> For the complete documentation index, see [llms.txt](https://hinkal-team.gitbook.io/hinkal/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hinkal-team.gitbook.io/hinkal/hinkal-waas/api-reference/sign-message.md).

# Sign Message

## Sign a message with a user's wallet

> EVM messages are plain text. Solana messages must be base64-encoded.

```json
{"openapi":"3.0.3","info":{"title":"Hinkal WaaS API","version":"1.0.0"},"tags":[{"name":"Sign Message"}],"servers":[{"url":"https://api.hinkal.io","description":"Production"}],"security":[{"XStamp":[]}],"components":{"securitySchemes":{"XStamp":{"type":"apiKey","in":"header","name":"X-Stamp","description":"Base64URL-encoded JSON: `{ \"publicKey\": \"<hex ed25519 pubkey>\", \"signature\": \"<hex ed25519 sig>\" }`.\nThe signature covers `JSON.stringify([binding, Object.entries(params)])`, where `binding`\nis `\"<METHOD> <routePath>\"` (the server's route pattern, e.g. `\"POST /waas/create-wallet\"`)\nand `params` is the request body (POST) or query params (GET). This binds the stamp to\nits own route so it cannot be replayed against a different endpoint. The one parameterized\nroute, `GET /waas/scheduled-transaction/{scheduleId}`, binds to the literal\n`\"GET /waas/scheduled-transaction/:scheduleId\"`, not the concrete ID. See the Signing\nRequests guide for runnable examples.\n"}},"schemas":{"SuccessResponse":{"type":"object","properties":{"status":{"type":"string","enum":["success"]}},"required":["status"]},"ErrorResponse":{"type":"object","properties":{"status":{"type":"string","enum":["error"]},"message":{"type":"string"}},"required":["status","message"]}},"responses":{"BadRequest":{"description":"Bad request","content":{"application/json":{"schema":{"$ref":"#/components/schemas/ErrorResponse"}}}},"Unauthorized":{"description":"Invalid or missing X-Stamp","content":{"application/json":{"schema":{"$ref":"#/components/schemas/ErrorResponse"}}}},"ServerError":{"description":"Internal server error","content":{"application/json":{"schema":{"$ref":"#/components/schemas/ErrorResponse"}}}}}},"paths":{"/waas/wallet/sign-message":{"post":{"operationId":"signMessage","summary":"Sign a message with a user's wallet","description":"EVM messages are plain text. Solana messages must be base64-encoded.","tags":["Sign Message"],"requestBody":{"required":true,"content":{"application/json":{"schema":{"type":"object","properties":{"organizationId":{"type":"string"},"userId":{"type":"string"},"fromAddress":{"type":"string"},"chainId":{"type":"string"},"message":{"type":"string","description":"Plain text for EVM; base64-encoded for Solana"},"nonce":{"type":"string"}},"required":["organizationId","userId","fromAddress","chainId","message","nonce"]}}}},"responses":{"200":{"description":"Message signed","content":{"application/json":{"schema":{"allOf":[{"$ref":"#/components/schemas/SuccessResponse"},{"type":"object","properties":{"data":{"type":"object","properties":{"signature":{"type":"string","description":"Hex-encoded signature"}}}}}]}}}},"400":{"$ref":"#/components/responses/BadRequest"},"401":{"$ref":"#/components/responses/Unauthorized"},"500":{"$ref":"#/components/responses/ServerError"}}}}}}
```