hmac_sign_verify
utilpeek: Returns the HMAC of a message under a shared key (sign), or whether a signature matches it in constant time (verify); handles GitHub (sha256= prefix accepted), Stripe v1 (of {t}.{raw body}) and Slack v0 (of v0:{timestamp}:{raw body}) webhook signatures. For plain digests use hash_text; ...
This record as markdown: /tools/dev-tanod-tanod/hmac-sign-verify.md
What hmac_sign_verify does on Tanod
AI agents call hmac_sign_verify to retrieve information from Tanod without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
| Parameter | Type | Required | Description |
|---|---|---|---|
key | string | Yes | The shared secret (at most 1 KiB), read as `key_encoding`. Never echoed or logged. |
mode | string | Yes | sign (compute the HMAC) or verify (check `signature`). |
output | string | — | Signature encoding: hex (default) or base64. |
message | string | Yes | The signed payload exactly as received (e.g. the raw webhook body), as text; at most 64 KiB as UTF-8. |
algorithm | string | — | sha256 (default), sha512, or sha1 (legacy webhooks only). |
signature | object | — | verify only: the signature to check, in `output` encoding. A `sha256=` style prefix (GitHub's X-Hub-Signature-256) is stripped when it names `algorithm`. |
key_encoding | string | — | utf8 (default), hex or base64 (standard alphabet). |
Parameters from the server's own tool schema.
Why hmac_sign_verify is rated Low
Even though hmac_sign_verify only reads data, uncontrolled read access leaks sensitive information and racks up API costs: an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.
Attacks that exploit this kind of access
The rule that runs hmac_sign_verify safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Tanod, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For hmac_sign_verify, this is the rule to start with:
hmac_sign_verify is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Tanod, apply this rule, and every hmac_sign_verify call is checked against it from then on.
Questions about hmac_sign_verify
utilpeek: Returns the HMAC of a message under a shared key (sign), or whether a signature matches it in constant time (verify); handles GitHub (sha256= prefix accepted), Stripe v1 (of {t}.{raw body}) and Slack v0 (of v0:{timestamp}:{raw body}) webhook signatures. For plain digests use hash_text; for JWTs use verify_jwt. Input: mode, message, key, optional key_encoding, algorithm, output and, for verify, signature. Malformed hex or base64, a sha*= prefix naming another algorithm, or verify without a signature is a 422 (not charged). Other prefixes (v0=, v1=) are not stripped. sha1 is for legacy webhooks only. The key and message are never echoed. Typically under 0.1 s. Price: USD 0.001. Free: 10 utilpeek calls per IP per UTC day. The submitted text is never logged or stored. Docs: https://tanod.dev/learn/verify-webhook-signature-hmac-api.html. It is categorised as a Read tool in the Tanod MCP Server, which means it retrieves data without modifying state.
hmac_sign_verify accepts 7 parameters: key, mode, output, message, algorithm, signature, key_encoding. Required: key, mode, message. The full parameter table on this page comes from the server's own tool schema.
Register the Tanod MCP server in PolicyLayer and add a rule for hmac_sign_verify: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Tanod. Nothing to install.
hmac_sign_verify is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the hmac_sign_verify rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for hmac_sign_verify. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
hmac_sign_verify is provided by the Tanod MCP server (https://tanod.dev/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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