---
title: "Independent witness co-signs a checkpoint (split-view resistance)"
method: POST
path: "/checkpoint/{id}/cosign"
---

# Independent witness co-signs a checkpoint (split-view resistance)

`POST /checkpoint/{id}/cosign`

## Request

- Base URL: `https://touchstone.cv`
- URL: `https://touchstone.cv/checkpoint/{id}/cosign`
- Auth: none declared

## Path parameters

- `id` integer, required

## Request body

- object
  - `witness_sub` string, required
  - `witness_pubkey` string, required
  - `witness_sig` string, required: signs touchstone-cp-witness:v1:<recorder>:<cpId>:<root>:<head>

## Response `201`

co-signed (grade verified|claimed)

## Other responses

- `409`: already co-signed

---

[API](https://skmtc.dev/touchstone/apis/touchstone-api.md) · [All operations](https://skmtc.dev/touchstone/apis/touchstone-api/llms.txt) · [OpenAPI document](https://skmtc.dev/touchstone/apis/touchstone-api/revisions/11ffeafa6a85?raw)