Need your thoughts on a "how to" situation.

[Mel Bishop]

In the source code forum, I listed a backup program that I've been using for a number of months. Decided to dust off the source and see what I can do to update it.

My current problem is that the archived files are unencrypted. I've been searching for crypto routines and have narrowed the candidates down to two or three possibilities.

Now here's where I need your thoughts: Should I encrypt the files one at a time as they are backed up, encrypt the entire file in one fell swoop or just shell out to a 3rd party encryption program?

Keep in mind that the file(s) are <= 700 meg big.

Also, along this line, how can my program tell if a file is "in use by another process" so it doesn't crash?

[Michael Mattias]

Now here's where I need your thoughts: Should I encrypt the files one at a time as they are backed up, encrypt the entire file in one fell swoop ..

Depends. I assume from context the backup program produces a single archive file (ala MS Backup or WinZip).

If "the password" is permission to unarchive any file in the archive, just encrypt the archive. OTOH, if permission for one does not imply permission for all, encrypt seperately with separate passwords.

Also, along this line, how can my program tell if a file is "in use by another process" so it doesn't crash?

If you can't open it exclusive for I-O (ACCESS READ WRITE LOCK READ WRITE), it's in use. But your program may not care if it's open for read-only, so you can request ACCESS READ WRITE LOCK WRITE to detect that.

[Brian Chirgwin]

Truecrypt?

Now here's where I need your thoughts: Should I encrypt the files one at a time as they are backed up, encrypt the entire file in one fell swoop or just shell out to a 3rd party encryption program?

One possible solution is to use TrueCrypt (www.truecrypt.com).

You could shell to truecrypt, create a truecrypt volume, mount it and copy the files into it and unmount the volume. Command Line Options