[NEWS] Karen's Power Tools Newsletter

[NEWS] Making Hash

Vorauseilender Gehorsam — Tue, 25 Jan 2005 22:27:47 GMT

Making Hash
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After all that, a lot of programs might have rested on their laurels. But
not the hard-charging Directory Printer! One of its newest tricks is
making hash.

No, the program hasn't taken up cooking with corned beef. These hashes are
what mathematicians call "cryptographic hashes", or sometimes "message
digests".

We've talked about these hashes before. They are the result of complex
mathematical formulas that transform data in a very special way. Feed a
series of 0s and 1s to a "hash algorithms", and produces a short sequence
of its own. This new string of 0s and 1s is called the "hash value" of the
original data.

Now you may be wondering: what's so special about these formulas? After
all, any child can write rules to change data from one form to another.
But hash algorithms have two important features that make them very
unusual, and very valuable.

First, each formula always produces the same number of bits, no matter how
many bits it's asked to process. For example, one popular hash algorithm
is called SHA-1 (Secure Hash Algorithm version 1). Feed it one bit, or a
trillion bits. It always provides 160 bits in return.

Second, the bits produced by hash algorithms are exquisitely sensitive to
the data they process. The tiniest change in the original data produces
huge changes in the end result.

To see this in action, let's use a formula called MD5 (Message Digest
version 5). The hash values it calculates always contain exactly 128 bits.
As an experiment, I fed it two nearly identical streams of data.

The first stream contained exactly eight billion binary 1s. Here's the
hash value it computed:

    1000100011111110 0100100011110010 0110100110111011
    0000010011011011 0100100000010111 0010101001001100
    1111101001001100 1110001010001110

Hmm... That's a little hard to read. Let's try again, this time showing
the result in the (slightly) more human-friendly hexadecimal numbering
system:

    88FE 48F2 69BB 04DB 4817 2A4C FA4C E28E

Not great, but it will have to do.

Next, I asked the formula to process a slightly different block of data.
This time, the input contained "just" 7,999,999,999 1s, followed by a
single 0. In other words, this second test differed from the first by just
one bit - one out of eight billion.

This time the MD5 algorithm calculated this hash value:

    6F87FE5068BF3FA23628152A1FF962BB

See any similarities between the two hashes? I don't either. And that's
the point. Although the two blocks of data fed into the equation differed
by only one bit in eight billion, the results have almost nothing in
common.

Together, these two features make hash values convenient "fingerprints" of
files. If two files contain the same data, their hash values will be
identical too. Likewise, if a file doesn't change over time, its hash
value won't change either.

But make any change in a file's contents - no matter how slight - and the
new data's hash value will change. And even if two files have exactly the
same name, size, attributes, dates, and other characteristics -- if their
hash values differ, their contents do too.

Computer crime investigators use hash values to test and prove the
integrity of evidence. When data is recovered from a suspect's computer, a
hash value of each file is computed. Later, a witness can demonstrate a
file hasn't changed while in police custody, by showing the hash value
computed at the time of the trial exactly matches the one computed when
the data was seized.

Some careful folks compute the hash values of backup files containing
sensitive data. Later, they can verify the archived data's integrity by
re-computing data's hash value. If the new and old values are the same,
the backup data is intact. If not, the data has suffered bit-rot, with at
least one 0 becoming a 1, or vice versa.

Now you and I can use hash values too. Just ask the Directory Printer to
compute and print hash values for all your important files. Later, if you
suspect a file has been altered, ask the Directory Printer to perform the
task again. If the hash reported today matches the original value, the
file is intact. But if the hash values differ, the file's contents have
changed.

Incidentally, there are six hash algorithms in common use today. I've
already mentioned two of them: MD5 which produces hash values containing
128 bits, and SHA-1 which produces hashes that are 160 bits long.

The others are: SHA-224, SHA-256, SHA-384 and SHA-512.  In each case, the
number following the letters "SHA" indicates the length of the hash values
produced by the algorithm, in bits. For example, the SHA-512 formula
yields hash values containing 512 bits (64 bytes).

For most purposes, the shorter hash values serve us just as well as their
longer colleagues. [Nerdy Note: Exceptions include hash values used in
some types of cryptography. There, longer hash values provide greater
security] Shorter hashes are easier to read and compare. But the new
Directory Printer lets you chose which hash values you'd like to see. Now
you can select any, or all, of the six SHA and MD5 variations!

[NEWS] Karen's Power Tools Newsletter

Vorauseilender Gehorsam — Tue, 25 Jan 2005 22:24:28 GMT

KAREN'S POWER TOOLS NEWSLETTER

January 25, 2005

By Karen Kenworthy

Read the Web version of Power Tools online!
http://www.karenware.com/newsletters/2005/2005-01-25.asp

New Directory Printer!
----------------------
While there's still time left in the day, I decided to upgrade one of the
most popular of my Power Tools programs. The project started modestly, but
before long turned into a big job. Along the way I wore out one keyboard,
and ran my poor computer mouse ragged. I refurbished thousands of old
bits, and still needed buckets of new 1s and 0s.

But I think it was worth it. Finally, the new Directory Printer v5.0 is
ready!

Long-time readers will remember the Directory Printer. It began as a small
program that could print lists of files found on our hard disks,
diskettes, and CDs. In addition to each file's name, the program printed
the file's size, and the dates it was created, last modified, and last
accessed.

True to its name, the Directory Printer also printed details about the
folders where our files are stored. Naturally, the number of files and
sub-folders each folder contains were reported. The total size of the
folder's contents could be printed too. Want to know when a folder was
created, last modified, or last accessed? The program could report those
details too.

Contrary to its name, the Directory Printer could also write the
information it uncovers to a text file. These files can be stored in a
safe place, providing an historical record of a drive's contents. They can
also be imported into spreadsheets and databases, letting you analyze,
sort, and compare the information the Directory Printer collects.

Whew! The early Directory Printer did a lot. But like every successful
program, it has never been finished. Over the years the little tool
learned to reveal several "attributes" of files and folders, including:

Read-Only. Files with this attribute can be read, but not changed or
deleted. Files stored in Read-Only folders can be read, but

Hidden. These files and folders are not normally displayed by Windows. In
theory, this provides a certain amount of protection to important files
and folders.

System. This attribute indicates a file or folder is used by Windows.
Should one of them disappear, or be improperly altered, Windows may behave
erratically or not run at all.

Compressed. Files and folders with this attribute have been compressed by
Windows, to save disk space.

Encrypted. This attribute identifies files that have been encrypted by
Windows, at our request. A password is required before any program can
read or modify their contents.

Executable. Files with this attribute are programs, or files containing
program fragments. The data stored within them are computer instructions -
- numbers that order computers to add, subtract, read and write disks,
display cute images, make loud beeping sounds then crash, and do all the
other endearing things that make us love our binary buddies.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

All of Karen's Power Tools
--------------------------
  Note: For the most up-to-date list, visit:
  http://www.karenware.com/powertools.asp

* Directory Printer - http://www.karenware.com/powertools/ptdirprn.asp
  Time Sync - http://www.karenware.com/powertools/ptsync.asp
  Zone Manager - http://www.karenware.com/powertools/ptzone.asp
  Print Logger - http://www.karenware.com/powertools/ptprnlog.asp
  LAN Monitor - http://www.karenware.com/powertools/ptlanmon.asp
  URL Discombobulator - http://www.karenware.com/powertools/ptlookup.asp
  Window Watcher - http://www.karenware.com/powertools/ptwinwatch.asp
  'Net Monitor - http://www.karenware.com/powertools/ptnetmon.asp
  Drive Info - http://www.karenware.com/powertools/ptdinfo.asp
  E-Mailer II - http://www.karenware.com/powertools/ptmailer2.asp
  Countdown Timer II - http://www.karenware.com/powertools/ptcount2.asp
  Computer Profiler - http://www.karenware.com/powertools/ptprofiler.asp
  Replicator - http://www.karenware.com/powertools/ptreplicator.asp
  Disk Slack Checker - http://www.karenware.com/powertools/ptslack.asp
  WhoIs - http://www.karenware.com/powertools/ptwhois.asp
  Recycler - http://www.karenware.com/powertools/ptrecycler.asp
  Show Stopper - http://www.karenware.com/powertools/ptstopper.asp
  Alarm Clock - http://www.karenware.com/powertools/ptalarm.asp
  Font Explorer - http://www.karenware.com/powertools/ptfonts.asp
  Power Toy - http://www.karenware.com/powertools/pttoy.asp
  Time Cop - http://www.karenware.com/powertools/pttimecop.asp
  Hasher - http://www.karenware.com/powertools/pthasher.asp
  Mailer - http://www.karenware.com/powertools/ptmailer.asp
  Version Browser - http://www.karenware.com/powertools/ptbrowse.asp
  Autorun.inf Editor - http://www.karenware.com/powertools/ptautorun.asp
  Cookie Viewer - http://www.karenware.com/powertools/ptcookie.asp
  Registry Pruner - http://www.karenware.com/powertools/ptpruner.asp
  Registry Ripper - http://www.karenware.com/powertools/ptregrip.asp
  Snooper - http://www.karenware.com/powertools/ptsnoop.asp
  Clipboard Viewer - http://www.karenware.com/powertools/ptclpvue.asp

* Indicates program was updated recently.

NOTE: You should use Control Panel's "Add/Remove Programs" applet to
remove the old version, before installing a new version of a Power Tool.

Note: Be sure to install the Visual Basic Runtime v6.0 before installing
your first Power Tool. It's required by all the Power Tools, and must be
installed first. You can download a copy of the Visual Basic Runtime v6.0
installer, vbrun60-setup.exe, from any of the pages where you download the
Power Tools themselves, or from my special Runtimes page at:
http://www.karenware.com/runtimes.asp