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 before a login screen which must, to the user, be completely trustworthy. The operating system 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:
- Ctrl+Alt+⇧ Shift+Esc: Introduced in systemd v257 as a more reliable SAK for Linux distributions but may require support from the currently running desktop environment.3 It is implemented as of gdm (GNOME display manager) 47.4
- Ctrl+Alt+← Backspace on X Window System immediately kills the X server (although the key combination can be disabled5) and can be used to quickly and easily get back to the login prompt.6
- Alt+SysRq+K default sequence for Linux.7 Not a true C2-compliant SAK.8
- Ctrl+X then Ctrl+R on AIX9, but it can be disabled1011.
- ⇧ Shift+Stop for PLATO IV in the 1970s.12
- Ctrl+Alt+Delete for Windows NT.1314
See also
References
Lennart Poettering (2024-11-07). "Lennart Poettterin on Mastodon". Retrieved 2025-03-26. https://mastodon.social/@pid_eins/113441346864726148 ↩
Microsoft (7 January 2021). "S (Security Glossary) - Win32 apps | Microsoft Learn". Retrieved 2023-04-02. /wiki/Microsoft ↩
Lennart Poettering (2024-11-07). "Lennart Poettterin on Mastodon". Retrieved 2025-03-26. https://mastodon.social/@pid_eins/113441386934639615 ↩
Ray Strode (2024-09-11). "47.rc". Retrieved 2025-03-26. https://gitlab.gnome.org/GNOME/gdm/-/commit/969ffab4855b12d6901fc06d1a844583f294fb50 ↩
dhcp198-158 (2010-06-12). "XorgCtrlAltBackspace". Retrieved 2025-03-26.{{cite web}}: CS1 maint: numeric names: authors list (link) https://wiki.ubuntu.com/XorgCtrlAltBackspace ↩
"Enabling the Ctrl+Alt+Backspace Shortcut". Retrieved 2025-03-26. https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/desktop_migration_and_administration_guide/enable-ctrl-alt-backspace#enable-ctrl-alt-backspace ↩
Andrew Morton (2001-03-18). "Linux 2.4.2 Secure Attention Key (SAK) handling". Linux Kernel Organization. Retrieved 2011-05-30. /wiki/Andrew_Morton_(computer_programmer) ↩
"Linux Magic System Request Key Hacks". kernel.org. 2013-08-12. Retrieved 2017-05-21. https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html ↩
IBM (2025-02-03). "Using the Secure Attention Key". Retrieved 2025-03-26. https://www.ibm.com/docs/en/aix/7.3?topic=options-using-secure-attention-key ↩
IBM (2025-02-03). "Configuring the Secure Attention Key". Retrieved 2025-03-26. https://www.ibm.com/docs/en/aix/7.3?topic=options-configuring-secure-attention-key ↩
IBM (2025-02-20). "AIX Default Attributes". Retrieved 2025-03-26. https://www.ibm.com/docs/en/sig-and-i/10.0.2?topic=information-aix-default-attributes ↩
Control Data Corporation (1981-04-30). "PLATO User's Guide" (PDF). Retrieved 2023-04-21. http://www.bitsavers.org/pdf/cdc/plato/97405900C_PLATO_Users_Guide_Apr81.pdf ↩
Microsoft (7 January 2021). "S (Security Glossary) - Win32 apps | Microsoft Learn". Retrieved 2023-04-02. /wiki/Microsoft ↩
"Secure Attention Sequence (SAS) - Network Encyclopedia". 6 January 2020. Retrieved 2023-04-02. https://networkencyclopedia.com/secure-attention-sequence-sas/ ↩