sign_challenge · Tether Name MCP: Risk & Policy

WHAT IT DOES

What sign_challenge does on Tether Name

AI agents invoke sign_challenge to trigger actions in Tether Name. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why sign_challenge needs a policy

This tool performs a cryptographic signing operation using a private key. It executes an external cryptographic operation that produces a signature used for authentication/verification. It doesn't merely read data, but actively performs a computation with security implications — signing with a private key could be misused to authenticate as an agent or approve actions on behalf of an identity.

From the tool's definition Sign a challenge string using the configured RSA private key. Returns a URL-safe base64 encoded signature.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

sign_challenge Rate-limited

sign_challenge stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "sign_challenge": {
      "limits": [
        {
          "counter": "sign_challenge_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Tether Name, so you can run agents against it safely.

FAQ

Questions about sign_challenge

What does the sign_challenge tool do? +

Sign a challenge string using the configured RSA private key. Returns a URL-safe base64 encoded signature. It is categorised as a Execute tool in the Tether Name MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on sign_challenge? +

Register the Tether Name MCP server in PolicyLayer and add a rule for sign_challenge: 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 Tether Name. Nothing to install.

What risk level is sign_challenge? +

sign_challenge is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit sign_challenge? +

Yes. Add a rate_limit block to the sign_challenge 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.

How do I block sign_challenge completely? +

Set action: deny in the PolicyLayer policy for sign_challenge. 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.

What MCP server provides sign_challenge? +

sign_challenge is provided by the Tether Name MCP server (tether-name-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.