OpenBSD security features: Difference between revisions

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{{Short description|Security features as used in OpenBSD operating system}}

{{Use mdy dates|date=June 2016}}

{{Missing information|[[LibreSSL]] and the project's tendency to reduce software complexity|talksection=Suggestions for Improvement|date=AprilMay 20232025}}

{{Update|reason=OpenBSD 7.37 was released with new security features (see [https://www.openbsd.org/7377.html release notes], [https://undeadly.org/cgi?action=article;sid=20230410140049 independent news report], and [https://www.openbsd.org/innovations.html updated list of innovations])|date=April 20232025}}

The [[OpenBSD]] [[operating system]] focuses on [[computer security|security]] and the development of security features.{{r|Korff-Hope-and-Potter-2005}}{{r|Lucas-2013|p=xxvii}}{{r|Palmer-and-Nazario-2004}} According to author Michael W. Lucas, OpenBSD "is widely regarded as the most secure operating system available anywhere, under any licensing terms."{{r|Lucas-2013|p=xxix}}

== API and build changes ==

Bugs and security flaws are often caused by programmer error. A common source of error is the misuse of the <code>[[strcpy]]</code> and <code>[[strcat]]</code> [[String (computer science)|string]] functions in the [[C programming language|C]] programming language. There are two common alternatives, <code>[[strncpy]]</code> and <code>[[strncat]]</code>, but they can also be difficult to understand and easy to misuse,<ref>{{Cite web|url=http://man.openbsd.org/OpenBSD-current/man3/strncpy.3|title=strncpy – copy part of a string to another|website=OpenBSD manual pages|access-date=2021-05-14}}</ref><ref>{{Cite web|url=http://man.openbsd.org/OpenBSD-current/man3/strncat.3|title=strncat – concatenate a string with part of another|website=OpenBSD manual pages|access-date=2021-05-14}}</ref> so OpenBSD developers [[Todd C. Miller]] and [[Theo de Raadt]] designed the <code>[[strlcpy]]</code> and <code>[[strlcat]]</code> functions.<ref>{{Cite web|url=http://man.openbsd.org/OpenBSD-current/man3/strlcat.3|title=strlcpy, strlcat – size-bounded string copying and concatenation|website=OpenBSD manual pages|access-date=2021-05-14}}</ref> These functions are intended to make it harder for programmers to accidentally leave buffers unterminated or allow them to be overflowed.<ref>{{cite conference |url=http://www.usenix.org/events/usenix99/millert.html |title=strlcpy and strlcat&nbsp;- Consistent, Safe, String Copy and Concatenation |last1=Miller |first1=Todd C. |last2=de Raadt |first2=Theo |author-link2=Theo de Raadt |date=June 6, 1999 |conference=[[USENIX]] Annual Technical Conference |___location=Monterey, California |access-date=May 26, 2016}}</ref> They have been adopted by the NetBSD and FreeBSD projects but not by the [[GNU C Library]].<ref>{{cite mailing list |url=https://www.sourceware.org/ml/libc-alpha/2000-08/msg00053.html |title=Re: PATCH: safe string copy and concatenation |date=August 8, 2000 |access-date=May 26, 2016 |mailing-list=[e-mail] |last=Drepper |first=Ulrich}}</ref>

On OpenBSD, the [[Linker (computing)|linker]] has been changed to issue a warning when [[C standard library#Buffer overflow vulnerabilities|unsafe string manipulation functions]], such as <code>strcpy</code>, <code>strcat</code>, or <code>[[sprintf]]</code>, are found. All occurrences of these functions in the OpenBSD source tree have been replaced.{{citation needed|reason=This is probably in their FAQ, or at least on the mailing lists (probably tech@)|date=May 2016}} In addition, a [[Static code analysis|static bounds checker]] is included in OpenBSD in an attempt to find other common programming mistakes at compile time.<ref>{{cite mailing list |url=https://marc.info/?l=openbsd-cvs&m=105665219927976 |title=CVS: cvs.openbsd.org: src |date=June 26, 2003 |access-date=March 31, 2013 |mailing-list=openbsd-cvs |last=Madhavapeddy |first=Anil }}</ref> Other security-related [[Application programming interface|APIs]] developed by the OpenBSD project include <code>issetugid</code><ref>{{Cite web|url=http://man.openbsd.org/OpenBSD-current/man2/issetugid.2|title=issetugid – is current executable running setuid or setgid|website=OpenBSD manual pages|access-date=2021-05-14}}</ref> and <code>[[RC4#RC4-based random number generators|arc4random]]</code>.<ref>{{Cite web|url=http://man.openbsd.org/OpenBSD-current/man3/arc4random.3|title=arc4random, arc4random_buf, arc4random_uniform – random number generator|website=OpenBSD manual pages|access-date=2021-05-14}}</ref>

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In OpenBSD 5.3, support for [[full disk encryption]] was introduced,<ref>{{cite web|title=OpenBSD 5.3|url=http://www.openbsd.org/53.html|website=OpenBSD|access-date=May 26, 2016}}</ref> but enabling it during the installation of OpenBSD had required manual intervention from the user by exiting the installer and entering some commands. Starting from OpenBSD 7.3, the installer supports enabling full disk encryption using a guided procedure, not requiring manual intervention anymore.<ref>{{cite web |title=OpenBSD 7.3 |url=https://www.openbsd.org/73.html |website=www.openbsd.org |access-date=19 April 2023}}</ref><ref>{{cite web |title=Initial support for guided disk encryption in the installer |url=https://undeadly.org/cgi?action=article;sid=20230308063109 |website=undeadly.org |access-date=19 April 2023}}</ref>

To protect sensitive information such as [[password]]s from leaking on to disk, where they can persist for many years, OpenBSD supports encryption of swap space. The swap space is split up into many small regions that are each assigned their own encryption key, which is generated randomly and automatically with no input from the user, held entirely in memory, and never written to disk except when [[hibernation (computing)|hibernating]]; as soon as the data in a region is no longer required, OpenBSD discards theits encryption key, effectively transforming the data in that region into useless garbage.<ref>{{cite conference |url=https://www.usenix.org/legacy/publications/library/proceedings/sec2000/provos.html |title=Encrypting Virtual Memory |last1=Provos |first1=Niels |author-link1=Niels Provos |date=August 14, 2000 |___location=Denver, Colorado |conference=9th [[USENIX]] Security Symposium |access-date=April 9, 2006 }}</ref> Toggling this feature can be done using a single ''sysctl'' configuration option, and doesn't require any prior setup, disk partitioning, or partition-related settings to be done/changed; furthermore, there is no choice of encryption parameters (such as the algorithm or key length to use), as strong parameters are always used. There is no harm and no loss of functionality with this feature, because the encryption keys used to access swapped processes are only lost when the computer crashes (e.g. power loss), after which all operating systems discard the previous contents of the memory and swap anyway, and because [[hibernation (computing)|hibernation]] continues to work as usual with this feature. This feature is enabled by default in OpenBSD 3.8 (released in November 2005) and later; OpenBSD, as of 2022, remains the only prominent operating system to have swap encrypted by default independently of disk encryption and its user-provided password. ([[Microsoft Windows|Windows]] requires{{citation needed|date=September 2023}} toggling a configuration setting that is not presented in its user-facing ''Control Panel'' and ''Settings'' apps, and other operating systems, including [[macOS]]{{citation needed|date=September 2023}}, [[FreeBSD]],<ref>{{cite web |title=Chapter 20. Storage — 20.14. Encrypting Swap |url=https://docs.freebsd.org/en/books/handbook/disks/#swap-encrypting |website=FreeBSD Documentation Portal |access-date=27 September 2023 |language=en}}</ref>, and every [[Linux kernel|Linux]]-based operating system{{citation needed|date=September 2023}}, rely on the existing disk encryption features to encrypt the swap, which often (a) need to be enabled by the user manually, (b) require setup (if disk encryption wasn't chosen during the operating system's installation) which is not as trivial to do as toggling swap encryption on OpenBSD, and (c) use the user-provided password, which users need to remember and could be weak/guessable or even extracted out of the users.)

The [[network stack]] also makes heavy use of randomization to increase security and reduce the predictability of various values that may be of use to an attacker, including [[Transmission Control Protocol|TCP]] initial sequence numbers and timestamps, and ephemeral source ports.<ref>{{Cite web|url=http://www.securityfocus.com/columnists/361|title=OpenBSD's network stack|last=Biancuzzi|first=Federico|date=October 12, 2005|publisher=[[SecurityFocus]]|access-date=December 10, 2005}}</ref> A number of features to increase network resilience and availability, including countermeasures for problems with [[Internet Control Message Protocol|ICMP]] and software for redundancy, such as [[Common Address Redundancy Protocol|CARP]] and [[pfsync]], are also included. The project was the first to disable the plain-text [[telnet]] daemon in favor of the encrypted [[Secure shell|SSH]] daemon, in 1999,<ref>{{cite web |date=10 April 1999 |first1=Theo |last1=de Raadt |author-link1=Theo de Raadt |title=disable telnet/ftp/login by default, for now |url=http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/etc/Attic/inetd.conf?rev=1.32&content-type=text/x-cvsweb-markup|work=OpenBSD}}</ref> and features other integrated cryptographic software such as [[IPsec]]. The telnet daemon was completely removed from OpenBSD in 2005<ref>{{cite web |url=http://marc.info/?l=openbsd-cvs&m=111700017509177&w=2 |quote=Removed files: libexec/telnetd |title=CVS: cvs.openbsd.org: src |first1=Theo |last1=de Raadt |author-link1= Theo de Raadt |website=OpenBSD-CVS mailing list |date=25 May 2005}}</ref> before the release of OpenBSD version 3.8.

===Signify===

The OpenBSD project had invented their own utility for cryptographic signing and verification of files, <code>signify</code>,<ref name="BSDCan 2015 signify paper">{{cite web |last1=Unangst |first1=Ted |title=signify: Securing OpenBSD From Us To You |url=https://www.openbsd.org/papers/bsdcan-signify.html |website=www.openbsd.org |publisher=BSDCan 2015 (June), Ottawa, Canada |access-date=12 July 2022 |ref=bsdcan-signify}}</ref> instead of using existing standards and software such as [[OpenPGP]] and [[GNU Privacy Guard|GnuPG]]. The creator of the <code>signify</code> utility, Ted Unangst, wrote in 2015, speaking of [[OpenPGP]] and [[GNU Privacy Guard|GnuPG]]: ''"The concerns I had using an existing tool were complexity, quality, and complexity."''<ref name="BSDCan 2015 signify paper" /> This is in line with the project's longtime tendency to reduce complexity, and [[Vulnerability (computing)#Causes|in turn, reduce the probability of vulnerabilities]] existing in the software, and help the user understand the software better and make more security-educated decisions. <code>signify</code> is integrated into the base operating system and used for verification of all releases, patches, and packages starting with OpenBSD 5.5.<ref>{{cite web |title=OpenBSD 5.5 |url=https://www.openbsd.org/55.html |website=www.openbsd.org |access-date=12 July 2022}}</ref><ref>{{cite web |title=OpenBSD: Innovations |url=https://www.openbsd.org/innovations.html |website=www.openbsd.org |ref=innovations}}</ref> In contrast, other [[Free Software]] operating systems and security-focused software tend to use [[OpenPGP]] for release verification, and as of 2022 continue to do so, including: [[Debian]], a prominent operating system that's also used as a base for other operating systems, including [[Ubuntu]];<ref>{{cite web |title=Verifying authenticity of Debian images |url=https://www.debian.org/CD/verify |website=www.debian.org |access-date=12 July 2022}}</ref> [[Kali Linux]], a specialized operating system for [[penetration testing]], security research, [[digital forensics]], and [[Reverse engineering#Software|reverse engineering]];<ref>{{cite web |title=Download Kali Linux Images Securely {{!}} Kali Linux Documentation |url=https://www.kali.org/docs/introduction/download-images-securely/ |website=Kali Linux |access-date=12 July 2022 |language=English}}</ref> [[Qubes OS]], a security-focused operating system;<ref>{{cite web |title=Verifying signatures |url=https://www.qubes-os.org/security/verifying-signatures/ |website=Qubes OS |access-date=12 July 2022 |language=en}}</ref> [[Tor Browser]], an anonymous Web browser;<ref>{{cite web |title=How can I verify Tor Browser's signature? {{!}} Tor Project {{!}} Support |url=https://support.torproject.org/tbb/how-to-verify-signature/ |website=support.torproject.org |access-date=12 July 2022}}</ref> [[SecureDrop]], a software package for journalists and whistleblowers to exchange information securely and anonymously over the Internet;<ref>{{cite web |title=Share and accept documents securely |url=https://securedrop.org/ |website=SecureDrop |publisher=Freedom of the Press Foundation |access-date=12 July 2022 |language=en}}</ref> and [[VeraCrypt]], a software program for [[on-the-fly encryption]] and [[full disk encryption]].<ref>{{cite web |title=VeraCrypt - Free Open source disk encryption with strong security for the Paranoid |url=https://veracrypt.fr/en/Digital%20Signatures.html |website=veracrypt.fr |publisher=IDRIX |access-date=12 July 2022}}</ref>