I believe, the only way to protect the files from reading,
is to encrypt them, and to protect from tampering,
is to checksum (digitally sign) them.

Checksums must be kept on a physically secure media, like on
a USB stick that you carry with you. USB stick may as well be
encrypted and protected with a passphrase.

Some unices offer encrypted filesystems that can be mounted
only after submitting the passphrase-protected private key.
Theft or illegal copy of such media or even the whole machine
gives the thieves no access to the data.
However, once and as long as mounted, the data can be
read/modified by anyone who has relevant local or remote access
to the machine.

You may want to crosspost to security newsgroups
to get some more detailed answers.

Regards,
Andrei