I interpretd Hank's line about the encryption to be the writers telling the audience that the DEA would not have gotten in. Not because it's more realistic, but that there's no other reason to put those words in Hank's mouth besides that they want us to see the irony that Walt's downfall will be caused in the end by his too clever and audacious plans. Why would Hank lack faith in the ability of the DEA to crack the encryption?
As for the cigarette, what would Walt have done if the Roomba had broken the vial, supposedly exposing them both to ricin? Which of course was really salt, but Jesse can't be allowed to know that.