Nothing in Jean's Southern Appalachian book that could be interpreted as locks and keys. I don't think it would be related to Locks and Bolts Keys as that motif is very strong particularly in early broadside ballads and all of the versions I have seen the word 'bolts' is consistent.

I have seen 'locks and keys' used together as euphemisms, some versions of Chilbridge/Strawberry Fair for instance, but these haven't been found in America.

Could it be a local prison song?