> For the complete documentation index, see [llms.txt](https://docs.emudhradigital.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.emudhradigital.com/documentation/remote-signing-document-signer/architecture.md).

# Architecture

```
  Customer systems (core banking, ERP, HRMS, LMS, batch jobs)
        │  REST API (mTLS / API key, IP allow-list)
        ▼
 ┌──────────────────── eMudhra Remote Signing Service ───────────────────┐
 │  API gateway → Signing policy engine → Template & appearance service │
 │                     │                                                │
 │                     ▼                                                │
 │       Signer key vault (HSM, FIPS 140-3 L3)  ◄── Key ceremony / CA   │
 │                     │                                                │
 │       TSA (RFC 3161) · OCSP/CRL embedding (LTV) · Audit log          │
 └──────────────────────────────────────────────────────────────────────┘
        │
        ▼  signed PDF / CMS / XML returned to customer
```

| Component                         | Role                                                                                         |
| --------------------------------- | -------------------------------------------------------------------------------------------- |
| **API gateway**                   | Authenticates client applications (API credentials, mTLS, IP allow-listing) and rate-limits. |
| **Signing policy engine**         | Maps each client/application to permitted signer certificates, document types and limits.    |
| **Template & appearance service** | Places visible signatures (position, page, image, reason, location) on PDFs.                 |
| **HSM key vault**                 | Holds Document Signer private keys; signing operations occur inside the HSM.                 |
| **TSA / LTV**                     | Adds trusted timestamps and embeds revocation data for long-term validation.                 |
| **Audit log**                     | Records every signing request: client, certificate, document hash, timestamp, outcome.       |

## Deployment options

| Option                        | Description                                                                                              |
| ----------------------------- | -------------------------------------------------------------------------------------------------------- |
| **eMudhra cloud**             | Fully hosted service in eMudhra's India data centres.                                                    |
| **Private cloud / dedicated** | Dedicated instance and HSM partition for a single customer.                                              |
| **On-premises**               | Signing server deployed in the customer's DC with the customer's HSM; certificates issued by eMudhra CA. |