X.509 Certificates

June 27, 2025
February 18, 2025

mostly using openssl tool to manage X.509 Certificates

openssl

crypto#Public-Key Cryptography Standards (PKCS)

Public key certificate - Wikiwand
X.509 - Wikiwand

X.509 — Cryptography documentation
x509 package - crypto/x509 - Go Packages

ASN.1 Made Simple - Introduction

The X.509 elephant in the certificate room: Do other certificate standards even exist? : r/crypto

X.509 数字证书与 SSL/TLS | Jckling's Blog

PKI

The authentication of server relied on Certificate Authorities (CA) and a public key infrastructure using X.509 certificates.
The server register with a CA who sign the server's public key with the key of CA for a fee. The client, after receiving the public key from server, verifies server's signature of session randoms and the certificate chain.

The Dark Side of Digital Trust

Public-Key Infrastructure (X.509) (pkix)
RFC 5280· - Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
RFC 6125 - Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)
RFC 7250 - Using Raw Public Keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
draft-ietf-cose-cbor-encoded-cert-13 - CBOR Encoded X.509 Certificates (C509 Certificates)

service-identity documentation host name verification to full RFC 6125
pyca/service-identity: Service Identity Verification for Python

Public Key Infrastructure 101 - IDManagement
Everything you should know about certificates and PKI but are too afraid to ask
Never DIY Your PKI
The State of Certificates for Identity Based Security
PKI Problems: 7 reasons why teams struggle | Keyfactor

CA/Browser Forum - Certificate Issuers, Certificate Consumers, and Interested Parties Working to Secure the Web

What’s the difference between DV, OV & EV SSL certificates?
Domain-validated certificate - Wikiwand
Extended Validation Certificate - Wikiwand
Different levels of identity checks required in TLS/SSL certificates:
Domain Validation (DV): web domain verification
Organization Validation (OV): validating a domain’s owner as well as organization type, name, status, phone number and organization blocklist check
Extended Validation (EV): adding validation of the organization’s registration number, jurisdiction, operational existence, domain fraud check and blocklist checks

Certificate Transparency (CT)

Certificate Transparency - Wikiwand
How CT Works : Certificate Transparency adds two intermediate CA
What is Certificate Transparency? | DigiCert FAQ
what is Certificate Transparency - Phind

Delegated Credentials

short living "subcerts" signed by server cert
better balance between security and reliability

Delegated credential - Wikiwand
RFC 9345 - Delegated Credentials for TLS and DTLS
Delegated Credentials for TLS
Delegated credentials: Improving TLS security - Engineering at Meta
Validating Delegated Credentials for TLS in Firefox - Mozilla Security Blog
Delegated credentials: Improving TLS security - Engineering at Meta

Keyless SSL

Cloudflare's proprietary protocol for using key server
discussion on how the server secret key is used
use Delegated Credentials instead

How does keyless SSL work? | Forward secrecy | Cloudflare
Keyless SSL: The Nitty Gritty Technical Details

Cert Revocation

OSCP and CRL, both are not ideal

Certificate revocation - Wikiwand
Online Certificate Status Protocol vs Certificate Revocation Lists
OCSP vs CRL Explained

Certificate revocation list - Wikiwand CRL covered in RFC 5280 X.509 PKI
Let’s Encrypt 的六天有效 TLS certificate 計畫 – Gea-Suan Lin's BLOG
RFC 2585 - Internet X.509 Public Key Infrastructure Operational Protocols: FTP and HTTP CRL with FTP and HTTP

Online Certificate Status Protocol - Wikiwand alternative to CRL, less data, response of status of a particular cert signed by CA
RFC 6960 - X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP
What is OCSP and how does it work? | Ascertia | Blog
SSL OCSP Exchange
The Slow Death of OCSP | Feisty Duck
Ending OCSP Support in 2025 - Let's Encrypt

Chrome does certificate revocation better | ZDNET
why standard revocation mechanism won't work, Chrome don't use OSCP

Trusted CA

Linux's trusted CA certs are store in /etc/ssl/certs/:

fd . '/etc/ssl/certs/' -e pem | xargs -d"\n" -n1 -I@ -P(nproc) openssl x509 -in @ -text -noout

Rouge CA

As it turns out, CA may not be trust-worthy after all. There are many instances of CA issuing fraudulent certificates (willingly or being hacked).

https 技术鉴赏 - YouTube
How CT Works : Certificate Transparency the issuance of cert is accompanied by a SCT record on blockchain
RFC 9162: Certificate Transparency Version 2.0
certificate-transparency/docs/SCTValidation.md at master · google/certificate-transparency · GitHub
How CT Works : Certificate Transparency
Engineering deep dive: Encoding of SCTs in certificates - Let's Encrypt
What is Certificate Transparency? - SSL Certificates - Namecheap.com

How the Comodo certificate fraud calls CA trust into question | Ars Technica

Google warns of unauthorized TLS certificates trusted by almost all OSes [Updated] | Ars Technica
Google Chrome will banish Chinese certificate authority for breach of trust | Ars Technica

Another fraudulent certificate raises the same old questions about certificate authorities | Ars Technica

Trust issues: Know the limits of SSL certificates | InfoWorld
Free public certificate authorities: Nice idea, big flaw | InfoWorld

http://arstechnica.com/search/?ie=UTF-8&q=+Certificate+Authorities

Timestamp Authority (TSA)

RFC 3161 - Internet X.509 Public Key Infrastructure Time-Stamp Protocol (TSP)
RFC 5816 - ESSCertIDv2 Update for RFC 3161
Trusted timestamping - Wikiwand
What is a timestamping authority? | Ascertia | Blog

Free Time Stamp Authority
sigstore/timestamp-authority: RFC3161 Timestamp Authority

TLS Cert

  1. go to Google
  2. view cert info
  3. export/download cert
# view cert info
openssl x509 -inform PEM -in certificate.pem -noout -text

# dump key
openssl x509 -inform PEM -in certificate.pem -pubkey -noout > public_key.pem

# For RSA keys
openssl rsa -inform PEM -pubin -in public_key.pem -modulus -noout

# For ECDSA keys
openssl ec -inform PEM -pubin -in public_key.pem -pubout -text

# For Ed25519 keys
openssl pkey -inform PEM -pubin -in public_key.pem -pubout -text

Key/Cert Types (Encodings)

X.690 - Wikiwand
BER: Basic Encoding Rules
CER: Canonical Encoding Rules
DER: Distinguished Encoding Rules

DER vs. CRT vs. CER vs. PEM Certificates and How To Convert Them
PEM, DER, CRT, and CER: X.509 Encodings and Conversions - SSL.com
tls - What's the difference between X.509 and PKCS#7 Certificate? - Information Security Stack Exchange ❗!importanpt

SSH vs. X.509 Certificates
RFC 1421 - Privacy Enhancement for Internet Electronic Mail: Part I: Message Encryption and Authentication Procedures PEM
RFC 4716 - The Secure Shell (SSH) Public Key File Format use ssh-keygen to generate/convert OpenSSH keys

Appendix A: MIME Types — OpenSSL PKI Tutorial

Matching a Private Key to a Public Key

key: no meta data, just the prime numbers and modulus
cert: with meta data

X.509 is the PKI protocol and defines the actual certificate (container) format
DER, PEM, PKCS#7, PKCS#8, PKCS#12 are encoding standards

PEM (Privacy Enhanced Mail) base64 DER, with text headers and footers
File extensions: .pem, .key, .csr, .crt
DER (Distinguished Encoding Rules), binary without text headers and footers
File extensions: .der, .cer
PKCS (Public-Key Cryptography Standards)
File extensions: .p7b (PKCS#7/CMS), .pfx, .p12 (PKCS#12 binary), .csr (PKCS#10 base64), .req (PKCS#10)

# view cert
openssl x509 -in cert.pem -text -noout

# match public and private key
openssl x509 -in cert.pem -noout -modulus
openssl rsa -in privkey.pem -noout -modulus
# regenerate public key
openssl rsa -in privkey.pem -pubout

Ciphers

Using Shangmi algorithms
Structure Analysis and Generation of X.509 Digital Certificate Based on National Secret - IOPscience
An example of a X.509 certificate using SM2 / SM3 · GitHub

cert generation

🔐 HTTPS certificate generation explained! Now setup HTTPS for local development environment (without sudo) | Blog
How to create a .pfx/.p12 certificate file using OpenSSL – SSL Information and FAQ
HOWTO: Generate a CSR for OpenSSL – (see tools.ssl.com) – SSL Information and FAQ
ssl - How to create a self-signed certificate with openssl? - Stack Overflow
OpenSSL CSR Tool - Create Your CSR Faster | DigiCert.com

How To Create a Self-Signed SSL Certificate for Nginx in Ubuntu 16.04 | DigitalOcean

Manage sensitive data with Docker secrets | Docker Documentation

Five Tips for Using Self Signed SSL Certificates with iOS | HttpWatch BlogHttpWatch Blog also on own CA

# private key and cert (CSR in the pipeline)
openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout selfsigned.key -out selfsigned.crt

openssl genrsa -out privatekey.pem 2048 # key only
openssl req -new -key privatekey.pem -out CSR.csr # CSR only
# private key and CSR
openssl req -nodes -new -newkey rsa:2048 -keyout privatekey.key -out CSR.csr
# then sign SSH certificate (.crt) with csr
openssl x509 -req -days 365 -in CSR.csr -signkey privatekey.key -out selfsigned.crt

openssl genpkey -algorithm RSA -out privatekey.pem -pkeyopt rsa_keygen_bits:2048 # private key only
openssl rsa -pubout -in privatekey.pem -out publickey.pem

openssl genrsa -out rsa_1024_priv.pem 1024
openssl rsa -pubout -in rsa_1024_priv.pem -out rsa_1024_pub.pem

query cert

How to examine the metadata of an SSL (HTTPS/TLS) cert
SSL Certificate Tools

# X.509
openssl x509 -text -noout -in certificate.pem
openssl x509 -text -noout -in certificate.cert

# DER
openssl req -text -noout -in certificate.csr

# PKCS#12 (.pfx or .p12)
openssl pkcs12 -info -in key.p12

# read RSA key
openssl rsa -in private.key -text -noout
openssl rsa -RSAPublicKey_in -in public.key -text -noout

OpenSSL Cookbook 3rd Edition - 2.5  Extracting Remote Certificates

conversion

SSL Converter - Convert SSL Certificates to different formats
Converting OpenSSH public keys - Odd Bits

# DER (.crt .cer .der) -> PEM
openssl x509 -inform der -in certificate.cer -out certificate.pem
# PEM -> DER
openssl x509 -outform der -in certificate.pem -out certificate.der
# PKCS#12 -> PEM
openssl pkcs12 -in keyStore.pfx -out keyStore.pem -nodes
#  You can add -nocerts to only output the private key or add -nokeys to only output the certificates.
# PEM -> PKCS#12
openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt