1. Building PKI Infrastructure

Scenarios: 6
FFI Functions: ~45
Status: ⏳ Planned

This category encompasses all scenarios for building and managing a Post-Quantum-capable Public Key Infrastructure (PKI). From creating a Root CA through multi-tier CA hierarchies to configuring revocation services (CRL/OCSP).

Scenarios

ID	Scenario	Description	Complexity	Status
1.1	Create Root CA	Self-signed Root CA with ML-DSA-65	⭐⭐⭐⭐	⏳
1.2	Create Intermediate CA	Subordinate CA signed by Root	⭐⭐⭐	⏳
1.3	Build CA Hierarchy	Multi-tier PKI structure	⭐⭐⭐⭐	⏳
1.4	Configure Trust Store	Manage trusted CAs	⭐⭐	⏳
1.5	Define Certificate Policy	Establish issuance policies	⭐⭐⭐	⏳
1.6	CRL/OCSP Infrastructure	Set up revocation services	⭐⭐⭐⭐	⏳

Architecture Overview

flowchart TB subgraph ROOT["🔐 Root CA (Scenario 1.1)"] R[("Root CA
ML-DSA-65/87
20 Years")] end subgraph INTERMEDIATE["📜 Intermediate CAs (Scenario 1.2)"] I1["Intermediate CA
Server
10 Years"] I2["Intermediate CA
Client
10 Years"] I3["Intermediate CA
CodeSign
10 Years"] end subgraph ENDENTITY["🎫 End-Entity Certificates"] E1["Server Certs
TLS/HTTPS"] E2["Client Certs
mTLS/Auth"] E3["CodeSign Certs
Signing"] end R -->|signs| I1 R -->|signs| I2 R -->|signs| I3 I1 -->|issues| E1 I2 -->|issues| E2 I3 -->|issues| E3 subgraph TRUST["🛡️ Trust Store (Scenario 1.4)"] T1["Root CA Certificates"] T2["Cross-Certificates"] end subgraph REVOCATION["🚫 Revocation (Scenario 1.6)"] CRL["CRL Distribution Points"] OCSP["OCSP Responder"] end R -.->|publishes| TRUST I1 & I2 & I3 -.->|publishes| CRL I1 & I2 & I3 -.->|responds| OCSP

Industry-Specific Requirements

Different requirements for PKI lifetimes and compliance apply depending on the industry:

Industry	Root CA Validity	Specifics	Regulation
Energy/SCADA	25 Years	Wind turbine lifetime, offline CRL	NIS2¹⁾, KRITIS-VO
Healthcare	20 Years	gematik OIDs, ePA compatible	GDPR Art. 32, DiGAV
Automotive	30 Years	V2X PKI, pseudonym certificates	UN R155²⁾, ISO 21434
Industry 4.0	20 Years	OT/IT separation, IEC 62443	NIS2, Machine Regulation
Standard IT	15 Years	Standard enterprise PKI	BSI IT-Grundschutz

Key Types for CAs

CA Type	Recommended Algorithm	Validity	Rationale
Root CA	ML-DSA-65 or ML-DSA-87	15-25 Years	Highest security, rarely used
Intermediate CA	ML-DSA-65	8-12 Years	Balance security/performance
OCSP Responder	ML-DSA-44	1-3 Years	Frequent signing, performance critical

Hybrid Recommendation: For the transition phase, hybrid keys (ECDSA P-384 + ML-DSA-65) can be used to ensure compatibility with classical systems.

Important Extensions for CA Certificates

Root CA

Extension	Value	Critical
Basic Constraints	CA=true, pathLen=1 or 2	✅ Yes
Key Usage	keyCertSign, cRLSign	✅ Yes
Subject Key Identifier	SHA-256(publicKey)	❌ No

Intermediate CA

Extension	Value	Critical
Basic Constraints	CA=true, pathLen=0	✅ Yes
Key Usage	keyCertSign, cRLSign	✅ Yes
Subject Key Identifier	SHA-256(publicKey)	❌ No
Authority Key Identifier	SKI of Root CA	❌ No
CRL Distribution Points	URL to CRL	❌ No
Authority Info Access	OCSP URL, CA Issuers URL	❌ No
Certificate Policies	Policy OID	❌ No

Security Notes

Critical Requirements for CA Operation:

Root CA Private Key: Store offline (air-gapped HSM or encrypted USB stick in safe)
Intermediate CA Private Key: HSM or strongly encrypted with hardware token
Passwords: Minimum 20 characters, high entropy, securely stored
Audit Logging: Log all CA operations
Backup: Encrypted backups at separate locations
Key Ceremony: Documented process for Root CA operations

Never:

Store Root CA private key on networked systems
CA passwords in plain text in scripts/configs
Issue CA certificates without pathLength restriction
Use self-signed end-entity certificates in production

Typical Workflow

flowchart TB subgraph P1["1️⃣ PREPARATION"] V1["Prepare air-gapped system"] V2["Document certificate policy"] V3["Define DN structure"] V4["Plan validity periods"] end subgraph P2["2️⃣ CREATE ROOT CA"] R1["ML-DSA-65/87 key pair"] R2["Self-signed certificate"] R3["Encrypt private key"] R4["Export root certificate"] end subgraph P3["3️⃣ INTERMEDIATE CA"] I1["ML-DSA-65 key pair"] I2["Create CSR"] I3["Root signs certificate"] I4["Deploy online"] end subgraph P4["4️⃣ TRUST & REVOCATION"] T1["Configure trust stores"] T2["CRL distribution points"] T3["OCSP responder"] T4["Publish first CRL"] end subgraph P5["5️⃣ OPERATION"] B1["Issue certificates"] B2["Update CRLs"] B3["OCSP responses"] B4["Monitor audit logs"] end P1 ==> P2 ==> P3 ==> P4 ==> P5 style P1 fill:#e3f2fd style P2 fill:#e8f5e9 style P3 fill:#fff8e1 style P4 fill:#fce4ec style P5 fill:#f3e5f5

Quick Start Code

Minimal Example: Create Root CA (C#)

using WvdS.Security.Cryptography.X509Certificates.Extensions.PQ;
 
using var ctx = PqCryptoContext.Initialize();
 
// Root CA with ML-DSA-65
using var rootKey = ctx.GenerateKeyPair(PqAlgorithm.MlDsa65);
var rootDn = new DnBuilder().AddCN("My Root CA").AddO("My Org").AddC("DE").Build();
 
using var rootCert = ctx.CreateRootCertificate(rootKey, rootDn,
    validYears: 20,
    extensions: new ExtBuilder()
        .BasicConstraints(ca: true, pathLen: 1)
        .KeyUsage(KeyUsageFlags.KeyCertSign | KeyUsageFlags.CrlSign)
        .SubjectKeyIdentifier(rootKey)
        .Build()
);
 
// Save
File.WriteAllText("root-ca.crt.pem", rootCert.ToPem());
File.WriteAllText("root-ca.key.pem", rootKey.ToEncryptedPem("SecurePassword123!"));

→ Complete example: Scenario 1.1

Related Categories

Category	Relationship
2. CSR	CSR creation for Intermediate CAs
3. Issue Certificates	Sign end-entity certificates from CA
5. Validation	Validate certificates against trust store
6. Revocation	CRL/OCSP operations
11. Key Management	Manage, rotate, destroy CA keys

« ← Scenarios Overview | 1.1 Create Root CA → »

Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional

category, pki, root-ca, intermediate-ca, trust-store, crl, ocsp

¹⁾

NIS2 Directive (EU) 2022/2555: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32022L2555

²⁾

UNECE R155: https://unece.org/transport/documents/2021/03/standards/un-regulation-no-155-cyber-security-and-cyber-security