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...
AI agents call sign_message_btc to permanently remove resources in VaultPilot MCP — typically in cleanup and lifecycle workflows. It does its job in a single call, and there is no undo.
| 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.
An AI agent that decides to call sign_message_btc doesn't hesitate, doesn't double-check, and doesn't stop at one. Whatever it removes from VaultPilot MCP is gone — there is no undo for destructive operations.
Attacks that exploit this kind of access
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 Destructive tool in the VaultPilot MCP MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.
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 Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.
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.