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Blog Security What Is Automatic Certificate Management Environment (ACME) Protocol and How Does It Work?


July 26 2023


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What Is ACME Protocol and How Does It Work?

The Automated Certificate Management Environment ACME protocol has revolutionized the way certificates are managed in today’s digital landscape. With its standardized and automated approach, ACME simplifies the process of obtaining, renewing, and revoking certificates. By streamlining certificate management, ACME enhances security, reduces administrative burden, and ensures the seamless operation of secure web services.

What Is ACME?

On average, an administrator can spend from one to three hours setting up an SSL certificate for a domain. If you make a mistake, you will have to wait until the application is rejected, only after that it can be submitted again. All this makes it difficult to deploy large-scale systems.

The domain validation process may differ for each certification authority. Lack of standardization sometimes leads to security problems. There is a known case when, due to a bug in the system, one CA verified all declared domains. In such situations, SSL certificates can be issued to fraudulent resources.

The ACME protocol was designed by the Internet Security Research Group (ISRG) for its own certificate service public CA. The IETF-approved ACME protocol (RFC8555 specification) is supposed to automate and standardize the process of obtaining a certificate. And eliminating the human factor will help increase the reliability and security of domain name verification.

The standard is open and anyone can contribute to its development. The GitHub repository has instructions for this.

ACME Versions

ACME v1 introduced a standardized framework for issuing and managing digital certificates, revolutionizing the way web servers and services interacted with certificate authorities. ACME v1 provided essential features such as domain validation, certificate signing requests (CSRs), and automated certificate renewal.

ACME v2 addressed various limitations and introduced notable enhancements. One of the key additions in ACME v2 was the support for wildcard certificates, allowing organizations to secure multiple subdomains with a single certificate. Moreover, v2 brought improved error handling, expanded authorization methods, and introduced more flexible key management options.

How Does the Protocol Work?

Requests in ACME are exchanged over HTTPS using JSON messages. To work with the protocol, you need to install an ACME client on the target node; it generates a unique authorized key pair the first time it accesses the CA. Subsequently, they will be used to sign all client and server messages.

The first message contains client contacts information. It is signed with the corresponding private key and sent to the ACME server along with the public key. It checks the authenticity of the signature and, if everything is in order, starts the procedure for issuing an SSL certificate.

To obtain a certificate, the client must prove to the server that it owns the domain. To do this, he performs certain actions that are available only to the owner. For example, a certificate authority can generate a unique token and ask the client to place it on the site. Next, the CA issues a web or DNS query to extract the key from this token.

For example, in the case of HTTP, the key from the token must be placed in a file that will be served by the web server. During DNS verification, the certification authority will look for a unique key in the text document of the DNS record. If everything is in order, the server confirms that the client has been validated and the CA issues a certificate.

How Does ACME Support Certificate Lifecycle Management?

Automated Certificate Management Environment ACME offers a standardized and automated approach to certificate issuance, renewal, revocation, and management. The ACME protocol functions by installing a certificate management agent on a web server.

ACME agent facilitates the initial certificate issuance by providing a seamless process for domain validation. It offers various validation methods, such as HTTP-based challenges or DNS-based challenges, ensuring the entity requesting the certificate has control over the domain in question.

Instead of manual intervention, ACME enables automated certificate renewal by allowing servers to request new certificates before the existing ones expire. This ensures that certificates remain valid without disruption, reducing the risk of expired certificates.

ACME supports certificate revocation. In case a certificate needs to be revoked before its expiration, ACME provides an efficient mechanism for revocation requests. This helps mitigate risks associated with compromised or outdated certificates.

Furthermore, ACME aids in certificate management by offering standardized interfaces for key generation, key rotation, and certificate storage. It allows for easy integration with certificate management systems and provides a consistent and reliable approach to managing certificates at scale.

What Types of TLS/SSL Certificates and Other PKI Certificates Does it Support?

ACME major part of TLS/SSL certificates and other PKI certificates commonly used. It accommodates various certificate types to meet different security and authentication needs:

Domain Validated DV Certificates: verify domain ownership and are ideal for basic encryption and securing websites.

Organization Validated OV Certificates: validate domain ownership as well as the legal existence of the organization behind the domain.

Extended Validation EV Certificates: provide the highest level of trust and authentication. EV certificates require rigorous validation of the organization’s identity and offer visual indicators like the green address bar.

Wildcard Certificates: secure a domain and all its subdomains, providing flexibility and ease of management.

Code Signing Certificates: used to digitally sign software, ensuring its authenticity and integrity.

Client Certificates: enabling secure client authentication for accessing resources or services.

Setting up ACME

ACME is a script written in the Shell (Unix) language, with no dependencies on Python or the official Let’s Encrypt client. It does not require root or sudoer access.

Acme can be installed on major Linux distributions such as Ubuntu, CentOS, Debian, Archlinux, OpenSUSE, Fedora, and many more.

We can install ACME with git by cloning the official project:

From the terminal, issue this command:

git clone https://github.com/Neilpang/acme.sh.git

Enter the new folder:


Run the script:

./acme.sh –install

This script also automatically creates a daily cron to check and possibly renew certificates.

Restart the terminal after installation.

Install ACME using curl or wget You can also install acme using the curl command:

curl https://get.acme.sh | sh

Or via the wget command:

wget -O – https://get.acme.sh | sh

How Is the ACME Protocol Used?

ACME is primarily used for obtaining and renewing TLS/SSL certificates. It simplifies the certificate issuance process by automating domain validation procedure, ensuring that the requester has control over the domain in question. ACME also supports various validation methods, such as HTTP-based or DNS-based challenges.

Moreover, ACME enables automated certificate renewal, eliminating the need for manual intervention. It allows servers to request certificate management actions, ensuring continuous and uninterrupted service.

ACME’s capabilities extend beyond just TLS/SSL certificates. It can be leveraged for managing other PKI (Public Key Infrastructure) certificates, such as code signing certificates and client certificates.

Why Use ACME Instead of Other Options?

SCEP and EST protocols are also used to obtain certificates.

The first one was developed by Cisco Systems. Its goal was to simplify the procedure for issuing X.509 digital certificates and make it as scalable as possible. Before the advent of SCEP, this process required the active participation of system administrators and did not scale well. Today, this protocol is one of the most common.

As for EST, it allows PKI clients to obtain certificates over secure channels. It uses TLS for messaging and issuing SSL, as well as binding the CSR to the sender. In addition, EST supports elliptic cryptography methods, which creates an additional layer of protection.

According to experts, solutions like ACME will have to be more widely adopted. They offer a simplified and secure SSL setup model and also speed up the process.

Using ACME to Automate Certificates

The ACME protocol is widely utilized for automated certificate management in the realm of web security. It provides a standardized and streamlined approach to certificate issuance, renewal, and revocation.

ACME simplifies the process of obtaining initial certificates by offering various domain validation methods. Once issued, ACME enables automated renewal, eliminating the need for manual intervention and minimizing the risk of expired certificates. In the event of a compromised or outdated certificate, ACME supports efficient revocation.

It also integrates with certificate management systems, facilitating seamless management of certificates at scale. It supports a variety of certificate types, including domain validated, organization validated, extended validation, wildcard, code signing, and client certificates.


According to the IETF, ACME will be useful for administrators who have to work with multiple domain names. The standard will help associate each of them with the desired SSL.

Among the advantages of the standard, experts also note several security mechanisms. They must ensure that SSL certificates are only issued to the real registrants. In particular, to protect against DNS attacks, a set of DNSSEC extensions is used, and to protect against DoS, the standard limits the speed of performing individual requests – for example, HTTP for the POST method. The ACME developers themselves recommend adding entropy to DNS queries and executing them from several network points to improve security.

The Importance of CA Agility

Agility allows CAs to swiftly respond to emerging trends, industry standards, and regulatory frameworks. It enables them to efficiently incorporate new encryption algorithms, cryptographic protocols, and validation methods to enhance the security and trustworthiness of digital certificates. CA agility ensures compatibility with evolving technologies such as Internet of Things (IoT), cloud computing, and mobile devices. It enables CAs to issue certificates that meet the unique needs and challenges posed by these modern digital ecosystems.

CAs that can quickly implement process improvements, automation, and streamline workflows are better equipped to handle the increasing demand for certificate issuance, revocation, and management. If CAs remain at the forefront of digital security, it is providing reliable and up-to-date certificate services that instill confidence in the online ecosystem and protect sensitive data from emerging threats.


ACME protocol stands as a powerful and adaptable solution for automated certificate management. Its standardized approach and support for various certificate types make it a crucial component in ensuring secure communication and data protection in the digital age. Helenix offers security assessments and custom development of cryptographic solutions for a wide range of organisational needs. Learn more about our competencies in the Custom Development section!


ACME challenges play a pivotal role in verifying domain ownership. This is achieved by completing specific tasks such as placing files on a web server or adding designated DNS records.

ACME, short for Automated Certificate Management Environment, operates within TLS (Transport Layer Security) to automate crucial aspects of certificate management. It streamlines the processes of obtaining, renewing, and revoking TLS/SSL certificates, ensuring secure communication.

The ACME protocol presents a myriad of advantages. These include automated certificate management, simplification of certificate renewal, support for various certificate types, and seamless integration with certificate management systems, enhancing efficiency and security.

ACME, an acronym for Automated Certificate Management Environment, signifies a protocol specifically designed for certificate management. However, it does not refer to a specific term within the realm of certificates.


  1. RFC 8555: Automatic Certificate Management Environment
  2. RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3
  3. RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
  4. RFC 8894: Simple Certificate Enrolment Protocol