RFC 5280

Q: What does the Introduction section cover in RFC 5280 — X.509 PKI?

The Introduction section provides detailed technical specifications, security considerations, and implementation guidance as documented in RFC 5280 — X.509 PKI. This content is part of the BLACKLABS RFC Reference Library.

Q: What does the Certificate Structure section cover in RFC 5280 — X.509 PKI?

The Certificate Structure section provides detailed technical specifications, security considerations, and implementation guidance as documented in RFC 5280 — X.509 PKI. This content is part of the BLACKLABS RFC Reference Library.

Q: What does the Key Extensions for 3GPP section cover in RFC 5280 — X.509 PKI?

The Key Extensions for 3GPP section provides detailed technical specifications, security considerations, and implementation guidance as documented in RFC 5280 — X.509 PKI. This content is part of the BLACKLABS RFC Reference Library.

Q: What does the Certificate Path Validation section cover in RFC 5280 — X.509 PKI?

The Certificate Path Validation section provides detailed technical specifications, security considerations, and implementation guidance as documented in RFC 5280 — X.509 PKI. This content is part of the BLACKLABS RFC Reference Library.

Q: What does the CRL Profile section cover in RFC 5280 — X.509 PKI?

The CRL Profile section provides detailed technical specifications, security considerations, and implementation guidance as documented in RFC 5280 — X.509 PKI. This content is part of the BLACKLABS RFC Reference Library.

BLACKLABS

Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile

Standards Track Obsoletes: RFC 3280

May 2008

Abstract: This document profiles the X.509 v3 certificate and X.509 v2 CRL for use in the Internet PKI. It specifies the format, semantics, and processing rules for public key certificates, trust chains, and certificate revocation. This is the foundational PKI specification referenced by 3GPP TS 33.310.

Canonical source: https://www.rfc-editor.org/rfc/rfc5280 | IETF Datatracker

1. Introduction

▶

X.509 certificates bind a public key to an identity via a digital signature from a Certificate Authority (CA). RFC 5280 defines the Internet profile of X.509 v3 certificates — the format used across TLS, IPsec, S/MIME, and code signing.

3GPP TS 33.310 defines the operator PKI framework built on X.509 certificates per RFC 5280. Every NF in a 5G SBA deployment uses X.509 certificates for TLS mutual authentication on SBI interfaces.

2. Certificate Structure

▶

Field	Version	Description
tbsCertificate.version	v3 (2)	Must be v3 for extensions
tbsCertificate.serialNumber	—	Unique per CA, positive integer
tbsCertificate.signature	—	Algorithm used by CA to sign
tbsCertificate.issuer	—	CA distinguished name
tbsCertificate.validity	—	notBefore / notAfter (UTC or GeneralizedTime)
tbsCertificate.subject	—	Entity distinguished name
tbsCertificate.subjectPublicKeyInfo	—	Algorithm + public key
tbsCertificate.extensions	v3	Critical and non-critical extensions
signatureAlgorithm	—	Must match tbsCertificate.signature
signatureValue	—	CA's signature over tbsCertificate

3. Key Extensions for 3GPP

▶

The following X.509 v3 extensions are critical for 3GPP certificate profiles:

Extension	Critical	3GPP Usage
Subject Alternative Name (SAN)	SHOULD	NF FQDN — MUST match TLS SNI
Key Usage	YES	digitalSignature, keyEncipherment
Extended Key Usage (EKU)	NO	id-kp-serverAuth, id-kp-clientAuth for mutual TLS
Basic Constraints	YES	CA:TRUE for CA certs, absent for end-entity
Authority Key Identifier	NO	Links to issuer's key for chain building
Subject Key Identifier	NO	Hash of subject's public key
CRL Distribution Points	NO	URL(s) for CRL retrieval
Authority Information Access	NO	OCSP responder URL, CA issuer URL

4. Certificate Path Validation

▶

RFC 5280 §6 defines the certificate path validation algorithm. For each certificate in the chain from end-entity to trust anchor:

Signature verification: Verify issuer's signature on the certificate
Validity period: Check notBefore ≤ current time ≤ notAfter
Revocation status: Check CRL or OCSP for revocation
Name chaining: Subject of issuer must match Issuer field
Policy processing: Certificate policies must be acceptable
Constraints: Name constraints, path length constraints, basic constraints
Key usage: CA certificates MUST have keyCertSign in keyUsage

3GPP Trust Anchor: TS 33.310 §6.1 specifies the operator root CA as the trust anchor. Each operator maintains its own PKI hierarchy. Cross-certification between operators uses bridge CAs or explicit trust.

5. CRL Profile

▶

Certificate Revocation Lists (CRLs) are signed lists of revoked certificate serial numbers, published periodically by the CA:

Full CRL: Complete list of all revoked certificates — can grow large
Delta CRL: Contains only changes since last full CRL — more efficient
CRL Distribution Points: HTTP/LDAP URLs in the certificate extension for retrieval
Revocation reasons: keyCompromise, cACompromise, affiliationChanged, superseded, cessationOfOperation

6. Security Considerations

▶

CAs must protect private keys — HSM usage recommended for operator CAs
Certificate validity periods should balance security (shorter) vs operational overhead (longer)
Revocation checking is critical — stale CRLs or unreachable OCSP can create outages
Wildcard certificates should be avoided in operator core networks for least-privilege