In "The Race" by James Shefter p.108 he notes the Vostok was rigged "with a cache of explosives" should a cosmonaut attempt to defect.
Mark Wade's site is contrary: That only the unmanned Vostoks had a range destruct system. Is this only a reference to the rocket and not the actual spacecraft ? Shefter also states the logical lock had 6 digits and that three were given to the cosmonaut and the other three were to be radioed, if necessary.
Kamanins Diary "Hidden Cosmos" states on the morining of launch thay checked the lock and the code was 145. Three Digits.
The logical lock was indeed real as the hull of the ship, and the prevailing story was Gagarin was given the code before the flight anyway (according to Shefter from Korolev himself).
My understanding to date is:
The lock had 6 digits on the keypad (1 to 6) but the code was only three digits to open it. The cosmonauts after Vostok 1 were given thier codes freely and they wrote them in their onboard journals just in case.
(When the lock was discontinued as a flight item isn't known for sure - Vostok 3 in the museum (Chuvash)still has one, but who knows if this panel was borrowed from another ship.) As far as the destruct on the spacecraft goes, it is very dubious.
The last paragraph here is my best "educated" guess, but I was hoping someone might have more to add.
[Edited by kyra (February 05, 2007).]