Delegated Credentials : The New Standard for Securing SSL Certificate Private Keys at Scale

Large-scale websites and Content Delivery Networks (CDNs) face a fundamental security challenge when deploying SSL Certificates across hundreds or thousands of servers worldwide. To establish secure Transport Layer Security (TLS) connections with visitors, each server needs access to the SSL Certificate's private key.

Distributing this sensitive cryptographic material across numerous servers increases the risk of compromise, and a stolen private key can enable attackers to impersonate your website until the SSL Certificate expires or is revoked.

Delegated Credentials for Transport Layer Security (TLS) provide a solution to this challenge by allowing organizations to create short-lived cryptographic credentials that can terminate secure connections without exposing the primary SSL Certificate's private key.

Standardized as RFC 9345 in July 2023, Delegated Credentials represent a collaborative effort by engineers at Cloudflare, Facebook, and Mozilla to improve the security of large-scale Transport Layer Security (TLS) deployments while maintaining fast performance and operational flexibility.

This article explains what Delegated Credentials are, how they reduce private key exposure, why they matter for Content Delivery Networks (CDNs) and high-traffic environments, and what benefits and limitations this approach offers for modern web security.

Understanding the Private Key Distribution Problem

Before exploring how Delegated Credentials work, it is essential to understand the security challenge they address. The way Transport Layer Security (TLS) operates creates inherent tension between security and scalability for organizations operating large server infrastructures.

How Transport Layer Security (TLS) Connections Work

When a browser connects to a website over HTTPS, the server must prove its identity by presenting an SSL Certificate and demonstrating possession of the corresponding private key. The server uses this private key to sign messages during the Transport Layer Security (TLS) handshake, cryptographically proving that it is authorized to represent the domain specified in the SSL Certificate. Without access to the private key, a server cannot complete the handshake and establish a secure connection.

For a single server, this arrangement works well. The server stores its SSL Certificate and private key securely, uses them to terminate Transport Layer Security (TLS) connections, and the private key never needs to leave that single machine. However, modern web services rarely operate on a single server.

The Challenge of Multi-Server Deployments

Major websites like Facebook operate thousands of servers distributed across data centers worldwide. Content Delivery Networks (CDNs) like Cloudflare maintain even larger networks of edge servers designed to deliver content from locations geographically close to users. Every one of these servers needs to terminate Transport Layer Security (TLS) connections with visitors, which means every server needs access to the SSL Certificate's private key.

This requirement creates a significant security problem. Distributing the same private key to thousands of servers dramatically increases the attack surface.

An attacker who compromises any single server can potentially steal the private key and use it to impersonate the website. The attacker could perform man-in-the-middle attacks, intercepting and modifying traffic between users and the legitimate service, and this compromise would remain effective until the SSL Certificate expires or the Certificate Authority (CA) revokes it.

Traditional Approaches and Their Limitations

Organizations have attempted various approaches to mitigate this risk. Some use Hardware Security Modules (HSMs) to protect private keys, but deploying Hardware Security Modules (HSMs) at the edge of a global network is expensive and complex.

Others implement key server architectures where edge servers contact a central server to perform cryptographic operations, but this approach adds latency to every connection and creates a single point of failure.

Reducing SSL Certificate validity periods offers another potential solution. If SSL Certificates expire quickly, a stolen private key becomes useless sooner. However, short-lived SSL Certificates create operational challenges. Organizations must interact with Certificate Authorities (CAs) more frequently, and any outage at the Certificate Authority (CA) during renewal could cause the website to become unavailable.

The industry has been moving toward shorter validity periods, but even 90-day SSL Certificates leave a substantial window for attackers to exploit a compromised key.

What Are Delegated Credentials?

Delegated Credentials provide an elegant solution to the private key distribution problem by separating the long-lived SSL Certificate from the short-lived credentials used to actually terminate Transport Layer Security (TLS) connections. This approach allows organizations to keep their SSL Certificate's private key secure in a central location while distributing temporary credentials to edge servers.

The Core Concept

A Delegated Credential is a digitally signed data structure containing two essential elements : a validity interval and a public key along with its associated signature algorithm.

The SSL Certificate's private key signs this Delegated Credential, creating a cryptographic binding between the trusted SSL Certificate and the temporary credential. This signature effectively grants the Delegated Credential permission to speak on behalf of the domain names authorized in the SSL Certificate.

Think of Delegated Credentials as a limited power of attorney. The SSL Certificate owner uses their private key to authorize a Delegated Credential to terminate Transport Layer Security (TLS) connections for a specific, short period.

Edge servers use these Delegated Credentials instead of the actual SSL Certificate private key, meaning the sensitive long-lived key never needs to leave secure storage.

How the Transport Layer Security (TLS) Handshake Changes

When a browser supporting Delegated Credentials connects to a server, the handshake process differs slightly from a standard Transport Layer Security (TLS) connection.

The client includes an extension in its ClientHello message indicating support for Delegated Credentials. If the server has a valid Delegated Credential, it responds by sending both the SSL Certificate chain and the Delegated Credential.

The browser verifies that the SSL Certificate is valid and trusted, then confirms that the Delegated Credential was properly signed by the SSL Certificate's private key and has not expired. Once verified, the browser accepts the Delegated Credential's public key for the remainder of the handshake. The server proves possession of the Delegated Credential's private key, not the SSL Certificate's private key, to complete the connection.

For browsers that do not support Delegated Credentials, servers simply fall back to standard Transport Layer Security (TLS) behavior, ensuring backward compatibility with older clients.

The Seven-Day Maximum Validity

RFC 9345 specifies that Delegated Credentials may have a maximum validity period of seven days. This short lifespan is fundamental to their security model.

If an attacker compromises an edge server and steals a Delegated Credential, the window for exploitation is measured in hours or days rather than months or years.

Organizations typically generate new Delegated Credentials well before the current ones expire, often with overlapping validity periods to ensure smooth transitions. This automatic rotation happens without any involvement from Certificate Authorities (CAs), since organizations sign their own Delegated Credentials using their SSL Certificate's private key.

Security Benefits for High-Traffic Environments

Delegated Credentials offer substantial security improvements for organizations operating large Transport Layer Security (TLS) deployments. These benefits address longstanding challenges in protecting private keys while maintaining the performance and reliability that modern web services require.

Reduced Private Key Exposure

The most significant benefit of Delegated Credentials is the dramatic reduction in private key exposure.

Instead of distributing the SSL Certificate's private key to every edge server, organizations can store it in a secure central location such as a Hardware Security Module (HSM) or a carefully controlled key management system. Only the Delegated Credentials, which have their own separate key pairs, travel to edge servers.

If an attacker compromises an edge server, they obtain only the Delegated Credential's private key, not the SSL Certificate's private key. The Delegated Credential will expire within days, limiting the attacker's window of opportunity.

Meanwhile, the SSL Certificate and its private key remain secure, allowing the organization to continue operating without requesting SSL Certificate revocation or emergency reissuance.

Improved Incident Response

Traditional SSL Certificate compromises require complex incident response procedures. The organization must detect the compromise, contact the Certificate Authority (CA) to request revocation, wait for revocation information to propagate through mechanisms like Certificate Revocation Lists (CRLs) or Online Certificate Status Protocol (OCSP), and deploy a new SSL Certificate across all servers. This process can take hours or days, during which the attacker retains access to valid credentials.

With Delegated Credentials, incident response becomes simpler. If a Delegated Credential is compromised, the organization simply stops distributing new credentials to the affected server.

The compromised Delegated Credential expires within seven days at most, often sooner. No Certificate Authority (CA) involvement is required, no revocation propagation delays occur, and the SSL Certificate itself remains valid and uncompromised.

Protection During Certificate Authority (CA) Outages

Short-lived SSL Certificates create a dependency on Certificate Authority (CA) availability. If an organization uses 24-hour SSL Certificates and the Certificate Authority (CA) experiences an outage during renewal, the website becomes unavailable when the current SSL Certificate expires. This risk increases as SSL Certificate validity periods decrease.

Delegated Credentials eliminate this dependency for routine operations. The SSL Certificate can have a normal validity period of months, while Delegated Credentials provide the short-lived protection.

Since organizations generate and sign Delegated Credentials themselves, Certificate Authority (CA) availability is only required for SSL Certificate issuance and renewal, not for day-to-day operations.

Algorithm Flexibility

Certificate Authorities (CAs) sometimes lag behind in supporting new cryptographic algorithms. An organization might want to use modern signature algorithms like Ed25519, but their Certificate Authority (CA) might not support issuing SSL Certificates with these algorithms.

Delegated Credentials provide a solution because the Delegated Credential can use a different algorithm than the SSL Certificate that signed it.

This flexibility allows organizations to experiment with new algorithms without requiring Certificate Authority (CA) support.

The SSL Certificate might use a traditional algorithm like ECDSA, while the Delegated Credentials use cutting-edge algorithms. This capability supports cryptographic agility, allowing organizations to respond quickly to algorithm vulnerabilities or migrate to post-quantum algorithms when they become available.

Content Delivery Network (CDN) Implementation

Content Delivery Networks (CDNs) represent an ideal use case for Delegated Credentials. These services terminate Transport Layer Security (TLS) connections on behalf of their customers, which traditionally required customers to share their SSL Certificate private keys with the Content Delivery Network (CDN) provider.

Traditional Content Delivery Network (CDN) Security Challenges

When a website uses a Content Delivery Network (CDN) for HTTPS content delivery, the Content Delivery Network (CDN) servers must terminate Transport Layer Security (TLS) connections with visitors.

This requirement means the Content Delivery Network (CDN) needs access to the website's SSL Certificate private key. Customers must either upload their private key to the Content Delivery Network (CDN) or allow the Content Delivery Network (CDN) to generate and manage SSL Certificates on their behalf.

Sharing private keys with a third party introduces risk. The customer loses exclusive control over their cryptographic identity, and any compromise at the Content Delivery Network (CDN) could affect all customers using the service.

Some organizations with strict security requirements cannot use traditional Content Delivery Networks (CDNs) because their compliance frameworks prohibit sharing private keys with third parties.

Keyless Transport Layer Security (TLS) and Its Limitations

Cloudflare developed Keyless SSL as an earlier approach to this problem. With Keyless SSL, the Content Delivery Network (CDN) contacts a key server operated by the customer for each Transport Layer Security (TLS) handshake. The key server performs the cryptographic operations requiring the private key, and the Content Delivery Network (CDN) never actually receives the key itself.

While Keyless SSL keeps private keys secure, it introduces significant latency. Every new connection requires a round trip between the Content Delivery Network (CDN) edge server and the customer's key server, which might be located on the opposite side of the world. This latency penalty affects connection establishment time and user experience.

How Delegated Credentials Transform Content Delivery Network (CDN) Security

Delegated Credentials provide the security benefits of Keyless SSL without the latency penalty.

The customer's key server periodically generates Delegated Credentials and distributes them to the Content Delivery Network (CDN) edge servers. These Delegated Credentials allow the edge servers to terminate Transport Layer Security (TLS) connections independently, without contacting the key server for each handshake.

The customer's private key remains secure on their key server and is used only to sign new Delegated Credentials, not for every Transport Layer Security (TLS) handshake.

If the customer wants to stop using the Content Delivery Network (CDN), they simply stop issuing new Delegated Credentials. The existing Delegated Credentials expire within seven days, and the Content Delivery Network (CDN) loses the ability to represent the customer's domain.

Technical Requirements and Compatibility

Implementing Delegated Credentials requires specific technical capabilities on both the server and client side. Understanding these requirements helps organizations determine whether Delegated Credentials suit their deployment.

Transport Layer Security (TLS) 1.3 Requirement

Delegated Credentials are designed specifically for Transport Layer Security (TLS) 1.3 and later versions.

The specification explicitly warns against using Delegated Credentials with Transport Layer Security (TLS) 1.2 due to a known vulnerability. When Transport Layer Security (TLS) 1.2 servers support RSA key exchange, an attacker who can forge an RSA signature over an arbitrary message could potentially create forged Delegated Credentials valid for the entire lifetime of the SSL Certificate.

This vulnerability does not exist in Transport Layer Security (TLS) 1.3 implementations because Transport Layer Security (TLS) 1.3 removed RSA key exchange and uses exclusively ephemeral key exchange mechanisms.

Organizations must ensure their infrastructure supports Transport Layer Security (TLS) 1.3 before deploying Delegated Credentials.

SSL Certificate Extension Requirement

For an SSL Certificate to support Delegated Credentials, it must include a specific X.509 extension.

This extension has the Object Identifier (OID) 1.3.6.1.4.1.44363.44 and signals that the SSL Certificate is authorized for use with Delegated Credentials. Without this extension, browsers will not accept Delegated Credentials signed by the SSL Certificate.

Not all Certificate Authorities (CAs) currently support issuing SSL Certificates with this extension. Organizations planning to implement Delegated Credentials should verify that their Certificate Authority (CA) can include the required extension before ordering their SSL Certificate.

Some Certificate Authorities (CAs) have made code changes to support this capability, while others are still developing the necessary infrastructure.

Browser Support

Client support for Delegated Credentials is currently limited but growing. Mozilla Firefox has implemented support for Delegated Credentials, which can be enabled through the about:config preference security.tls.enable_delegated_credentials. Other browsers and Transport Layer Security (TLS) implementations are at various stages of adoption.

The limited browser support does not prevent deployment because servers can fall back to standard Transport Layer Security (TLS) behavior for clients that do not support Delegated Credentials. As browser adoption increases, more connections will benefit from the improved security model.

Limitations and Considerations

While Delegated Credentials offer significant security benefits, they also have limitations that organizations should understand before implementation.

No Revocation Mechanism

Delegated Credentials have no dedicated revocation mechanism. Once issued, a Delegated Credential remains valid until its expiration time passes. If an attacker compromises a Delegated Credential, the organization cannot immediately invalidate it the way they might request revocation of an SSL Certificate.

The short maximum validity period of seven days mitigates this limitation. The window during which a compromised Delegated Credential can be exploited is inherently limited.

Additionally, revoking the underlying SSL Certificate implicitly invalidates all Delegated Credentials signed by that SSL Certificate, providing a fallback option for severe compromises.

Infrastructure Complexity

Implementing Delegated Credentials adds complexity to Transport Layer Security (TLS) infrastructure.

Organizations need systems to generate Delegated Credentials, distribute them to edge servers, rotate them before expiration, and monitor the entire process for failures.

While this complexity is manageable for large organizations with dedicated security teams, smaller organizations might find the operational overhead challenging.

Limited Certificate Authority (CA) Support

As mentioned earlier, not all Certificate Authorities (CAs) issue SSL Certificates with the Delegated Credentials extension.

Organizations might need to work with specific Certificate Authorities (CAs) that support this capability, potentially requiring changes to existing SSL Certificate procurement processes.

Client Clock Skew Sensitivity

The short validity periods of Delegated Credentials make them sensitive to client clock skew. If a client's system clock is significantly incorrect, it might reject valid Delegated Credentials as expired or not yet valid. Servers generating Delegated Credentials should account for potential clock skew at both the beginning and end of validity periods.

Relationship to SSL Certificates

It is important to understand that Delegated Credentials complement rather than replace SSL Certificates.

Organizations still need properly validated SSL Certificates issued by trusted Certificate Authorities (CAs). The Delegated Credential derives its authority from the SSL Certificate and cannot exist independently.

The SSL Certificate Foundation

The SSL Certificate remains the foundation of trust in a Delegated Credentials deployment.

Browsers verify that the SSL Certificate is valid, properly chains to a trusted root Certificate Authority (CA), and has not been revoked. Only after accepting the SSL Certificate does the browser consider the Delegated Credential.

The validation level of the SSL Certificate carries through to the Delegated Credential. An Extended Validation (EV) SSL Certificate provides the same organizational verification guarantees whether connections are terminated using the SSL Certificate directly or through Delegated Credentials.

The Delegated Credential is bound to the SSL Certificate and can only represent the domains authorized in that SSL Certificate.

Certificate Lifecycle Considerations

SSL Certificate renewal affects Delegated Credentials deployment. When an SSL Certificate is renewed, new Delegated Credentials must be generated using the new SSL Certificate's private key.

Organizations should plan their renewal processes to ensure seamless transition between SSL Certificates without disrupting Delegated Credential distribution.

Automated Certificate Management Environment (ACME) protocols can integrate with Delegated Credentials infrastructure.

Organizations can use Automated Certificate Management Environment (ACME) to automatically obtain and renew SSL Certificates, then feed those SSL Certificates into their Delegated Credentials generation systems. This automation reduces operational burden and minimizes the risk of SSL Certificate expiration affecting service availability.

Real-World Implementations

Several major organizations have deployed Delegated Credentials in production, demonstrating the practical viability of this approach for large-scale Transport Layer Security (TLS) deployments.

Cloudflare's Deployment

Cloudflare has integrated Delegated Credentials into their Keyless SSL and Geo Key Manager products.

When customers upload SSL Certificates with the Delegated Credentials extension, Cloudflare automatically generates Delegated Credentials and distributes them to edge servers. This integration provides the security benefits of Keyless SSL without the latency penalty for clients that support Delegated Credentials.

Cloudflare periodically creates new Delegated Credentials and signs them through their Keyless infrastructure. The credentials have short lifetimes, ensuring that disabling Keyless renders all outstanding Delegated Credentials invalid within 24 hours. This approach gives customers confident control over their cryptographic identity even while using third-party edge infrastructure.

Facebook's Implementation

Facebook implemented Delegated Credentials in Fizz, their custom Transport Layer Security (TLS) 1.3 implementation.

Their deployment addresses the challenge of securing SSL Certificate private keys across thousands of servers distributed globally.

By using Delegated Credentials, Facebook can store SSL Certificate private keys in secure central locations while enabling edge servers to terminate Transport Layer Security (TLS) connections independently.

Facebook's implementation demonstrates that Delegated Credentials scale to extremely high traffic volumes. Their engineering team worked closely with the Internet Engineering Task Force (IETF) standardization process, contributing both implementation experience and specification refinements.

Future of Transport Layer Security (TLS) Security

Delegated Credentials represent one piece of the evolving Transport Layer Security (TLS) security landscape. Understanding how they fit with other developments helps organizations plan their security strategies.

Shorter SSL Certificate Validity Periods

The industry continues moving toward shorter SSL Certificate validity periods. The CA/Browser Forum has progressively reduced maximum validity from years to the current 398 days, with discussions of further reductions ongoing.

Delegated Credentials complement this trend by providing even shorter-lived credentials without the operational challenges of extremely short SSL Certificate lifetimes.

Post-Quantum Cryptography

As quantum computing advances threaten current cryptographic algorithms, the ability to use different algorithms for Delegated Credentials becomes increasingly valuable.

Organizations could potentially deploy post-quantum signature algorithms in their Delegated Credentials before Certificate Authorities (CAs) are ready to issue post-quantum SSL Certificates, providing early protection against quantum threats.

Automated SSL Certificate Management

Automated Certificate Management Environment (ACME) and similar automation technologies continue to mature, making SSL Certificate lifecycle management more reliable.

Delegated Credentials integrate well with these automation systems, allowing organizations to build fully automated infrastructures for both SSL Certificate renewal and Delegated Credential distribution.

Obtaining SSL Certificates with Delegated Credentials Support

Delegated Credentials require SSL Certificates containing a specific X.509 extension that not all Certificate Authorities (CAs) currently provide as a standard offering. This specialized requirement means organizations interested in implementing Delegated Credentials need to work with providers who can accommodate this capability.

Trustico® standard SSL Certificate products do not currently include the Delegated Credentials extension by default. However, we understand that organizations operating large-scale infrastructure, Content Delivery Networks (CDNs), or multi-server deployments may have specific requirements for this advanced functionality.

If your organization requires SSL Certificates with Delegated Credentials support, we encourage you to contact our team to discuss your specific needs. We can explore available options and work with our Certificate Authority (CA) partners to determine how best to accommodate your requirements. Our enterprise team has experience working with organizations that have specialized security and infrastructure needs, and we are committed to finding solutions that meet your technical requirements.

Frequently Asked Questions

Website administrators and security professionals often have questions about Delegated Credentials and how they apply to their specific situations.

Do Delegated Credentials Replace My SSL Certificate?

No, Delegated Credentials do not replace SSL Certificates. They work alongside SSL Certificates as a mechanism for protecting private keys in multi-server deployments.

You still need a valid SSL Certificate issued by a trusted Certificate Authority (CA), and the Delegated Credential derives its authority from that SSL Certificate.

Will Delegated Credentials Work with My Current SSL Certificate?

Delegated Credentials require SSL Certificates with a specific X.509 extension.

If your current SSL Certificate does not include this extension, you will need to obtain a new SSL Certificate from a Certificate Authority (CA) that supports Delegated Credentials.

Do All Browsers Support Delegated Credentials?

Currently, browser support for Delegated Credentials is limited.

Mozilla Firefox has implemented support, and other browsers are at various stages of development. However, servers can fall back to standard Transport Layer Security (TLS) for browsers that do not support Delegated Credentials, ensuring all visitors can connect securely.

Are Delegated Credentials Only for Large Organizations?

While Delegated Credentials were designed primarily for large-scale deployments like Content Delivery Networks (CDNs) and major websites, they can benefit any organization operating multiple Transport Layer Security (TLS) termination points.

Smaller organizations should weigh the security benefits against the infrastructure complexity before implementation.

How Often Should I Rotate Delegated Credentials?

Best practices suggest rotating Delegated Credentials well before their seven-day maximum validity expires. Many implementations use validity periods of 24 hours or less, with new credentials generated and distributed before the current ones expire. The optimal rotation frequency depends on your security requirements and infrastructure capabilities.

Does Trustico® Offer SSL Certificates with Delegated Credentials Support?

Trustico® standard SSL Certificate products do not include the Delegated Credentials extension by default. If your organization has specific requirements for Delegated Credentials functionality, please contact our team to discuss your needs. We can work with you to explore available options through our Certificate Authority (CA) partnerships.