Simple Certificate Enrollment Protocol (SCEP) is an open source protocol used for facilitating the issuance of digital certificates in large-scale settings. It simplifies and automates the process of certificate issuance by providing a standardized method for devices to communicate with a trusted Certificate Authority (CA).

In this process, the user generates a key pair and sends a certificate signing request to the SCEP server along with a one-time password. The server then validates this request, signs it and makes the signed certificate available to the user. SCEP is widely used and supported by many vendors including Microsoft and Cisco.

What are the components of Simple Certificate Enrollment Protocol?

The main components of SCEP (Simple Certificate Enrollment Protocol) are:

  • SCEP Gateway API URL: This instructs devices on how to communicate with the Public Key Infrastructure (PKI). 
  • SCEP Shared Secret: This is a password shared between the SCEP server and the Certificate Authority (CA) to verify the right server for signing certificates.
  • SCEP Certificate Request: This allows managed devices to auto-enroll for certificates. The device sends a certificate enrollment through the SCEP gateway to the CA, and once authenticated, a signed certificate is deployed onto the device.
  • SCEP Signing Certificate: This is required by most Mobile Device Management systems (MDMs). It includes the entire certificate chain and is signed by the CA issuing certificates.

How does Simple Certificate Enrollment Protocol work step by step?

Here is a step-by-step process of how Simple Certificate Enrollment Protocol (SCEP) works:

  1. Defining the URL: To begin, the SCEP URL is defined in the system. This URL acts as a communication line between devices and the Certificate Authority, telling the system how to request and get a certificate from the CA.
  2. Establishing the SCEP Shared Secret: A Shared Secret is chosen and shared between the SCEP server and the CA. This is a password that allows the server to authenticate that the client legitimately represents the identities for which the certificate is being requested.
  3. Certificate Signing Request: Once the shared secret is authenticated, a Certificate Signing Request (CSR) or SCEP request is sent to the CA. This includes the detailed profile that enables automatic enrollment for certificates on the managed devices.
  4. Uploading the SCEP Signing Certificate: To ensure the certificates used are valid, a signing certificate, trusted by the CA, is uploaded and used by the devices. This signing certificate will contain the entire certificate chain which may contain the root, intermediate and server certificates.
  5. Configuration of SCEP Settings: The SCEP Configuration profile is defined and sent to the devices. The certificate type, validity period, Subject Alternative Name and other certificate settings are defined in this step.
  6. Deployment: The signed public key certificate will be sent to the requester. The requester can then use this certificate for secure communication.
  7. Auto-Enrollment: Once all of this is set up, devices can then be set to automatically enroll for certificates.
  8. CA Authentication: Once the CA validates the shared secret, the CA signs the certificates and deploys them onto the requesting client device.
  9. Secure Communication: Following successful authentication and certificate deployment, the device can now securely communicate using the signed public key certificate.

What are the use cases for Simple Certificate Enrollment Protocol?

The Simple Certificate Enrollment Protocol (SCEP) is often used for

  • Enrolling mobile devices with Mobile Device Management (MDM) systems like Microsoft Intune and Apple MDM.
  • Managing public key infrastructure certificates, where SCEP automates the complex and extensive process of information exchange and approval procedures in issuing public key infrastructure certificates.
  • Enabling mobile devices to authenticate connections between apps and enterprise systems and resources.
  • Automating the deployment and renewal of certificates on a large scale, reducing manual labor, time, errors, and thus associated operational costs. 
  • Reducing the risk of sudden system outages, breaches, Man-in-the-Middle (MITM) attacks, and maintaining certificate validity by ensuring they are not forgotten until expiration. 
  • Simplifying and accelerating the process of enrolling and deploying certificates onto devices.

What are the strengths of Simple Certificate Enrollment Protocol?

Simplicity and Automation

SCEP makes the entire process of certificate issuance and deployment simpler and easier. It automates the complex process of information exchange and approval procedures involved in issuing PKI certificates, thus saving time for the IT teams.


SCEP allows for large-scale implementation of certificates allowing enterprises to easily manage millions of certificates across all networked devices and user identities they support. 

Risk Reduction

By automating the certificate management process, SCEP significantly reduces the risk of outages, system failures, security breaches, and MITM attacks that can occur when certificates are misconfigured or forgotten until expiration.

Cost Control

The automation brought by SCEP helps IT departments control operational costs by eliminating the time-consuming and prone-to-error manual process of certificate management.

Widely Supported

SCEP is a widely supported standard, used by many manufacturers of network equipment and software, including major Mobile Device Management (MDM) systems like Microsoft Intune and Apple MDM.

Enhanced Security

By enforcing the applications of certificates (digital signatures) onto networked devices, SCEP boosts security by supporting strong, certificate-based and mutual authentication.

What are the weaknesses of Simple Certificate Enrollment Protocol?

  • Limited Support: Legacy versions of SCEP support only RSA keys.
  • Source Authentication: Although source authentication is a critical security requirement, its support is not strictly required within SCEP. This represents a major weakness in the protocol’s security architecture. 
  • Use of Shared Secret: SCEP uses a shared secret for client authentication, which should ideally be client-specific and used only once. However, the confidentiality of this shared secret is fragile as it must be included in the CSR, compromising its security.
  • Encryption of CSR: With SCEP, the entire CSR is encrypted to protect the ‘challengePassword’ field. While this adds a layer of security, it makes the entire CSR unreadable by all parties except the Certificate Authority (CA). This lack of transparency can be problematic.
  • PKI Protection Limitations: SCEP’s PKI protection mechanism also has limitations, as it doesn’t provide for the encryption and decryption of Key Pairs.
  • No Support for Certificate Management: Unlike other protocols like CMP and CMC, SCEP doesn’t offer support for certificate management tasks, such as renewal, status checking, and revocation. 
  • Limited Flexibility: SCEP lacks the flexibility that other protocols (like CMP and CMS) have due to their use of CRMF format, which supports keys usable for encryption or key agreement only. 
  • Limited Compatibility: Many new devices, particularly IoT devices, do not support SCEP, which can cause difficulties with certificate management. 
  • Protocol and Device Vulnerabilities: Based on the protocol’s design, SCEP inherits vulnerabilities found in certain devices or network setups which can lead to spoofing or even unauthorized access.

How does Simple Certificate Enrollment Protocol compare to Enrollment over Secure Transport?

SCEP and EST are both certificate management protocols, meaning they both address the need for efficient handling of digital certificates, especially in large-scale environments.


Enrollment over Secure Transport (EST) is considered more secure than SCEP. EST uses Transport Layer Security (TLS) for client-side device authentication which provides strong mutual authentication, integrity and confidentiality.

Encryption of CSR

In SCEP, the entire Certificate Signing Request (CSR) is encrypted to protect one field, the ‘challengePassword’. This makes it unreadable for all parties except the CA, even though most of its contents are not confidential. EST does not have this issue as it does not require encryption of the entire CSR.

Use of Shared Secret

SCEP uses a shared secret for client authentication, the confidentiality of which is fragile. EST does not use shared secrets, and instead uses TLS client authentication.

Complexity and Efficiency

EST seems to be simpler and more efficient than SCEP. EST uses standard HTTPS transport, which makes its implementation relatively straightforward. It is also more network friendly, and can work more smoothly with firewalls and proxies.


EST is considered more scalable and adaptable to growing network environments. 


SCEP is an older protocol and has widespread support in legacy devices and systems. EST, while growing in popularity, is a relatively newer protocol and might not be as widely supported, particularly in older systems.

While both SCEP and EST have their strengths and weaknesses, the choice between the two would depend on the specific requirements of the system being implemented, including factors like the level of security required, the scale of the network, and the type of devices being used.

How does Simple Certificate Enrollment Protocol compare to Automated Certificate Management Environment?

Simple Certificate Enrollment Protocol (SCEP) and Automated Certificate Management Environment (ACME) are both protocols designed for the management of digital certificates, but they operate differently and are designed for different use cases.

Operation and Automation

SCEP requires some manual processes, such as manually installing the certificate on the device, which can be cumbersome in large-scale deployments.

ACME, on the other hand, was specifically designed to automate the process of certificate issuance and renewal, which makes it more efficient for large-scale certificate deployment.


While SCEP uses a shared secret for client authentication, ACME relies on a more secure public key infrastructure (PKI) based authentication method. ACME uses key pairs, also known as authorization keys, for validating the certificate authority and the organization.


SCEP encrypts the entire Certificate Signing Request (CSR) to protect the ‘challengePassword’ field, which causes the whole CSR to become unreadable for all parties except the Certificate Authority (CA).

In ACME, only the necessary fields are encrypted, ensuring confidentiality where needed without compromising general readability.

Use Case

SCEP is often used for internal applications within an organization, such as securing internal communications, while ACME is typically used for securing external-facing services, such as websites, thus reducing the burden of managing SSL/TLS certificates.


ACME is a relatively newer protocol supported by fewer devices and operating systems compared to SCEP which is older and has widespread support in legacy systems.

ACME’s validation methods

ACME provides more methods to prove the control of a domain, such as HTTP, DNS, and TLS.

Remember, neither of these protocols is inherently “better” or “worse” than the other; the best choice depends on the specific use case and requirements of the user.

How does Simple Certificate Enrollment Protocol compare to Certificate Management Protocol and Certificate Management over CMS?

Simple Certificate Enrollment Protocol (SCEP), Certificate Management Protocol (CMP), and Certificate Management over CMS (CMC) are all protocols designed for digital certificate management, but they each have different functionalities and use cases.


SCEP is primarily focused on automating the process of enrolling and issuing certificates.

On the other hand, CMP and CMC are more comprehensive in their functionality, focusing not only on certificate enrollment and issuance, but also on certificate management tasks like renewal, revocation, and status checking.


In terms of security, SCEP uses a shared secret for client authentication, which has some weaknesses.

CMP and CMC typically employ more secure methods for client authentication.


SCEP protocol encrypts the entire Certificate Signing Request (CSR) to protect just the ‘challengePassword’ field, which makes the entire CSR unreadable apart from the specific Certificate Authority (CA). This is a disadvantage when transparency and CSR checking by intermediate parties like RA are needed. CMP and CMC do not have this issue.

Support for Different Key Types

SCEP supports only RSA keys, whereas CMP and CMC work with a wider range of key types, offering more flexibility.

Legacy Support

SCEP, being an older protocol, is widely supported by many legacy systems. On the other hand, CMP and CMC may not be as universally supported, particularly by older systems and applications.

Protocol Complexity

SCEP is relatively simple and has widespread implementation. CMP and CMC, while more flexible, are also more complex, which can make implementation more challenging.

The choice between SCEP, CMP, and CMC will depend on the specific needs and existing infrastructure of an organization. CMP and CMC can potentially offer more functionality, but may be more difficult to implement and less likely to be supported in certain systems and applications. On the other hand, while SCEP may not be as functionally comprehensive, it is simpler to use and widely supported.

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