asserted ({{self-assertion-limitation}}), no mechanism can force an agent to declare all dependencies. External auditors can detect omission by comparing the declared DAG against expected workflow patterns.
• Shadow DAGs: Multiple colluding agents fabricate an entire execution history by creating a sequence of ECTs with mutual parent references. Independent ledger maintenance and cross-verification (see {{collusion-and-false-claims}} above) are the primary mitigations.

Verifiers SHOULD validate that the declared "wid" of parent ECTs matches the "wid" of the child ECT, rejecting cross-workflow parent references unless explicitly permitted by deployment policy.

Privilege Escalation via ECTs

ECTs record execution history; they do not convey authorization. Verifiers MUST NOT interpret the presence of an ECT, or a particular set of parent references in "par", as an authorization grant. The "par" claim demonstrates that predecessor tasks were recorded, not that the current agent is authorized to act on their outputs. Authorization decisions MUST remain with the identity and authorization layer (WIT, WPT, and deployment policy). As noted in {{I-D.ni-wimse-ai-agent-identity}}, AI intermediaries introduce novel escalation vectors; ECTs MUST NOT be used to circumvent authorization boundaries.

Denial of Service

ECT signature verification is computationally inexpensive (approximately 1ms per ECT on modern hardware for ES256). DAG validation complexity is O(V) where V is the number of ancestor nodes reachable from the parent references; for typical shallow DAGs this is efficient.

Implementations SHOULD apply rate limiting at the API layer to prevent excessive ECT submissions. DAG validation SHOULD be performed after signature verification to avoid wasting resources on unsigned or incorrectly signed tokens.

Timestamp Accuracy

ECTs rely on timestamps ("iat", "exp") for temporal ordering. Clock skew between agents can lead to incorrect ordering judgments. Implementations SHOULD use synchronized time sources (e.g., NTP) and SHOULD allow a configurable clock skew tolerance (RECOMMENDED: 30 seconds).

Cross-organizational deployments where agents span multiple trust domains with independent time sources MAY require a higher clock skew tolerance. Deployments using trust domain federation SHOULD document their configured clock skew tolerance value and SHOULD ensure all participating trust domains agree on a common tolerance.

The temporal ordering check in DAG validation incorporates the clock skew tolerance to account for minor clock differences between agents.

ECT Size Constraints

ECTs with many parent tasks or large extension objects can increase HTTP header size. Implementations SHOULD limit the "par" array to a maximum of 256 entries. Workflows requiring more parent references SHOULD introduce intermediate aggregation tasks. The "ext" object SHOULD NOT exceed 4096 bytes when serialized as JSON and SHOULD NOT exceed a nesting depth of 5 levels (see also {{extension-claims}}).

Privacy Considerations

Data Exposure in ECTs

ECTs necessarily reveal:

• Agent identities ("iss", "aud") for accountability purposes
• Action descriptions ("exec_act") for audit trail completeness
• Timestamps ("iat", "exp") for temporal ordering

ECTs are designed to NOT reveal:

• Actual input or output data values (replaced with cryptographic hashes via "inp_hash" and "out_hash")
• Internal computation details or intermediate steps
• Proprietary algorithms or intellectual property
• Personally identifiable information (PII)

Data Minimization

Implementations SHOULD minimize the information included in ECTs. The "exec_act" claim SHOULD use structured identifiers (e.g., "process_payment") rather than natural language descriptions. Extension keys in "ext" ({{extension-claims}}) deserve particular attention: human-readable values risk exposing sensitive operational details. See {{extension-claims}} for guidance on using structured identifiers.

Storage and Access Control

ECTs stored in audit ledgers SHOULD be access-controlled so that only authorized auditors can read them. Implementations SHOULD consider encryption at rest for ledger storage. ECTs provide structural records of execution ordering; they are not intended for public disclosure.

Full input and output data (corresponding to the hashes in ECTs) SHOULD be stored separately from the ledger with additional access controls, since auditors may need to verify hash correctness but general access to the data values is not needed.

IANA Considerations

Media Type Registration

This document requests registration of the following media type in the "Media Types" registry maintained by IANA:

Type name:

application

Subtype name:

wimse-exec+jwt

Required parameters:

none

Optional parameters:

none

Encoding considerations:

8bit; an ECT is a JWT that is a JWS using the Compact Serialization, which is a sequence of Base64url-encoded values separated by period characters.

Security considerations:

See the Security Considerations section of this document.

Interoperability considerations:

none

Published specification:

This document

Applications that use this media type:

Applications that implement agentic workflows requiring execution context tracing and audit trails.

Additional information:

Magic number(s): none File extension(s): none Macintosh file type code(s): none

Person and email address to contact for further information:

Christian Nennemann, ietf@nennemann.de

Intended usage:

COMMON

Restrictions on usage:

none

Author:

Christian Nennemann

Change controller:

IETF

HTTP Header Field Registration

This document requests registration of the following header field in the "Hypertext Transfer Protocol (HTTP) Field Name Registry" maintained by IANA:

Field name:

Execution-Context

Status:

permanent

Specification document:

This document, {{http-header}}

JWT Claims Registration

This document requests registration of the following claims in the "JSON Web Token Claims" registry maintained by IANA:

Claim Name	Claim Description	Change Controller	Reference
wid	Workflow Identifier	IETF	{{exec-claims}}
exec_act	Action/Task Type	IETF	{{exec-claims}}
par	Parent Task Identifiers	IETF	{{exec-claims}}
inp_hash	Input Data Hash	IETF	{{data-integrity-claims}}
out_hash	Output Data Hash	IETF	{{data-integrity-claims}}
ext	Extension Object	IETF	{{extension-claims}}
{: #table-claims title="JWT Claims Registrations"}

--- back

Use Cases

{:numbered="false"}

This section describes a representative use case demonstrating how ECTs provide structured execution records.

Note: task identifiers in this section are abbreviated for readability. In production, all "jti" values are required to be UUIDs per {{exec-claims}}.

Cross-Organization Financial Trading

{:numbered="false"}

In a cross-organization trading workflow, an investment bank's agents coordinate with an external credit rating agency. The agents operate in separate trust domains with a federation relationship. The DAG records that independent assessments from both organizations were completed before trade execution.

Trust Domain: bank.example
  Agent A1 (Portfolio Risk):
    jti: task-001    par: []
    iss: spiffe://bank.example/agent/risk
    exec_act: analyze_portfolio_risk

Trust Domain: ratings.example (external)
  Agent B1 (Credit Rating):
    jti: task-002    par: []
    iss: spiffe://ratings.example/agent/credit
    exec_act: assess_credit_rating

Trust Domain: bank.example
  Agent A2 (Compliance):
    jti: task-003    par: [task-001, task-002]
    iss: spiffe://bank.example/agent/compliance
    exec_act: verify_trade_compliance

  Agent A3 (Execution):
    jti: task-004    par: [task-003]
    iss: spiffe://bank.example/agent/execution
    exec_act: execute_trade

{: #fig-finance title="Cross-Organization Trading Workflow"}

The resulting DAG:

task-001 (analyze_portfolio_risk)   task-002 (assess_credit_rating)
  [bank.example]                      [ratings.example]
          \                              /
           v                            v
         task-003 (verify_trade_compliance)
           [bank.example]
                    |
                    v
         task-004 (execute_trade)
           [bank.example]

{: #fig-finance-dag title="Cross-Organization DAG"}

Task 003 has two parents from different trust domains, demonstrating cross-organizational fan-in. The compliance agent verifies both parent ECTs — one signed by a local key and one by a federated key from the rating agency's trust domain.

Related Work

{:numbered="false"}

WIMSE Workload Identity

{:numbered="false"}

The WIMSE architecture {{I-D.ietf-wimse-arch}} and service-to- service protocol {{I-D.ietf-wimse-s2s-protocol}} provide the identity foundation upon which ECTs are built. WIT/WPT answer "who is this agent?" and "does it control the claimed key?" while ECTs record "what did this agent do?" Together they form an identity-plus-accountability framework for regulated agentic systems.

OAuth 2.0 Token Exchange and the "act" Claim

{:numbered="false"}

{{RFC8693}} defines the OAuth 2.0 Token Exchange protocol and registers the "act" (Actor) claim in the JWT Claims registry. The "act" claim creates nested JSON objects representing a delegation chain: "who is acting on behalf of whom." While the nesting superficially resembles a chain, it is strictly linear (each "act" object contains at most one nested "act"), represents authorization delegation rather than task execution, and carries no task identifiers or input/output integrity data. The "act" chain cannot represent branching (fan-out) or convergence (fan-in) and therefore cannot form a DAG.

ECTs intentionally use the distinct claim name "exec_act" for the action/task type to avoid collision with the "act" claim. The two concepts are orthogonal: "act" records "who authorized whom," ECTs record "what was done, in what order."

Transaction Tokens

{:numbered="false"}

OAuth Transaction Tokens {{I-D.ietf-oauth-transaction-tokens}} propagate authorization context across workload call chains. The Txn-Token "req_wl" claim accumulates a comma-separated list of workloads that requested replacement tokens, which is the closest existing mechanism to call-chain recording.

However, "req_wl" cannot form a DAG because:

• It is linear: a comma-separated string with no branching or merging representation. When a workload fans out to multiple downstream services, each receives the same "req_wl" value and the branching is invisible.
• It is incomplete: only workloads that request a replacement token from the Transaction Token Service appear in "req_wl"; workloads that forward the token unchanged are not recorded.
• It carries no task-level granularity, no parent references, and no execution content.
• It cannot represent convergence (fan-in): when two independent paths must both complete before a dependent task proceeds, a linear "req_wl" string cannot express that relationship.

Extensions for agentic use cases ({{I-D.oauth-transaction-tokens-for-agents}}) add agent identity and constraints ("agentic_ctx") but no execution ordering or DAG structure.

ECTs and Transaction Tokens are complementary: a Txn-Token propagates authorization context ("this request is authorized for scope X on behalf of user Y"), while an ECT records execution accountability ("task T was performed, depending on tasks P1 and P2"). An agent request could carry both a Txn-Token for authorization and an ECT for execution recording. The WPT "tth" claim defined in {{I-D.ietf-wimse-s2s-protocol}} can hash-bind a WPT to a co-present Txn-Token; a similar binding mechanism for ECTs is a potential future extension.

Distributed Tracing (OpenTelemetry)

{:numbered="false"}

OpenTelemetry {{OPENTELEMETRY}} and similar distributed tracing systems provide observability for debugging and monitoring. ECTs differ in several important ways: ECTs are cryptographically signed per-task with the agent's private key; ECTs are tamper-evident through JWS signatures; ECTs enforce DAG validation rules; and ECTs are designed for regulatory audit rather than operational monitoring. OpenTelemetry data is typically controlled by the platform operator and can be modified or deleted without detection. ECTs and distributed traces are complementary: traces provide observability while ECTs provide signed execution records. ECTs may reference OpenTelemetry trace identifiers in the "ext" claim for correlation.

W3C Provenance Data Model (PROV)

{:numbered="false"}

The W3C PROV Data Model defines an Entity-Activity-Agent ontology for representing provenance information. PROV's concepts map closely to ECT structures: PROV Activities correspond to ECT tasks, PROV Agents correspond to WIMSE workloads, and PROV's "wasInformedBy" relation corresponds to ECT "par" references. However, PROV uses RDF/OWL ontologies designed for post-hoc documentation, while ECTs are runtime-embeddable JWT tokens with cryptographic signatures. ECT audit data could be exported to PROV format for interoperability with provenance-aware systems.

SCITT (Supply Chain Integrity, Transparency, and Trust)

{:numbered="false"}

The SCITT architecture {{I-D.ietf-scitt-architecture}} defines a framework for transparent and auditable supply chain records. ECTs and SCITT are complementary: the ECT "wid" claim can serve as a correlation identifier in SCITT Signed Statements, linking an ECT audit trail to a supply chain transparency record.

Acknowledgments

{:numbered="false"}

The author thanks the WIMSE working group for their foundational work on workload identity in multi-system environments. The concepts of Workload Identity Tokens and Workload Proof Tokens provide the identity foundation upon which execution context tracing is built.