King breaks security code that is one digit (6)
I believe the answer is:
pinkie
'one digit' is the definition.
(I know that pinkie is a type of finger)
'king breaks security code that is' is the wordplay.
'king' becomes 'K' (chess abbreviation).
'breaks' indicates putting letters inside (inserted letters break into the word).
'security code' becomes 'pin' (I can't justify this - if you can you should believe this answer much more).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'pin'+'ie'='pinie'
'k' placed inside 'pinie' is 'PINKIE'.
Can you help me to learn more?
(Other definitions for pinkie that I've seen before include "An American little finger" , "Smallest digit" , "The little finger in America" .)