And you are failing to understand the legal questions at issue...
The Fifth Amendment, as currently interpreted, doesn't provide the protection you describe. It protects against giving self-incriminating testimony and essentially the question is whether the password is "testimony." Keep in mind that the government is not asking him to disclose it, just to type it into the computer. Here's a good discussion: http://volokh.com/posts/chain_1197670606.shtml (There seems to be a CSS problem with that page, but the text is fine.)
The Fifth Amendment, as currently interpreted, doesn't provide the protection you describe. It protects against giving self-incriminating testimony and essentially the question is whether the password is "testimony." Keep in mind that the government is not asking him to disclose it, just to type it into the computer. Here's a good discussion: http://volokh.com/posts/chain_1197670606.shtml (There seems to be a CSS problem with that page, but the text is fine.)