From: Martin Minow <minow@apple.com>
Date: Tue, 14 Dec 93 09:43:52 PST
To: wex@media.mit.edu
Subject: Re:  Signing pictures -- how hard, how long?
Message-ID: <9312141743.AA17043@apple.com>
MIME-Version: 1.0
Content-Type: text/plain


If you have System 7 Pro (and an RSA certificate), you can sign any file,
including a picture stored as EPSF or TIFF or whatever by dropping the
file on your signature -- there are no modifications needed to the
application that created the file. An application can sign pieces of
information within a file (such as the content of a dialog, or the
position of an object) by adding a small amount of code that calls
the Digital Signature Manager. File signatures are verified by the
Finder (or by an application), while object signatures are verified
by the application. The developer toolkit has sample code that shows
how to manage digital signatures, including a drawing program with
signed objects and a Think C class library for signed files and objects.

Martin Minow
minow@apple.com
The above does not represent the position of Apple Computer Inc.