Sanger and Broad definitively answer the question of whether the US shared Permissive Action Link technology with the Pakistanis (no):
The American program was created after the Sept. 11, 2001, attacks, when the Bush administration debated whether to share with Pakistan one of the crown jewels of American nuclear protection technology, known as “permissive action links,” or PALS, a system used to keep a weapon from detonating without proper codes and authorizations.
In the end, despite past federal aid to France and Russia on delicate points of nuclear security, the administration decided that it could not share the system with the Pakistanis because of legal restrictions.
In addition, the Pakistanis were suspicious that any American-made technology in their warheads could include a secret “kill switch,” enabling the Americans to turn off their weapons.
While many nuclear experts in the federal government favored offering the PALS system because they considered Pakistan’s arsenal among the world’s most vulnerable to terrorist groups, some administration officials feared that sharing the technology would teach Pakistan too much about American weaponry. The same concern kept the Clinton administration from sharing the technology with China in the early 1990s.
Officials said Washington debated sharing security techniques with Pakistan on at least two occasions — right after it detonated its first nuclear arms in 1998, and after the terrorist attack on the United States in 2001.
The debates pitted atomic scientists who favored technical sharing against federal officials at such places as the State Department who ruled that the transfers were illegal under the Nuclear Nonproliferation Treaty and under United States law.
This is an issue that has fascinated me since my buddy Todd wrote an op-ed in 1999 arguing that Pakistan’s coup illustrated the need to declassify basic information about PALs. (The more things change, eh?)
The best arguments for sharing PALs are found in Gregory Giles, “Safeguarding Undeclared Nuclear Arsenals” The Washington Quaterly 16:2, Spring 1993, 173-186 and Dan Caldwell, “Permissive Actions Links: A Description and a Proposal,” Survival, May/June 1987.