Having gone through several introductory posts covering background
material such as
key containers and
methods of key generation,
we are now ready to delve into the actual cryptographic operations
that use symmetric algorithms in detail.
In a prior post, I described the use
of Windows CryptoAPI to compute message digests and message
authentication codes which ensure integrity of messages. We now
move on to the use of symmetric algorithms in cryptography, which can
be used for both message confidentiality and integrity.
Asymmetric algorithms will be covered in future posts. Refer to the
in this series for the difference between the two.
In my prior post, I introduced
several abstractions — Cryptographic Service Providers,
cryptographic contexts and key containers — that are part
of Windows CryptoAPI and promised to look at
cryptographic keys next.
Well, I changed my mind, figuring it might be better to first talk
about simpler operations that do not require the use of keys at all.
This post thus describes the generation of hashes, message digests
and message integrity codes using Windows CryptoAPI and TWAPI.
This is the second in a series of posts on the use of cryptography on Windows.
The previous blog post introduced the
basic concepts related to cryptography. Here we delve into how those
concepts are implemented in Windows at a system or architectural level
and of course, how one accesses them from Tcl. This will lay the
ground for discussing the actual cryptographic operations in future posts.
Security is currently the No. 1 priority for the software industry; and
if that's not the case, it should be, given the current state of
affairs with daily reports of major computer break-ins, credit card fraud,
identity theft etc. It is important for applications, and application
writers, to be aware of these issues and make use of all available
technologies to protect against attacks.
There is no shortage of hotkey programs for Windows, many of them of high
quality. And of course Windows itself allows you to define hotkeys.
However, a hotkey program in Tcl is not only very simple to write,
it offers the full flexibility and power of Tcl
behind it. Meaning what exactly? Read on.
There are times during software development when you want to run
in interactive mode with
maximum privileges on a system, be God as it were. One might think
running as Administrator would do it but it doesn't.
To be truly omnipotent
on Windows, you have to run under the LocalSystem
It is easy enough with Tcl and this post shows you how.
As a side bonus, it also describes how to inject processes into the interactive
user's desktop to run under the user's account as well.
One of the strengths of Tcl
is the ease of integration with other software, whether they
be COM components, libraries or even executable programs that
are not designed for interaction with other programs. Here we look
the facilities Tcl offers related to the last of these --
running external programs and optionally
interacting with them using standard I/O mechanisms.