Interoperability and Future-Ready Cryptography

LAST UPDATED: JUNE 2025

This page is a living resource for ongoing interoperability testing. It aims to share knowledge, showcase current post-quantum cryptography (PQC) capabilities and interoperability between Keyfactor solutions and the broader ecosystem, and build awareness of evolving standards and use cases among PKI and signing professionals.

Disclaimer
Functionality may vary depending on the environment, platform, and software versions. While we strive to document our setup and testing environments as clearly as possible, we cannot guarantee that all features will work identically in other configurations.

Our Approach to Interoperability

We prioritize continuous integration of new cryptographic algorithms, protocols, and formats, focusing on:

Public Key Infrastructure (PKI)
Certificates for TLS/mTLS
Encryption and Key Exchange
Digital Signing and Verification
Certificate Lifecycle Management (CLM)

Through active collaboration with the wider ecosystem — including participation in industry hackathons (e.g., IETF PQC Hackathon), ACVP testing, and interoperability testing with OpenSSL, Cryptlib, WolfSSL and others — we ensure that our products remain aligned with both current and emerging needs.

Setting up Future-Ready PKI and Signing

As new post-quantum cryptography (PQC) standards are finalized, understanding their implications on PKI and signing becomes critical. This includes:

Hybrid Certificates: Combining PQC algorithms with classical algorithms (e.g., ML-KEM/RSA, ML-DSA/ECDSA).
New Key and Certificate Sizes: Affects bandwidth, storage, and performance.
New Signature Characteristics: Impacts signing speed and validation processing.

This page explores real-world interoperability use cases where these factors are critical, so engineers can plan and adopt solutions confidently.

Interoperability Test Cases and Results

Each section below highlights interoperability work per use case and lifecycle operation:
Issue, Renew/Rotate, Revoke, Sign, Encrypt, and Validate.

For each, we describe:

Why this interop matters now (e.g., upcoming standards, common real-world deployments)
Technical observations (e.g., key sizes, certificate formats, algorithm-specific behaviors)

Versions

The below interoperability tests requires specific versions of the components, equals or higher to:

Bouncy Castle 1.80 (except for private key encoding which is 1.81)
OpenSSL 3.5
EJBCA 9.3
SignServer 7.3

TLS 1.3 - Certificates and mTLS

Scope

PQC-enabled TLS 1.3 sessions
Mutual authentication (mTLS) using certificates issued by EJBCA and cryptographic libraries like OpenSSL and Bouncy Castle.
SLH-DSA has not been tested with TLS due to expectation that it will be too slow for TLS usage.

Component	Algorithms Used	Tools/Libraries	Interop Result	Notes
Certificate Issuance	ML-DSA	EJBCA, BC, OpenSSL (>=3.5)	Successful	EJBCA-issued certs validated in OpenSSL
Session Encryption	ML-KEM Key Exchange	OpenSSL, BC, Firefox, Chromium	Successful	mTLS encrypted with PQC key exchange between OpenSSL and BC
Session Authentication	ML-DSA certificates	OpenSSL, BC	Successful	mTLS authenticated with PQC certificates between OpenSSL and BC

Why this is important

TLS is foundational to secure communication. Ensuring PQC compatibility with TLS/mTLS is critical for a smooth crypto-agile transition.

Message Signing and Validation (CMS)

Scope

PQC signatures for code signing, container signing, SBOM attestations, and document signing (e.g., PDF) and time-stamping.

Component	Algorithms Used	Tools/Libraries	Interop Result	Notes
Signing	ML-DSA, SLH-DSA	SignServer, BC, OpenSSL	Successful	CMS messages signed with SignServer verified across libraries
Encryption	ML-KEM	BC, OpenSSL	Successful	Encrypted CMS messages decrypted across libraries
Time-stamping	ML-DSA	SignServer, BC	In Progress

Why this is important

Code, container, and document signing are critical to supply chain security and regulatory compliance. PQC support ensures future-proofed assurance.

Certificate Lifecycle Management (CLM)

Scope

Issuing, renewing, revoking, and managing PQC-enabled certificates.

Lifecycle Operation	Algorithms Used	Tools/Libraries	Interop Result	Notes
CSR Generation	ML-DSA, SLH-DSA, LMS	BC, EJBCA, OpenSSL	Successful	CSRs generated and processed successfully
Certificate Issuance	ML-DSA, SLH-DSA, LMS	EJBCA	Successful
Certificate Validation	ML-DSA, SLH-DSA, LMS	OpenSSL, BC	Successful
Revocation (CRL)	ML-DSA, SLH-DSA	EJBCA VA, OpenSSL, BC	Successful	CRLs issued by EJBCA validates across libraries
Revocation (OCSP)	ML-DSA	EJBCA VA, OpenSSL	Successful	OCSP responses issued by EJBCA validates across libraries
CMP	ML-KEM, ML-DSA	BC, EJBCA	Successful	CMP messages processed successfully, ML-DSA and ML-KEM certificates issued.
ACME	ML-DSA	EJBCA, CertBot	Successful	Using CertBot with a ML-DSA CSR to issue certificate from EJBCA

Why this is important

Effective CLM operations are key to maintaining security posture and trust — PQC must integrate into these lifecycles without disruption.

Storage Formats and Key Management

Scope

Testing interoperability of private keys and certificates in common formats (PEM, PKCS#12).

Format	Algorithms Used	Tools/Libraries	Interop Result	Notes
PEM Key Storage	ML-DSA, SLH-DSA	BC, OpenSSL	In Progress	Private key format for ML-DSA changed late in the IETF draft. BC 1.81 will be interoperable with OpenSSL 3.5. BC FIPS libraries will also support this in 2.2.0.
PKCS#12 Keystores	ML-DSA, SLH-DSA	BC, OpenSSL	In Progress

Why this is important

Software generated private keys need to be possible to generate with one implementation (i.e. CA generated keys) and used by another implementation (i.e. OpenSSL based Apache/NGinx).

Hybrid and Composite Certificates

Scope

Certificates combining classical and PQC algorithms for gradual migration.

Certificate Type	Algorithms Used	Tools/Libraries	Interop Result	Notes
Hybrid Certificates	ECDSA/ML-DSA	EJBCA, BC	Successful (basic)	Ongoing testing for edge cases
Composite Certificates	ECDSA/ML-DSA	(future)	Planned
PKCS#12 dual key keystores	ECDSA/ML-DSA	(future)	Planned	Dual keys and one certificate

Why this is important

If using hybrid certificates will be a valid migration process, handling all aspects including multiple private keys is critical.

Hardware Security Modules (HSMs)

Scope

PQC key operations with external HSMs.
A technical interoperability test indicated below as successful may not imply availability of commercial support in released products for all listed HSMs.

HSM Vendor	Algorithms Tested	ML-DSA External Mu	Interop Result	Notes
Fortanix Data Security Manager	ML-DSA, LMS	Not yet	Successful	Max object size to sign is limited until external-mu ML-DSA is supported.
Securosys CloudHSM	ML-DSA, LMS	Not yet	Successful	Max object size to sign is limited until external-mu ML-DSA is supported.
CryptoNext Quantum-Safe library and SDK	ML-DSA	Not yet	Successful	Software development kit and SoftHSM
Crypto4A QxEDGE	ML-DSA, LMS	Not yet	Successful	Max object size to sign is limited until external-mu ML-DSA is supported.
Thales TCT	LMS	N/A	Successful
Thales Luna			In progress
Utimaco uTrust			In progress

Why this is important

For production use cases that needs security compliance it is critical that HSMs can be used for deployments of EJBCA and SignServer.

References and External Resources

IETF drafts:

For more product Interoperability and Certification information: