> The PKI Handbook: 26 chapters in 8 parts, from symmetric keys to certificates, TLS, revocation, ACME, private CAs and post-quantum. Source: https://pkizerotohero.com/handbook/ # The PKI Handbook 26 chapters in 8 parts, from your first secret key to post-quantum cryptography. Every chapter starts in plain words, then goes as deep as you want. No account needed. 26 of 26 chapters published in this early edition. Each chapter matches one level of the game. I ## Part I: Secrets Keeping a message private: shared keys, key pairs and agreeing a secret in public. Chapter 1 ### [Symmetric encryption: one shared key](https://pkizerotohero.com/handbook/symmetric-encryption/) Symmetric encryption scrambles data with one secret key, and only someone who holds that same key can turn the scrambled data back into readable text. - Beginner - Developer - IT ops Level: Beginner Chapter 2 ### [The key-distribution problem](https://pkizerotohero.com/handbook/key-distribution/) A shared secret key must reach each partner without anyone else seeing it, and every pair needs its own key, so sharing secret keys does not scale. - Beginner - Leader - IT ops Level: Beginner Chapter 3 ### [Key pairs: public and private keys](https://pkizerotohero.com/handbook/key-pairs/) A key pair is two keys: a public key anyone may have and a private key only you hold, so strangers can encrypt to you without sharing a secret first. - Beginner - Developer - IT ops Level: Beginner Chapter 4 ### [Key exchange and hybrid encryption](https://pkizerotohero.com/handbook/key-exchange/) Two parties can agree a shared secret over an open network without ever sending it, then derive fast symmetric keys from it to protect the actual data. - Developer - IT ops - Beginner Level: Practitioner II ## Part II: Proof Proving a message is unchanged and really from its sender: hashes and signatures. Chapter 5 ### [Hashes and fingerprints](https://pkizerotohero.com/handbook/hashes/) A cryptographic hash turns any data into a short, fixed-size fingerprint; any change gives a completely different fingerprint, and you cannot run it backwards to get the data. - Beginner - Developer - IT ops Level: Beginner Chapter 6 ### [Digital signatures](https://pkizerotohero.com/handbook/digital-signatures/) A digital signature is a value only the private-key holder can compute for a message, and anyone with the public key can check that it matches that exact, unchanged message. - Beginner - Developer - IT ops Level: Practitioner Chapter 7 ### [Whose key is it? Binding identity to keys](https://pkizerotohero.com/handbook/binding-identity/) Encryption and signatures only help if you use the right person's public key, so something you already trust must vouch that a key belongs to a name. - Beginner - Developer - IT ops Level: Beginner III ## Part III: Certificates Binding a name to a public key: X.509, names, requests and validation. Chapter 8 ### [Anatomy of an X.509 certificate](https://pkizerotohero.com/handbook/x509-certificates/) An X.509 certificate is a public, signed record that ties one public key to names for a fixed period, and you can read every field with openssl. - Developer - IT ops - Beginner Level: Practitioner Chapter 9 ### [Names and jobs: SANs, wildcards, key usage and the CA flag](https://pkizerotohero.com/handbook/names-and-key-usage/) A certificate is valid only for the names in its Subject Alternative Name list, and only for the jobs that its key usage, extended key usage and CA flag allow. - Developer - IT ops - Expert Level: Practitioner Chapter 10 ### [Asking for a certificate: key generation and the CSR](https://pkizerotohero.com/handbook/csr/) You generate a key pair, keep the private key, and send the CA a certificate signing request (CSR) carrying only your public key and the names you want. - Developer - IT ops - Beginner Level: Practitioner Chapter 11 ### [Proving you own the name: DV, OV, EV and CAA](https://pkizerotohero.com/handbook/domain-validation/) Before issuing, a CA checks that you control each name, using a file, a DNS record or a TLS response, and reads CAA records; OV and EV check the organisation. - IT ops - Developer - Leader Level: Practitioner IV ## Part IV: Trust and HTTPS Trust stores, chains, cross-signing and the TLS 1.3 handshake. Chapter 12 ### [Who do we trust? CAs, trust stores and self-signed certificates](https://pkizerotohero.com/handbook/trust-stores/) Every client trusts only the root certificates in its own trust store, so a certificate is accepted only if its chain ends at one of them; being self-signed earns nothing. - Developer - IT ops - Expert Level: Practitioner Chapter 13 ### [Certificate chains and path validation](https://pkizerotohero.com/handbook/certificate-chains/) Servers must send their leaf and intermediate certificates; clients link them by name and key identifier up to a trusted root and check every signature, date and constraint. - Developer - IT ops - Expert Level: Practitioner Chapter 14 ### [Two roads to the same root: cross-signing and root expiry](https://pkizerotohero.com/handbook/cross-signing/) Cross-signing gives one CA key two certificates from different issuers, so a chain can reach either an old or a new root; clients must pick a path that is valid. - IT ops - Developer - Expert Level: Practitioner Chapter 15 ### [The TLS 1.3 handshake](https://pkizerotohero.com/handbook/tls-handshake/) In one round trip, client and server agree fresh keys with ECDHE, the server proves it holds the certificate's key by signing the handshake, and both confirm nothing was altered. - Developer - IT ops - Expert Level: Practitioner V ## Part V: When trust breaks Revocation, Certificate Transparency and what famous failures taught us. Chapter 16 ### [Taking it back: CRLs, OCSP and stapling](https://pkizerotohero.com/handbook/revocation/) Revocation lets a CA cancel a certificate before it expires, but many clients check late, softly or not at all, so short lifetimes now do much of the work. - IT ops - Expert - Developer Level: Practitioner Chapter 17 ### [Certificate Transparency](https://pkizerotohero.com/handbook/certificate-transparency/) Certificate Transparency records every publicly trusted TLS certificate in public, append-only logs, so anyone can spot a certificate for their name that they never asked for. - IT ops - Expert - Developer Level: Practitioner Chapter 18 ### [Famous failures and what changed](https://pkizerotohero.com/handbook/famous-failures/) Real PKI failures, from a hacked CA to expired certificates, follow one pattern: a weak point breaks trust, someone notices, and the rules or practices change. - IT ops - Expert - Leader Level: Practitioner VI ## Part VI: Running PKI Inventory, renewal, ACME, guarding keys and running a CA of your own. Chapter 19 ### [Inventory, expiry and renewal](https://pkizerotohero.com/handbook/certificate-lifecycle/) Every certificate expires and lifetimes keep shrinking, so you need an inventory, an owner for each certificate, monitoring of what servers really send, and automated renewal. - IT ops - Developer - Leader Level: Practitioner Chapter 20 ### [ACME and the 47-day schedule](https://pkizerotohero.com/handbook/acme/) ACME lets software prove control of a name, then fetch, renew and install certificates automatically: the only practical way to live with very short certificate lifetimes. - IT ops - Developer - Expert Level: Practitioner Chapter 21 ### [Guarding the keys: HSMs and key ceremonies](https://pkizerotohero.com/handbook/hsm-and-key-ceremonies/) A CA is only as trustworthy as its private keys, so they live in certified hardware, are created in witnessed ceremonies and are used only under multi-person control. - Expert - IT ops - Leader Level: Expert Chapter 22 ### [A CA of your own: private two-tier PKI](https://pkizerotohero.com/handbook/private-ca/) A private CA lets you issue certificates for internal systems under your own rules, built safely as an offline root plus an online issuing CA with clear policies and templates. - Expert - IT ops - Developer Level: Expert VII ## Part VII: Beyond the browser Mutual TLS, code and document signing, and device identity. Chapter 23 ### [Both sides show ID: mutual TLS](https://pkizerotohero.com/handbook/mutual-tls/) In mutual TLS the client also proves who it is, with a certificate and a signature from its private key, so both ends are authenticated before any data flows. - IT ops - Developer - Expert Level: Practitioner Chapter 24 ### [Signed and sealed: code and document signing](https://pkizerotohero.com/handbook/code-signing/) A code or document signature proves who signed a file and that nobody changed it since; a trusted timestamp keeps that proof valid after the signing certificate expires. - Developer - IT ops - Expert Level: Practitioner Chapter 25 ### [Machines with passports: device identity](https://pkizerotohero.com/handbook/device-identity/) A device certificate, installed at the factory with its private key locked in secure hardware, lets a machine prove what it is and who made it, for its whole life. - IT ops - Developer - Expert Level: Practitioner VIII ## Part VIII: The future Post-quantum cryptography and what changes next. Chapter 26 ### [Post-quantum cryptography](https://pkizerotohero.com/handbook/post-quantum/) A large quantum computer would break RSA and elliptic-curve cryptography, so key exchange is already moving to ML-KEM, and signatures and certificates come next. - Expert - Leader - IT ops Level: Practitioner A ## Appendices Reference pages to keep open while you work. ### [Glossary: PKI terms in plain words](https://pkizerotohero.com/handbook/glossary/) Every PKI and TLS term used on this site, from ACME to X.509, each with a one-line answer, a fuller explanation and the chapter that teaches it. ### [Cheat sheet: the certificate commands you actually need](https://pkizerotohero.com/handbook/cheat-sheet/) Tested OpenSSL, curl, keytool, Windows and Kubernetes commands for everyday certificate work, grouped by the task you are trying to do. ### [File formats: PEM, DER, PKCS #12 and friends](https://pkizerotohero.com/handbook/file-formats/) The formats are wrappings of the same data: DER is binary, PEM is DER in Base64, PKCS #12 bundles a key with its certificates, and PKCS #7 carries certificates only. ### [Timeline: how PKI got here](https://pkizerotohero.com/handbook/timeline/) From the first public-key papers in the 1970s to ever-shorter certificate lifetimes and post-quantum key exchange: the milestones and incidents that shaped how certificates work today. ### [Standards index: the rules behind every chapter](https://pkizerotohero.com/handbook/standards/) The RFCs, CA/Browser Forum documents, root program policies, NIST standards and EU rules that this handbook relies on, each with what it covers and where to read it.