My question is can I store a private key in a docker?
I mean: is it safe or can it be acessed? is there a way to do?
you could, but it is far away from being safe. also depends against which scenario you want to be safe.
the better solution would be to use docker secrets
I need to send a docker to a PC and be sure that it is executed, so the sent docker send a signed message (at each timeout) (with its key)
but if the owner of the PC is evil and don’t want to execute the docker, if he gets the key he can forge the signed message 
if the evil PC, has your docker image (which sounds so), then the evil person can access every file there; also a private key if it is there.
so docker secrets don’t help?
same stuff if I send a paused container?
damn my thesis is screwed :’(