Editing Permissive action link (section)

== Usage by other states ==
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{{legend|#0000FF|[[Nuclear-weapon-free zone]]s (NWFZs)}}
{{legend|#FF0000|[[Nuclear weapons states]]}}
{{legend|#FF8800|[[Nuclear sharing]]}}
{{legend|#dddd00|Other [[Nuclear Non-Proliferation Treaty|NPT]] signatory}}
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The increase in the number of nuclear-armed states was a similar cause for concern for the United States government for reasons similar to the original impetus for PALs. Thus, since the 1960s, the US has offered its own PAL technologies to other nuclear powers.{{Citation needed|date=July 2019}} The US considered this a necessary step: if the technology were kept secret, it would only be half as effective as possible, since the other power in a conflict might not have such safety measures.
[[File:RVSN IMG 1398.JPG|thumb|right|250px|A Russian version of analogous PAL system for their program.]]
In the early 1970s, France was an early recipient of United States assistance on this critical element of nuclear security. The [[Nuclear Non-Proliferation Treaty]] (NPT) went into effect in 1970 and precluded treaty members (including the US) from directly disseminating technology related to nuclear weapons development or enhancement. In order to get around this prohibition, the US developed a legal trick: "negative guidance". French nuclear scientists would regularly brief US scientists on French developments in the field of PALs, and the US scientists would tell their French counterparts when they were not on the right track. In 1971, the US also offered its technology to the Soviet Union, which developed a similar system.

In the early 1990s, the [[People's Republic of China]] requested information to develop its own PALs.<ref>Steven M. Bellovin: ''Permissive Action Links, Nuclear Weapons, and the Prehistory of Public Key Cryptography.'' Department of Computer Science, Columbia University, April 2006. ([http://www.usenix.org/event/usenix06/tech/slides/bellovin_2006.pdf PDF; 0.1 MB] {{Webarchive|url=https://web.archive.org/web/20210901022642/https://www.usenix.org/legacy/event/usenix06/tech/slides/bellovin_2006.pdf |date=September 1, 2021 }}, retrieved on February 4, 2009).</ref> The [[Bill Clinton|Clinton]] administration believed that to do so would give too much information to the Chinese about American weapon design, and therefore, refused the request.

Following the [[dissolution of the Soviet Union]], Ukraine had on its territory the world's [[Nuclear weapons and Ukraine|third largest nuclear weapons stockpile]].<ref name="cfr">{{cite web |url=http://www.cfr.org/arms-control-disarmament-and-nonproliferation/budapest-memorandums-security-assurances-1994/p32484 |title=Budapest Memorandums on Security Assurances, 1994 |date=5 December 1994 |publisher=Council on Foreign Relations |access-date=2014-03-02 |url-status=dead |archive-url=https://web.archive.org/web/20140317182201/http://www.cfr.org/arms-control-disarmament-and-nonproliferation/budapest-memorandums-security-assurances-1994/p32484 |archive-date=March 17, 2014 |df=mdy-all }}</ref> While Ukraine had physical control of the weapons, it did not have operational control of the weapons as they were dependent on Russian-controlled electronic permissive action links and the Russian command-and-control system. In 1994, Ukraine agreed to the destruction of the weapons, and to join the NPT.<ref name=martel-1998>{{cite book |url=https://books.google.com/books?id=MNanc3lYUsQC |chapter=Why Ukraine gave up nuclear weapons: nonproliferation incentives and disincentives |author=William C. Martel |pages=88–104 |title=Pulling Back from the Nuclear Brink: Reducing and Countering Nuclear Threats |editor=Barry R. Schneider, William L. Dowdy |publisher=Psychology Press |year=1998 |isbn=9780714648569 |access-date=6 August 2014 |quote=There are some reports that Ukraine had established effective custody, but not operational control, of the cruise missiles and gravity bombs. ... By early 1994 the only barrier to Ukraine's ability to exercise full operational control over the nuclear weapons on missiles and bombers deployed on its soil was its inability to circumvent Russian permissive action links (PALs). |archive-date=March 21, 2017 |archive-url=https://web.archive.org/web/20170321050646/https://books.google.com/books?id=MNanc3lYUsQC |url-status=live }}</ref><ref name=pikayev-1994>{{cite journal |url=http://cns.miis.edu/npr/pdfs/pikaye13.pdf |title=Post-Soviet Russia and Ukraine: Who can push the Button? |author=Alexander A. Pikayev |journal=The Nonproliferation Review |volume=1 |issue=3 |pages=31–46 |date=Spring–Summer 1994 |doi=10.1080/10736709408436550 |access-date=6 August 2014 |archive-date=May 21, 2014 |archive-url=https://web.archive.org/web/20140521083227/http://cns.miis.edu/npr/pdfs/pikaye13.pdf |url-status=live }}</ref>

In 2007, the [[UK government]] revealed that its nuclear weapons were not equipped with permissive action links. Instead, the [[UK's nuclear bombs]] to be dropped by aircraft were armed by inserting a key into a simple lock similar to those used to protect bicycles from theft. The UK withdrew all air-launched bombs in 1998.<ref>{{cite news | url=http://news.bbc.co.uk/2/hi/programmes/newsnight/7097101.stm | title=Programmes &#124; Newsnight &#124; British nukes were protected by bike locks | work=BBC News | date=November 15, 2007 | access-date=April 29, 2010 | archive-date=January 17, 2010 | archive-url=https://web.archive.org/web/20100117044744/http://news.bbc.co.uk/2/hi/programmes/newsnight/7097101.stm | url-status=live }}</ref>

[[File:Military truck carrying IRBMs of Pakistani Army.jpg|thumb|left|A mobile [[Transporter erector launcher|TEL]] system equipped with [[Intermediate-range ballistic missile|IRBM]] displayed at the [[International Defence Exhibition and Seminar|IDEAS 2008]] defense exhibition in [[Karachi]], Pakistan]]
Detailed information about PAL systems design and their use is classified, although these mechanisms have been offered to Pakistan<ref>{{cite book | last = Sanger | first = David E. | title = The Inheritance | publisher = Bantam Press | year = 2009 | location = London, UK | page = 224 | isbn = 978-0-593-06417-7 }}</ref> for protection of their nuclear weapons.<ref name="New York Times">New York Times: [https://www.nytimes.com/2007/11/18/washington/18nuke.html ''U.S. Secretly Aids Pakistan in Guarding Nuclear Arms''] {{Webarchive|url=https://web.archive.org/web/20160413002205/http://www.nytimes.com/2007/11/18/washington/18nuke.html |date=April 13, 2016 }}, Accessed on February 4, 2009.</ref> In the end, the US decided that it could not do so for legal reasons; the Pakistanis were also concerned that such technology would be sabotaged by a "kill-switch" that the US could operate. However, many experts in the field of nuclear technology in the US government supported the publication of the PAL system because they considered Pakistan's arsenal as the world's most vulnerable to abuse by terrorist groups.

{{Quote|Whether it's India or Pakistan or China or Iran, the most important thing is that you want to make sure there is no unauthorized use. You want to make sure that the guys who have their hands on the weapons can't use them without proper authorization.|[[Harold Agnew]], former director of [[Los Alamos National Laboratory]]}}

In November 2007, ''[[The New York Times]]'' revealed that the US had invested $100 million since 2001 in a secret program to protect Pakistan's nuclear arsenal. Instead of transferring PAL technology, the US provided helicopters, night vision and nuclear detection devices, as well as training to Pakistani personnel in order to prevent the theft or misuse of Pakistan's nuclear material, warheads, and laboratories.<ref name="New York Times"/> According to the Pentagon officials and the U.S. military accounts, Pakistan believed to develop and code its own version of the PAL technology, and they believe to be Pakistan's nuclear arsenals to be well secured.<ref name="New York Times"/>