A secure attention key (SAK), special attention key, or secure attention sequence (SAS)
is a special key,
key combination or sequence to be pressed on a
computer keyboard
A computer keyboard is a built-in or peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or Push-button, keys to act as Mechanical keyboard, mechanical levers or Electronic switching system, electro ...
before a
login
In computer security, logging in (or logging on, signing in, or signing on) is the process by which an individual gains access to a computer system or program by identifying and authenticating themselves.
Typically, user credential ...
screen which must, to the user, be completely trustworthy. The
operating system
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ...
kernel, which interacts directly with the hardware, or
init system is able to detect whether the secure attention key has been pressed. When this event is detected, the trusted login processing is started.
The secure attention key is designed to make
login spoofing impossible, as the kernel will suspend any program, including those masquerading as the computer's login process, before starting a trustable login operation.
Examples
Some examples are:
* : Introduced in
systemd
systemd is a software suite that provides an array of system components for Linux operating systems. The main aim is to unify service configuration and behavior across Linux distributions. Its primary component is a "system and service manage ...
v257 as a more reliable SAK for
Linux
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
distributions but may require support from the currently running
desktop environment
In computing, a desktop environment (DE) is an implementation of the desktop metaphor made of a bundle of programs running on top of a computer operating system that share a common graphical user interface (GUI), sometimes described as a graphi ...
. It is implemented as of gdm (
GNOME
A gnome () is a mythological creature and diminutive spirit in Renaissance magic and alchemy, introduced by Paracelsus in the 16th century and widely adopted by authors, including those of modern fantasy literature. They are typically depict ...
display manager) 47.
* on
X Window System
The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems.
X originated as part of Project Athena at Massachusetts Institute of Technology (MIT) in 1984. The X protocol has been at ...
immediately kills the X server (although the key combination can be disabled) and can be used to quickly and easily get back to the login prompt.
*
default sequence for
Linux
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
.
Not a true
C2-compliant SAK.
* then on
AIX
Aix or AIX may refer to:
Computing
* AIX, a line of IBM computer operating systems
*Alternate index, for an IBM Virtual Storage Access Method key-sequenced data set
* Athens Internet Exchange, a European Internet exchange point
Places Belg ...
, but it can be disabled.
* for
PLATO IV
PLATO (Programmed Logic for Automatic Teaching Operations), also known as Project Plato and Project PLATO, was the first generalized computer-assisted instruction system. Starting in 1960, it ran on the University of Illinois's ILLIAC I compu ...
in the 1970s.
*
for Windows NT.
See also
* Control-Alt-Delete
Control-Alt-Delete (often abbreviated to Ctrl+Alt+Del and sometimes called the "three-finger salute" or "Security Keys") is a computer keyboard command on IBM PC compatible computers, invoked by pressing the Delete key while holding the Control ...
* Magic SysRq key
The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low-level commands regardless of the system's state. It is often used to recover from freeze (computing), freezes, or to booting, ...
* Break key
The Break key (or the symbol ⎊) of a computer keyboard refers to breaking a Telegraphy, telegraph circuit and originated with 19th century practice. In modern usage, the key has no well-defined purpose, but while this is the case, it can be use ...
References
Computer security procedures
Computer access control
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