SSL/TLS Glossary: 156 Certificate and HTTPS Terms Explained

0–9

0-RTT TLS 1.3 early data: 0-RTT is a TLS 1.3 and QUIC feature that lets a returning client send application data in its very first flight, using a key from a previous session.
3DES Triple DES, TDEA: 3DES (Triple DES) is a block cipher that applies DES three times with a 64-bit block size, now treated as legacy in TLS largely because of the Sweet32 attack.

A

ACME Automatic Certificate Management Environment: ACME is the IETF protocol, RFC 8555, that lets software automatically prove domain control to a CA and obtain, renew and revoke certificates.
ACME Profile ACME certificate profile: An ACME profile is a named certificate template a CA advertises in its ACME directory, letting the client choose lifetime and contents per order.
AEAD Authenticated Encryption with Associated Data: AEAD (Authenticated Encryption with Associated Data) is a class of ciphers that encrypt data and authenticate it, plus unencrypted metadata, in one operation.
AES-GCM AES in Galois/Counter Mode: AES-GCM is the AES block cipher used in Galois/Counter Mode, an AEAD construction that encrypts in counter mode and authenticates with a GHASH-based tag.
ALPN Application-Layer Protocol Negotiation: ALPN is a TLS extension that lets client and server agree on the application protocol, such as h2 or http/1.1, inside the TLS handshake.
ARI ACME Renewal Information: ARI is an ACME extension, RFC 9773, in which the CA tells each client the time window in which it should renew a specific certificate.
Authority Information Access AIA: Authority Information Access (AIA) is the X.509 extension giving URLs for the issuing CA's certificate and, optionally, the CA's OCSP responder.

B

Baseline Requirements BRs: The Baseline Requirements are the CA/Browser Forum rules every publicly trusted CA must follow when validating, issuing and revoking TLS server certificates.
Basic Constraints basicConstraints extension: Basic Constraints is the X.509 extension that states whether a certificate belongs to a CA and, optionally, how many CA levels may appear below it.
BEAST Browser Exploit Against SSL/TLS: BEAST is a 2011 attack (CVE-2011-3389) on CBC encryption in SSL 3.0 and TLS 1.0 that exploits predictable IVs to decrypt secrets such as cookies.
BIMI Brand Indicators for Message Identification: BIMI is an email specification that lets a domain publish its logo in DNS so supporting mailbox providers can show it next to authenticated messages.

C

CA Bundle CA certificate bundle: CA bundles are files of concatenated PEM certificates: either the intermediates a server must send, or the root certificates a client trusts.
CA Distrust Distrust: CA distrust is a root program's decision to stop trusting certificates from a CA, either entirely or only for certificates issued after a cut-off date.
CA/Browser Forum CA/B Forum: The CA/Browser Forum is a voluntary consortium of certificate authorities and browser vendors that sets baseline rules for publicly trusted certificates.
CAA Record Certification Authority Authorization: A CAA record is a DNS record that lists which certificate authorities may issue certificates for a domain, checked by every public CA before issuance.
CCADB Common CA Database: CCADB is the Common CA Database, a shared repository where CAs disclose their roots, intermediates, audits, policies and CRLs to root programs.
Certificate Authority CA: Certificate Authority (CA) is an organization that validates certificate requests and signs certificates binding public keys to domain names or identities.
Certificate Chain Chain of trust, certification path: Certificate chains are ordered lists of certificates, from a server's leaf through intermediates to a trusted root, each signed by the next.
Certificate Fingerprint Certificate thumbprint: Certificate fingerprints are hashes, usually SHA-256, of a certificate's DER encoding, used to identify one exact certificate; they are not stored in it.
Certificate Lifecycle Management CLM: Certificate Lifecycle Management (CLM) is the practice of discovering, issuing, deploying, renewing and revoking certificates in an automated way.
Certificate Pinning public key pinning, SSL pinning: Certificate pinning is a client-side check that accepts a server only if its certificate chain contains a specific, pre-configured certificate or public key.
Certificate Policy CP: Certificate Policy (CP) is a named set of rules for issuing and using a class of certificates, referenced by OID in the certificatePolicies extension.
Certificate Renewal: Certificate renewal is obtaining a new certificate to replace one that is about to expire, ideally automatically and with a fresh key pair.
Certificate Revocation Revocation: Certificate revocation is a CA's act of declaring an unexpired certificate invalid, published through CRLs or OCSP so that clients stop trusting it.
Certificate Serial Number Serial number: Certificate serial numbers are positive integers a CA assigns to each certificate; combined with the issuer name, they uniquely identify a certificate.
Certificate Transparency CT: Certificate Transparency is a system of public, append-only logs recording publicly trusted TLS certificates so anyone can audit what CAs issue.
Certification Practice Statement CPS: Certification Practice Statement (CPS) is a CA's public description of how it validates applicants, issues and revokes certificates, and protects its keys.
ChaCha20-Poly1305: ChaCha20-Poly1305 is an AEAD cipher pairing the ChaCha20 stream cipher with the Poly1305 authenticator, designed to be fast and constant-time in pure software.
Cipher Suite: A cipher suite is a named combination of cryptographic algorithms that a TLS client and server agree on to protect a connection, such as TLS_AES_128_GCM_SHA256.
Client Certificate TLS client authentication certificate: Client certificates are X.509 certificates that a TLS client presents during the handshake to prove its identity to the server.
Code Signing Certificate Software signing certificate: Code signing certificates are X.509 certificates with the codeSigning extended key usage, used to sign software so users can verify its publisher and integrity.
Common Name CN: Common Name (CN) is the subject attribute that once held a certificate's hostname; browsers now ignore it and match names only against the SAN list.
CRIME Compression Ratio Info-leak Made Easy: CRIME is a 2012 attack (CVE-2012-4929) that recovers secrets such as cookies by observing how TLS-level compression changes ciphertext length.
CRL Certificate Revocation List: A CRL is a list, signed and periodically reissued by a CA, of the serial numbers of certificates it revoked before their expiry date.
CRLite: CRLite is Mozilla's compact revocation dataset that lets Firefox check locally, without asking the CA, whether a publicly logged certificate is revoked.
Cross-Signing Cross-certificate: Cross-signing is when an already-trusted CA issues a certificate for another CA's key, letting that CA's certificates chain to roots older clients trust.
CRT File .crt / .cer certificate file: CRT files (.crt, also .cer) hold an X.509 certificate, encoded either as PEM text or as binary DER depending on the platform that produced them.
CSR Certificate Signing Request: A CSR (Certificate Signing Request) is a signed message with a public key and requested identity details that an applicant sends to a CA to get a certificate.
CT Log Certificate Transparency log: A CT log is a publicly auditable, append-only server that records certificates in a Merkle tree and issues signed timestamps promising to include them.

D

DANE DNS-Based Authentication of Named Entities: DANE is a protocol that uses DNSSEC-signed TLSA records to bind a TLS server's certificate or public key to its domain name.
DER Distinguished Encoding Rules: DER (Distinguished Encoding Rules) is the binary ASN.1 encoding that gives every value exactly one byte representation, used for X.509 certificates and keys.
DH Parameters dhparam, Diffie-Hellman group parameters: DH parameters are the prime modulus and generator that define a finite-field Diffie-Hellman group, which a TLS server needs in order to offer DHE cipher suites.
Diffie-Hellman DH key exchange; DHE when ephemeral: Diffie-Hellman is a key-agreement method, published in 1976, that lets two parties derive a shared secret over a public channel without ever transmitting it.
Digital Signature: A digital signature is a value computed over a message with a private key that anyone holding the matching public key can verify, proving origin and integrity.
Distinguished Name DN: Distinguished Name (DN) is the structured X.500-style name, built from attributes such as C, O and CN, that identifies a certificate's subject and issuer.
DNS-01 Challenge DNS-01: DNS-01 is an ACME challenge in which the client proves domain control by publishing a CA-derived value in a TXT record at _acme-challenge.
DNSSEC DNS Security Extensions: DNSSEC is a set of DNS extensions that lets resolvers verify, through a chain of signatures from the root zone, that DNS answers are authentic and unmodified.
Domain Control Validation DCV: Domain control validation (DCV) is the check a CA performs to confirm that a certificate applicant controls each domain name the certificate will contain.
Downgrade Attack protocol downgrade, version rollback: A downgrade attack forces a client and server to negotiate an older protocol version or weaker cipher than both support, so its weaknesses can be exploited.
DROWN Decrypting RSA with Obsolete and Weakened eNcryption: DROWN is a 2016 cross-protocol attack (CVE-2016-0800) that uses any server supporting SSLv2 to decrypt TLS sessions protected by the same RSA key.
DV Certificate Domain Validated certificate: DV certificates are TLS certificates for which the CA has verified only that the applicant controls the domain name, not who the applicant is.

E

ECC Elliptic Curve Cryptography: ECC (Elliptic Curve Cryptography) is public-key cryptography based on elliptic curves over finite fields, giving strong security with small keys.
ECDHE Elliptic Curve Diffie-Hellman Ephemeral: ECDHE (Elliptic Curve Diffie-Hellman Ephemeral) is a TLS key exchange in which both peers use fresh elliptic-curve key pairs for every handshake.
ECDSA Elliptic Curve Digital Signature Algorithm: ECDSA (Elliptic Curve Digital Signature Algorithm) is an elliptic-curve signature scheme used in TLS certificates as a smaller, faster alternative to RSA.
ECH Encrypted Client Hello: ECH (Encrypted Client Hello) is a TLS 1.3 extension that encrypts the sensitive parts of the ClientHello, including SNI, with a public key published in DNS.
Ed25519 EdDSA over Curve25519: Ed25519 is the EdDSA signature scheme on the Edwards form of Curve25519, defined in RFC 8032, with 32-byte public keys and 64-byte deterministic signatures.
eIDAS EU Regulation on electronic identification and trust services: eIDAS is the EU regulation on electronic identification and trust services, covering e-signatures, e-seals, timestamps and website authentication.
ESNI Encrypted Server Name Indication: ESNI (Encrypted SNI) is an abandoned TLS 1.3 draft that encrypted only the SNI field with a key published in DNS; it has been superseded by ECH.
EV Certificate Extended Validation certificate: EV certificates are TLS certificates issued after the strictest identity vetting, as defined by the CA/Browser Forum's Extended Validation Guidelines.
Extended Key Usage EKU: Extended Key Usage (EKU) is the X.509 extension listing the purposes a certificate may serve, such as serverAuth, clientAuth or codeSigning.
External Account Binding EAB: External Account Binding (EAB) is an ACME feature that links a new ACME account to an existing customer account at the CA using a key ID and HMAC key.

F

Forward Secrecy Perfect Forward Secrecy (PFS): Forward secrecy is a property of key exchange whereby compromise of a server's long-term private key does not expose the session keys of past connections.
FREAK Factoring RSA Export Keys: FREAK is a 2015 attack in which a man-in-the-middle tricks vulnerable TLS clients into accepting a 512-bit export-grade RSA key that can be factored.
Fullchain fullchain.pem: Fullchain is a PEM file containing the server's leaf certificate followed by the intermediate certificates needed to link it to a trusted root.

H

Hash Function cryptographic hash function: A cryptographic hash function maps input of any length to a fixed-size digest in a way that is infeasible to reverse or to make two inputs collide.
Heartbleed CVE-2014-0160: Heartbleed is a 2014 OpenSSL bug (CVE-2014-0160) in the TLS heartbeat extension that let anyone read chunks of server memory, including private keys.
HPKP HTTP Public Key Pinning: HPKP is a deprecated HTTP header, defined in RFC 7469, that told browsers to accept a site only if its chain contained a pinned public key.
HSM Hardware Security Module: HSM is a tamper-resistant hardware device that generates, stores and uses cryptographic keys internally so that private keys never leave it in plaintext.
HSTS HTTP Strict Transport Security: HSTS is an HTTP response header that tells browsers to reach a site only over HTTPS for a set period and to refuse to bypass certificate errors there.
HSTS Preload HSTS preload list: HSTS preload is a list of domains built into browsers that are always contacted over HTTPS, protecting even the first visit before any HSTS header is seen.
HTTP-01 Challenge HTTP-01: HTTP-01 is an ACME challenge in which the client proves domain control by serving a CA-specified token over plain HTTP on port 80.
HTTPS HTTP over TLS: HTTPS is HTTP carried over a TLS connection, normally on port 443, so page content, cookies and form data are encrypted and the server is authenticated.
Hybrid Key Exchange hybrid post-quantum key exchange: Hybrid key exchange combines a classical algorithm such as X25519 with a post-quantum KEM such as ML-KEM, so the result is secure unless both are broken.

I

Intermediate Certificate Intermediate CA certificate: Intermediate certificates are CA certificates, signed by a root, that issue end-entity certificates and must be served alongside the server's certificate.
IP Address Certificate IP SSL certificate: IP address certificates are TLS certificates whose SAN lists IP addresses, so clients can verify a server reached by IP rather than by domain name.

J

JKS Java KeyStore: JKS (Java KeyStore) is Java's original proprietary file format for storing private keys, certificate chains and trusted certificates, managed with keytool.

K

Key Exchange key establishment, key agreement: Key exchange is the TLS handshake step in which client and server establish a shared secret from which the connection's symmetric keys are derived.
KEY File .key file: KEY files (.key) are files that by convention hold a private key, usually PEM-encoded, though the extension says nothing about the exact format inside.
Key Rotation: Key rotation is replacing a cryptographic key with a newly generated one, on a schedule or after an incident, to limit the damage of a compromise.
Key Size Key length: Key size is a key's length in bits; its strength depends on the algorithm, so a 256-bit ECDSA key is stronger than a 2048-bit RSA key.
Key Usage keyUsage extension: Key Usage is the X.509 extension that limits the cryptographic operations a certificate's key may perform, such as signing data or signing certificates.

L

Let's Encrypt ISRG: Let's Encrypt is a free, automated, nonprofit certificate authority run by ISRG that issues domain-validated TLS certificates through the ACME protocol.
Logjam CVE-2015-4000: Logjam is a 2015 attack (CVE-2015-4000) that downgrades TLS to 512-bit export-grade Diffie-Hellman and exposes servers using small or widely shared DH groups.

M

Man-in-the-Middle Attack MITM, on-path attack: A man-in-the-middle attack is one where an attacker secretly relays, and may alter, traffic between two parties who each believe they talk directly.
Misissuance Certificate misissuance: Misissuance is any certificate issuance that breaks the Baseline Requirements or a root program policy, from flawed validation to malformed fields.
Mixed Content HTTP subresources on an HTTPS page: Mixed content is an HTTPS page that loads some subresources, such as scripts, images or iframes, over plain HTTP, undermining the page's protection.
ML-DSA Module-Lattice-Based Digital Signature Algorithm (FIPS 204): ML-DSA is the lattice-based post-quantum digital signature algorithm standardized by NIST in FIPS 204 (August 2024), derived from CRYSTALS-Dilithium.
ML-KEM Module-Lattice-Based Key-Encapsulation Mechanism (FIPS 203): ML-KEM is the post-quantum key-encapsulation mechanism standardized by NIST in FIPS 203 (August 2024), derived from CRYSTALS-Kyber.
MPIC Multi-Perspective Issuance Corroboration: MPIC is the requirement that a CA repeat domain validation and CAA checks from several network locations and issue only if enough of them agree.
mTLS Mutual TLS: mTLS (mutual TLS) is TLS in which both the server and the client authenticate each other with X.509 certificates during the handshake.
Multi-Domain Certificate SAN certificate / UCC (Unified Communications Certificate): Multi-domain certificates are TLS certificates that list several distinct hostnames in the SAN extension, so one certificate secures all of them.

N

Name Constraints nameConstraints extension: Name Constraints is an X.509 extension in CA certificates that limits which names (DNS, IP, email, DN) any certificate issued beneath that CA may contain.

O

OCSP Online Certificate Status Protocol: OCSP is a protocol, defined in RFC 6960, that lets a client ask a CA's responder whether a single certificate is currently good, revoked or unknown.
OCSP Must-Staple TLS Feature extension: OCSP Must-Staple is a certificate extension telling clients to reject the certificate if the server does not staple a valid OCSP response.
OCSP Responder OCSP server: An OCSP responder is the CA-operated server that answers OCSP requests with signed good, revoked or unknown statuses for the certificates the CA issued.
OCSP Stapling TLS Certificate Status Request: OCSP stapling lets a TLS server attach a CA-signed, time-limited OCSP response to its handshake so browsers need not query the CA themselves.
OpenSSL: OpenSSL is an open-source cryptography toolkit made up of the libssl TLS library, the libcrypto library and the openssl command-line tool.
OV Certificate Organization Validated certificate: OV certificates are TLS certificates whose CA has verified both control of the domain and the legal existence of the organization named in them.

P

P-256 secp256r1, prime256v1, NIST P-256: P-256 is a NIST elliptic curve over a 256-bit prime field, also named secp256r1 or prime256v1, widely used for ECDSA certificates and ECDHE.
PEM Privacy-Enhanced Mail encoding: PEM is a text encoding that wraps Base64-encoded DER data between BEGIN and END lines, the most common way to store certificates and keys.
PFX Personal Information Exchange (.pfx): PFX is the .pfx file that Windows and IIS use to import and export a certificate with its private key and chain, stored in PKCS #12 format.
PKCS #12 Personal Information Exchange Syntax (.p12 / .pfx): PKCS #12 is a password-protected binary container format that bundles a private key with its certificate and chain in one file, usually .p12 or .pfx.
PKCS #7 Cryptographic Message Syntax (.p7b / .p7c): PKCS #7 is a format for signed and encrypted data that, in .p7b or .p7c files, is commonly used to carry a bundle of certificates without any private key.
PKI Public Key Infrastructure: PKI (Public Key Infrastructure) is the set of roles, policies, software and procedures used to issue, distribute, validate and revoke digital certificates.
POODLE Padding Oracle On Downgraded Legacy Encryption: POODLE is a 2014 attack (CVE-2014-3566) that recovers secrets such as cookies from SSL 3.0 connections in CBC mode by abusing its unchecked padding.
Post-Quantum Cryptography PQC, quantum-resistant cryptography: Post-quantum cryptography (PQC) is public-key cryptography designed to resist attackers with large quantum computers, which could break RSA and ECC.
Precertificate CT precertificate: A precertificate is a deliberately unusable copy of a certificate, marked with a poison extension, that a CA logs in CT to obtain SCTs before final issuance.
Private CA Internal CA, enterprise CA: Private CAs are certificate authorities that an organization runs for its own systems, trusted only on devices where it installs the root.
Private Key: Private keys are the secret halves of asymmetric key pairs; in TLS, a server uses its private key to prove it owns the public key in its certificate.
PSK Pre-Shared Key: PSK (pre-shared key) in TLS is a secret both peers already hold before the handshake, used for session resumption or to authenticate without certificates.
Public Key: Public keys are the shareable halves of asymmetric key pairs, published in certificates so others can verify signatures made with the matching private key.

Q

QUIC RFC 9000 transport protocol: QUIC is a UDP-based, always-encrypted transport protocol that builds the TLS 1.3 handshake into the transport and carries HTTP/3.
QWAC Qualified Website Authentication Certificate: QWAC is a certificate issued by an EU qualified trust service provider under eIDAS that links a website to the verified legal or natural person running it.

R

RC4 Rivest Cipher 4, ARC4: RC4 is a stream cipher designed by Ron Rivest in 1987, once widely used in SSL/TLS, whose keystream biases led RFC 7465 to prohibit it in TLS in 2015.
Reverse Proxy: A reverse proxy is a server that accepts client connections on behalf of backend servers and forwards each request to them, often terminating TLS on the way.
ROBOT Return Of Bleichenbacher's Oracle Threat: ROBOT is a 2017 finding that many TLS implementations still exposed Bleichenbacher's 1998 RSA padding oracle, letting attackers decrypt RSA key exchanges.
Root Certificate Root CA certificate, trust anchor: Root certificates are self-signed CA certificates that sit at the top of a certificate chain and are pre-installed in trust stores as trust anchors.
Root Program Root store program: A root program is a browser or operating-system vendor's policy and process for deciding which root CAs its trust store includes, constrains or removes.
RSA Rivest-Shamir-Adleman: RSA is a public-key algorithm, published in 1977, that TLS uses for certificate and handshake signatures and, before TLS 1.3, for key transport.

S

S/MIME Secure/Multipurpose Internet Mail Extensions: S/MIME is a standard for signing and encrypting email messages end to end using X.509 certificates and the Cryptographic Message Syntax.
SCT Signed Certificate Timestamp: An SCT is a CT log's signed promise to add a certificate to its public log, which browsers require as proof that the certificate was submitted for logging.
Self-Signed Certificate: Self-signed certificates are certificates signed with their own private key, so issuer and subject are identical and no CA vouches for them.
Session Resumption TLS session resumption: Session resumption is a TLS mechanism that lets a client reconnect using secrets from an earlier session, skipping the full key exchange and certificate check.
Session Ticket TLS session ticket: Session tickets are encrypted blobs of TLS session state that a server hands to the client, so the client can later resume without the server storing anything.
SHA-1 Secure Hash Algorithm 1: SHA-1 is a 160-bit hash function from 1995 with practical collision attacks, so it is no longer accepted for signing publicly trusted TLS certificates.
SHA-256 SHA-2 with 256-bit output: SHA-256 is the 256-bit member of the SHA-2 hash family (NIST FIPS 180-4) and the standard hash for signing and fingerprinting TLS certificates today.
Short-Lived Certificate: Short-lived certificates are TLS certificates valid for only a few days, so expiry rather than revocation limits how long a compromised one can be misused.
SNI Server Name Indication: SNI is a TLS extension that carries the requested hostname in the ClientHello, letting one IP address serve many HTTPS sites with different certificates.
SSL Secure Sockets Layer: SSL (Secure Sockets Layer) is the original Netscape protocol for securing network connections; TLS replaced it, but the name lives on informally.
SSL 3.0 SSLv3, Secure Sockets Layer 3.0: SSL 3.0 is the last version of Netscape's Secure Sockets Layer protocol, released in 1996, broken by POODLE in 2014 and deprecated by RFC 7568 in 2015.
SSL Certificate TLS certificate: SSL certificates are CA-signed X.509 documents that bind a public key to domain names or IP addresses so that TLS clients can authenticate the server.
SSL Inspection TLS inspection, HTTPS inspection: SSL inspection is the practice of a security gateway decrypting, inspecting and re-encrypting TLS traffic, using a private CA trusted on managed devices.
SSL Offloading TLS offloading: SSL offloading is moving the CPU work of TLS handshakes and encryption from application servers to a dedicated proxy, load balancer or hardware device.
SSL Stripping HTTPS-to-HTTP downgrade: SSL stripping is a man-in-the-middle attack that keeps a victim on plain HTTP by intercepting the redirect or links that would have moved them to HTTPS.
STARTTLS opportunistic TLS upgrade: STARTTLS is a command that upgrades an existing plaintext connection in protocols such as SMTP, IMAP and POP3 to TLS on the same port.
Subject Alternative Name SAN: Subject Alternative Name (SAN) is the X.509 extension listing the DNS names, IP addresses or other identities a certificate is valid for.
Subordinate CA Sub-CA, issuing CA: Subordinate CAs are certificate authorities whose CA certificate is signed by another CA, typically a root; they usually issue end-entity certificates.
Sweet32 CVE-2016-2183: Sweet32 is a 2016 birthday attack (CVE-2016-2183) on 64-bit block ciphers such as 3DES in CBC mode that recovers secrets from very long-lived TLS connections.

T

TLS Transport Layer Security: TLS (Transport Layer Security) is the IETF standard protocol that encrypts and authenticates network connections, including every HTTPS connection.
TLS 1.0 Transport Layer Security 1.0: TLS 1.0 is the first version of Transport Layer Security, published in 1999 as RFC 2246 and formally deprecated in 2021 by RFC 8996.
TLS 1.1 Transport Layer Security 1.1: TLS 1.1 is the 2006 revision of Transport Layer Security (RFC 4346) that added explicit CBC IVs; RFC 8996 deprecated it together with TLS 1.0 in 2021.
TLS 1.2 Transport Layer Security 1.2: TLS 1.2 is the version of Transport Layer Security defined in RFC 5246 (2008) that introduced SHA-256 based key derivation and AEAD ciphers such as AES-GCM.
TLS 1.3 Transport Layer Security 1.3: TLS 1.3 is the current version of Transport Layer Security (RFC 8446 in 2018, now RFC 9846), with a one-round-trip handshake and only AEAD ciphers.
TLS Handshake: The TLS handshake is the opening exchange of a TLS connection, in which client and server agree on version and cipher, authenticate the server and derive keys.
TLS Termination SSL termination: TLS termination is the point where an incoming TLS connection ends and is decrypted, such as a CDN edge, load balancer, reverse proxy or the app server.
TLS-ALPN-01 Challenge TLS-ALPN-01: TLS-ALPN-01 is an ACME challenge where the server proves domain control on port 443 by presenting a special certificate for the acme-tls/1 protocol.
TLSA Record TLSA resource record: TLSA records are DNS records that state which certificate or public key a TLS service on a given port must present, for use by DANE.
Trust Store Root store, CA store: Trust stores are collections of root CA certificates that an operating system, browser or runtime treats as trust anchors when validating chains.

V

Validity Period notBefore / notAfter: Validity period is the time window between a certificate's notBefore and notAfter dates during which clients will accept it.
VMC Verified Mark Certificate: VMC is an X.509 certificate in which a CA verifies that an organization owns a trademarked logo, so mail clients can display it via BIMI.

W

WebTrust for CAs WebTrust audit: WebTrust for CAs is an audit framework in which licensed auditors check a CA's controls against CA/Browser Forum and root program requirements.
Wildcard Certificate Wildcard SSL certificate: Wildcard certificates are TLS certificates whose name begins with an asterisk label, such as *.example.com, matching any single-level subdomain.

X

X.509 X.509 v3 certificate: X.509 is the ITU-T standard format for public key certificates; its Internet profile, RFC 5280, defines the certificates used in TLS.
X25519MLKEM768 hybrid X25519 + ML-KEM-768 key exchange: X25519MLKEM768 is a hybrid TLS 1.3 key-exchange group that combines classical X25519 with post-quantum ML-KEM-768, used by Chrome since version 131.