# Relay: Get Message Hash

Fetch the message-hash that the signing ceremony was opened against — used by a joining party to verify it is signing what it expects.

## Overview

When a session is opened with `/sign/start`, the requested `msgHashHex` is recorded server-side. The DEVICE (or BACKUP) party fetches it here before contributing its share, so it can double-check the hash matches the locally computed hash of the transaction being signed — defense-in-depth against a tampered client.

### `GET /v1/mpc/relay/session/{id}/msghash`

Authentication: bearer token required.

Returns the msgHashHex captured at /sign/start.

**Path parameters**

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `id` | string | yes | Relay session id |

**Responses**

`200` OK

```json
{ "msgHashHex": "9a3b…f0" }
```

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Web version: https://docs.aureahub.com/#mpc-relay-msghash