On Jan 5, 2006, at 8:30 AM, Fred Wolfe wrote:
We sometimes loan our set of research stata dta files and programs
we have developed to investigators to work with. We have some
concern that the files could be passed on to others that shouldn't
have access to them or that they might just sit on a computer and
be accessible to other. It occurred to us that one way to protect
files would be to have a pass word and date requirement. For
example, after 6 month the dta files would not be accessible
without a (changing) password (which we would have to supply). I
wonder if anyone else has thought about issues such as these or if
Stata Corp has some plans or ideas on the subject.
In order to share sensitive files with another individual, you must
trust that individual to handle those files properly. This includes
disposing of them securely when he or she is finished using them.
The expiration date you suggest could be easily subverted in a number
of ways (e.g., one could simply read the data into memory and then
save a copy, or alternatively, simply open a log file, list the data,
and then read it back out of the log).
Sharing files via symmetric encryption (i.e., using a common
password) is inherently problematic. First, the password itself must
be shared (and stored) in a secure manner, and this can be difficult
to do. Second, you need to generate a different password each time
you want to share with a different person or set of persons. These
problems are avoided with public key (or asymmetric) encryption. We
use public key encryption extensively to store and distribute data
files securely for several collaborative projects.
Take a look at http://www.gnupg.org/. From there you can download
GnuPG -- a widely used open source program for public key
encryption. To learn more about public key cryptography, you might
try the "Links" page on that site and/or Wikipedia. If you're
instead interested in a commercial solution, see http://www.pgp.com/.
-- Phil
P.S. One drawback with using gpg to encrypt data files is that you
must decrypt them manually each time you want to use them, and then
remember to wipe the decrypted version when you're done. A possible
way to facilitate this would be for -use- to recognize that a file is
encrypted and then call gpg automatically to decrypt it (prompting
the user for his or her passphrase), piping the decrypted stream
directly into Stata (this way, a decrypted version of the file is
never written to disk and thus you don't have to worry about
remembering to delete it). I believe GnuPG can be built on all
platforms supported by Stata. Perhaps I'll raise this as a "wish" at
the next Users Group Meeting.
-- Phil
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