But all sources I can see indicate Soviet weapons did indeed use PAL-equivalent security systems and there's no indication that Ukraine ever had a "fully functioning nuclear force". Some argue it would have taken a few years to acquire complete control of those within their borders had they not been handed over or destroyed. Excerpts from "The Soviet Nuclear Legacy", 1995:

>Fourth, nuclear warheads and or delivery vehicles are equipped with switches that permit arming and fusing only when a given code is entered-these devices are called permissive action links (PALs) in the USA. Launch crews do not have these enabling codes, which are provided by higher commanders prior to actual use. All categories of strategic weapons in the FSU are believed to be covered by PALs.

>To launch an ICBM, for example, now requires a '12-digit key' inserted via a complex and apparently highly secure system, and originating with the top political and military leadership. The ICBM crews do not normally have access to be able to launch missiles, but must receive a special 'preliminary' command from the top military leadership. Then they must receive additional codes that physically unblock the missiles for which they are responsible. Only when they have received these codes and commands do the crews have the physical ability to fire any of the 10 missiles in their group , . . The crews must correctly insert the codes in three tries, with an allowable time span of several seconds between each try, or else the crews are locked out and unable to perform the launch sequence. After a certain span of time has expired, the blocking system is automatically activated.

consultable at https://www.sipri.org/sites/default/files/files/RR/SIPRIRR10...