Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add OrcaQubits/agentic-commerce-skills-plugins --skill ap2-cryptographic-signinggit clone --depth 1 https://github.com/OrcaQubits/agentic-commerce-skills-pluginsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/ap2-cryptographic-signing)<a href="https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/ap2-cryptographic-signing"><img src="https://agentmods.dev/badge/skills/orcaqubits/agentic-commerce-skills-plugins/ap2-cryptographic-signing/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/ap2-cryptographic-signing"><img src="https://agentmods.dev/badge/skills/orcaqubits/agentic-commerce-skills-plugins/ap2-cryptographic-signing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00053 | $0.01308 |
| Opus 5 | $0.00026 | $0.00654 |
| Sonnet 5 | $0.00011 | $0.00262 |
| Haiku 4.5 | $0.00005 | $0.00131 |
Grade A, and why
ap2-cryptographic-signing scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 142 lines — stays where its author put it; the contents beside it link to each section on GitHub.
AP2 Cryptographic Signing
Before writing code
Fetch live docs:
- Fetch
https://ap2-protocol.org/specification/for cryptographic signing requirements - Fetch
https://ap2-protocol.org/topics/privacy-and-security/for security architecture - Web-search
site:github.com google-agentic-commerce AP2 signature mandatefor signing implementations - Web-search
ap2 protocol VDC signing cryptographic hardware-backedfor community guides
Conceptual Architecture
Why Cryptographic Signing Matters
AP2's core innovation is verifiable intent — cryptographic proof that:
- The user authorized a specific transaction
- The merchant committed to specific terms
- Neither party can deny what they agreed to (non-repudiation)
- No intermediary tampered with the mandate (integrity)
VDC Credential Format
AP2 VDCs use the SD-JWT with Key Binding (+kb) format, enabling selective disclosure and cryptographic holder binding.
Supported Signing Algorithms
AP2 supports ECDSA with the following algorithm/curve combinations:
- ES256 — ECDSA with P-256 curve
- ES384 — ECDSA with P-384 curve
- ES512 — ECDSA with P-521 curve
JSON Canonicalization (JCS)
Before signing, JSON payloads are canonicalized using JCS (RFC 8785) to produce a deterministic byte representation. This ensures that logically equivalent JSON objects produce the same signature regardless of key ordering or whitespace.
Detached JWS for Merchant Authorization
The merchant_authorization field on Cart Mandates uses Detached JWS format:
<base64url-header>..<base64url-signature>
Note the double dots — the payload is omitted from the JWS because it is the JCS-canonicalized CartContents, which the verifier already possesses.
JWT Header and Payload Requirements
JWT header MUST include:
alg— The signing algorithm (ES256, ES384, or ES512)kid— Key identifier for the signing key
JWT payload for merchant_authorization includes:
iss— Issuer (merchant identifier)aud— Audienceiat— Issued-at timestampexp— Expiration timestampjti— Unique JWT identifiercart_hash— Hash of the canonicalized cart contents
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 142 lines · 53 tokens per session scan A b5245ca1af40
ap2-cryptographic-signing is a skill published in the GitHub repository OrcaQubits/agentic-commerce-skills-plugins (39 stars, last pushed 3mo ago), licensed MIT. It adds 53 tokens to every session and 1,308 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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