Glossary
Explanations of SSH, authentication and networking terminology.
These definitions are for reference; details depend on the operating system, configuration and software version.
- AES
- Advanced Encryption Standard: a symmetric cipher used to protect data with a shared encryption key.
- API
- Application programming interface: a defined way for software components to communicate or use a service.
- CA
- Certificate authority: an entity whose signing key is trusted to issue certificates.
- chroot
- A process restriction that changes the directory treated as its filesystem root; it is not a complete security sandbox by itself.
- CIDR
- Classless Inter-Domain Routing: notation such as 192.0.2.0/24 that describes an address range and prefix length.
- DNS
- Domain Name System: translates domain names into network addresses and provides other domain records.
- Ed25519
- A public-key signature algorithm used by SSH keys and certificates.
- FIDO
- Fast IDentity OnlineA family of authentication standards that can use hardware security keys to protect credentials.
- fingerprint
- A compact hash-based representation of a key, used to compare and verify its identity through a trusted channel.
- GSSAPI
- Generic Security Service Application Programming InterfaceGeneric Security Services API: an interface applications can use for security mechanisms such as Kerberos.
- hash
- A computed digest that represents data; a cryptographic hash is designed to make collisions difficult to find.
- HMAC
- Hash-based message authentication code: a message authentication code constructed using a cryptographic hash.
- IP
- Internet Protocol: the addressing and packet format used to send data between networked devices.
- IPv4
- Internet Protocol version 4: the address format represented by values such as 192.0.2.10.
- IPv6
- Internet Protocol version 6: a newer address format with a much larger address space.
- Kerberos
- A network authentication system that uses tickets issued by a trusted service.
- localhost
- A name commonly resolving to a loopback address on the same device; exact resolution depends on system configuration.
- loopback
- A network address that refers back to the same device, such as 127.0.0.1 or ::1.
- MAC
- Message authentication code: a value used to check message integrity and authenticity with a shared secret.
- MFA
- Multi-factor authentication: a login process requiring at least two different kinds of proof of identity.
- OpenSSH
- An open-source implementation of SSH tools, including the ssh client and sshd server.
- OTP
- One-time password: a code intended to be used once, often as an additional login factor.
- PAM
- Pluggable Authentication Modules: a system framework that lets services use configured authentication policies, such as passwords or one-time codes.
- private key
- The secret part of a key pair, used to prove identity or sign data; it must be protected and not shared.
- PTY
- Pseudo-TerminalA pseudo-terminal: a software-created terminal used by interactive programs and remote sessions.
- public key
- The shareable part of a key pair; a server can use it to verify authentication without receiving the private key.
- root
- The administrative account on Unix-like systems, normally able to control the whole system.
- RSA
- Rivest-Shamir-AdlemanAn asymmetric cryptographic algorithm used for keys and signatures; accepted key sizes and algorithms depend on configuration.
- SCP
- Secure copy: a command for copying files over SSH; modern OpenSSH versions normally use SFTP for transfers.
- SFTP
- SSH File Transfer Protocol: transfers and manages files over an SSH connection.
- shell
- A command interpreter that reads commands and runs programs, for example a login shell on a server.
- SOCKS
- A proxy protocol that lets a configured client request connections through a proxy server; it is not a VPN.
- SSH
- Secure Shell: an encrypted protocol for connecting to and communicating with a remote computer.
- sshd
- The OpenSSH server daemon: a background service that accepts and handles SSH connections.
- syslog
- A system logging facility used to collect and route messages from services and applications.
- TCP
- Transmission Control Protocol: a network transport that delivers an ordered stream of data between endpoints.
- TLS
- Transport Layer Security: a protocol that protects network connections; SSH has its own separate protocol.
- TOTP
- Time-based one-time password: a type of OTP generated from a shared secret and the current time; the code changes periodically.
- TTY
- TeletypewriterA terminal device: an interface that lets a user interact with a command-line session.
- UDP
- User Datagram Protocol: a network transport that sends individual packets without guaranteeing delivery or order.
- Unix
- A family of operating systems and related design conventions; macOS and many server systems provide Unix-style interfaces.
- VPN
- Virtual private network: a network tunnel that can route selected network traffic through another network.
- X11
- X Window System, Version 11A window-system protocol that can display graphical applications across a network.