sign_message_btc
Sign a UTF-8 message with a paired Bitcoin address using the Bitcoin Signed Message format (BIP-137). Returns a base64-encoded compact signature with a header byte that matches the address-type convention (legacy / P2SH-wrapped / native segwit) AND messageSha256 — a lowercase hex SHA-256 of the e...
This record as markdown: /tools/io-github-szhygulin-vaultpilot-mcp/sign-message-btc.md
What sign_message_btc does on VaultPilot MCP
AI agents invoke sign_message_btc to trigger actions in VaultPilot MCP. 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.
| Parameter | Type | Required | Description |
|---|---|---|---|
wallet | string | Yes | Paired Bitcoin source address. Must already be in `pairings.bitcoin` (call `pair_ledger_btc` first). Phase 1 message-signing supports legacy (`1...`), P2SH-wrap |
message | string | Yes | UTF-8 message to sign. Typical Sign-In-with-Bitcoin payloads are a few hundred chars; capped at 10000 because the Ledger BTC app's on-device review window chunk |
Parameters from the server's own tool schema.
Why sign_message_btc is rated High
This tool triggers an external cryptographic signing operation on a hardware device (Ledger Nano), producing a cryptographic signature tied to a Bitcoin address. While it does not move funds directly, signing messages with private keys is a privileged operation — misuse could facilitate phishing, authorization of off-chain agreements, or enable replay-style attacks.
From the tool's definition Sign a UTF-8 message with a paired Bitcoin address using the Bitcoin Signed Message format (BIP-137). Returns a base64-encoded compact signature... Surface messageSha256 in the verbatim message-sign block
Attacks that exploit this kind of access
The rule that runs sign_message_btc safely
PolicyLayer is an MCP gateway: it sits between your AI agents and VaultPilot MCP, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For sign_message_btc, this is the rule to start with:
sign_message_btc 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.
The button opens the PolicyLayer dashboard: create your workspace, connect VaultPilot MCP, apply this rule, and every sign_message_btc call is checked against it from then on.
Questions about sign_message_btc
Sign a UTF-8 message with a paired Bitcoin address using the Bitcoin Signed Message format (BIP-137). Returns a base64-encoded compact signature with a header byte that matches the address-type convention (legacy / P2SH-wrapped / native segwit) AND messageSha256 — a lowercase hex SHA-256 of the exact UTF-8 bytes submitted to the device (Inv #8 byte-fingerprint, issue #454). Surface messageSha256 in the verbatim message-sign block so the user can recompute on a separate device (printf '%s' '<message>' | sha256sum) and catch unicode-confusable substitution attacks the Ledger Nano OLED can't show in full. The Ledger BTC app prompts the user to confirm the message text on-device before signing — same clear-sign UX as send-side flows. DRAINER-STRING REFUSAL (issue #454): the MCP refuses messages containing value-transfer / authorization markers (transfer / authorize / grant / custody / release / consent) or explicit drainer templates ("I authorize", "granting full custody", "I consent to", "I hereby transfer", "release my") BEFORE any device interaction — fires regardless of agent cooperation. Legitimate Sign-In-with-Bitcoin / proof-of-funds flows don't use these markers. Taproot (bc1p…) addresses are refused: BIP-322 (taproot's canonical message scheme) is not yet exposed by the Ledger BTC app; sign with one of your other paired address types from the same Ledger account instead. It is categorised as a Execute tool in the VaultPilot MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
sign_message_btc accepts 2 parameters: wallet, message. Required: wallet, message. The full parameter table on this page comes from the server's own tool schema.
Register the VaultPilot MCP server in PolicyLayer and add a rule for sign_message_btc: 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 VaultPilot MCP. Nothing to install.
sign_message_btc is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the sign_message_btc 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 sign_message_btc. 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.
sign_message_btc is provided by the VaultPilot MCP server (vaultpilot-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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