Additional Use Cases for Automatic Certificate Management (ACME)
draft-mattsson-acme-use-cases-00

Abstract

Contacting a CA is just one way in which a newly deployed HTTPS server can get hold of the certificate to use. This document describes additional (and common) use cases that fall into the major guiding use case for ACME as stated by [I-D.barnes-acme], “obtaining certificates for Web sites”.

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Table of Contents

• 1. Introduction
• 2. Additional Use Cases
• 3. References
• Authors' Addresses

1. Introduction

It is well known that security features should be on by default and automatically configured. Otherwise the risk is overwhelming that the security features are left unused, or used in non-secure ways. One important task that benefits from more automation is certificate management.

The document [I-D.barnes-acme] describes the use case where an HTTPS web server contacts a certification authority (CA) to request (and often pay for) a new domain validation certificate for a domain. But contacting a CA is just one way in which a newly deployed HTTPS server can get hold of the certificate to use.

This document describes additional (and common) use cases that fall into the major guiding use case for ACME as stated by [I-D.barnes-acme], “obtaining certificates for Web sites”. To fulfill the needs of these use cases, we introduce the following certificate management function for ACME:

• Certificate Download

where the ACME server is not the CA, but rather a server operated by the domain owner.

Just as the main scenario in [I-D.barnes-acme], the scenarios in this document often uses a collection of ad hoc mechanisms. And while [I-D.barnes-acme] mentions the already horrible 1-3 hours to obtain and install certificates for a newly deployed HTTPS server, the process of transferring an existing certificate can be even more time consuming, and people flying back on forth just to manually transfer certificates is not unheard of.

2. Additional Use Cases

A newly deployed HTTPS server replacing or complementing an existing HTTPS server should import an existing certificate instead of buying a new. In the flow diagram in Figure 1, the new HTTPS server (ACME CLIENT) requests, downloads, and imports an existing certificate from a server (ACME SERVER). A PKCS#10 Certificate Signing Request (CSR) cannot be used as that creates a new certificate. Instead the client sends a request (here called CertDownload) to request download of an existing certificate. Authorization may e.g. be based on authentication of the computer operator.

ACME CLIENT                   ACME SERVER


Identifier      ------->

                <-------      Challenges

Responses       ------->

                <-------      Authorization

CertDownload    ------->

                <-------      Certificate

HTTPS SERVER                  REPOSITORY                              CA


                              Identifier       ------->

                                               <-------       Challenges

                              Responses        ------->

                                               <-------    Authorization

                              CSR              ------->

                                               <-------      Certificate
Identifier      ------->

                <-------      Challenges

Responses       ------->

                <-------      Authorization

CertDownload    ------->

                <-------      Certificate     

HTTPS SERVER                  DOMAIN OWNER                            CA


Identifier      ------->
                              Identifier       ------->

                                               <-------       Challenges
                <-------      Challenges


Responses       ------->
                              Responses        ------->

                                               <-------    Authorization
                <-------      Authorization


CSR             ------->
                              CSR              ------->

                                               <-------      Certificate
                <-------      Certificate