Glossary

AES — the standard symmetric block cipher. In this guide as AES-256-CBC, the cipher enc and PKCS#12 use. The 256 is the key length in bits.

Base64 — an encoding that carries binary data as printable text, at a cost of about a third more bytes. PEM files are base64 with header lines around them.

Basic constraints — the certificate extension that says whether the certificate may act as a CA (CA:true) and, if so, how many CA levels may sit below it (pathlen).

CA (certificate authority) — the issuer of certificates: whoever holds a CA:true certificate and signs others with its key. A public business, or two files in a lab.

Certificate — a signed document binding a public key to a name: subject, issuer, serial, dates, extensions, and the issuer's signature over all of it. Chapter 4 reads one field by field.

Chain of trust — the sequence of certificates from a leaf up through intermediates to a root, each signed by the next. Verification is walking it.

Cipher suite — the agreed recipe for a TLS connection: key exchange, signatures, bulk cipher, hash. Named in full for TLS 1.2 (ECDHE-RSA-AES256-GCM-SHA384), numbered briefly for 1.3 (TLS_AES_256_ GCM_SHA384).

CSR (certificate signing request) — the application form for a certificate: your public key and requested name, signed with your private key. The key itself never travels.

DER — the binary storage form of a certificate or key: compact, one object per file, common in Windows and Java tooling.

Distinguished name (DN) — a certificate name written as fields: CN (common name), O (organisation), OU, L, ST, C. Subjects and issuers are DNs.

EC / elliptic curve — the modern key family: small keys, fast operations, named by curve. P-256 (prime256v1) is the common one.

Fingerprint — a hash of a certificate's DER form, printed as colon-separated hex. A name for a certificate: same fingerprint, same certificate.

HMAC — a hash mixed with a secret key: proves a message came from a key-holder and arrived unchanged.

Intermediate CA — a CA signed by a root (or a higher intermediate) that does the everyday signing, keeping the root's key out of daily use. pathlen:0 ones can sign servers but no further CAs.

KDF (key derivation function) — the process that turns a password into a key. PBKDF2 is the iterated one enc -pbkdf2 and PKCS#12 use; the legacy single-round derivation in enc is the weak one.

PEM — the text storage form: base64 between -----BEGIN ...----- and -----END ...----- lines, the label naming the object. Several objects may stack in one file — that is how chain bundles work.

PKCS#7 — an envelope carrying certificates (and optionally signed data) with no private keys; the .p7b form.

PKCS#8 — the generic wrapper for private keys of any algorithm: PEM label PRIVATE KEY, or ENCRYPTED PRIVATE KEY when locked.

PKCS#12 — the suitcase format: a private key plus its certificate and chain in one password-protected binary file (.p12, .pfx).

Private key — the secret half of a key pair. Whoever holds it is, to the protocol, the owner. Protect it like one.

Provider — OpenSSL 3's pluggable source of algorithms. openssl list -providers shows which are loaded; the default provider is the usual one.

Public key — the shareable half of a key pair, carried inside certificates and used to verify signatures.

Root CA — a self-signed CA whose certificate sits in a trust store by decision rather than by proof. The anchor every chain walk ends at.

RSA — the original public-key family: keys sized in bits (2048 and up), signatures and the modulus of chapter 4's matching trick.

Salt — random bytes mixed into a key derivation or stored with a hash, so the same password yields different results in different files. The Salted__ header of an enc file is one, in the open.

SAN (Subject Alternative Name) — the extension listing the names a certificate actually covers, as DNS: and IP: entries. The list clients check; the CN is a courtesy.

Self-signed — a certificate whose issuer is itself: subject equals issuer. Roots are self-signed and trusted by decision; a server's self-signed certificate is error 18 to everyone who hasn't made that decision about it.

Serial number — an issuer's unique number for a certificate, handed out in sequence from the CA's serial file. The lab's CA started at 1000 (hex).

SNI (Server Name Indication) — the name a TLS client asks for at hello time, so a server holding many certificates can pick the right one. s_client -servername.

TLS — Transport Layer Security: the protocol that authenticates with these certificates and encrypts with fresh, ephemeral keys. Versions 1.2 and 1.3 are the living ones.

Trust store — the set of root certificates a machine or browser has decided to believe: /etc/ssl/certs on a Linux box, or one file named by -CAfile.

Verify return code — s_client's grade of the certificate it was shown: 0 is (ok); anything else is the error number of chapters 7 and 11. It grades the paper, not the connection.