GK-Crypt Data Security Package Version 01
User Manual - March 18, 2006


     GK-Crypt keeps your computer files secret and private.  It keeps them
secure against any snooping, industrial espionage, or intrusion via the
Internet.  Even if your computer or your data disks were stolen, and even
if they had the GK-Crypt software on them, nobody could read your data.

     GK-Crypt is far stronger than any other commercial file encryption
product in the world, and stronger than nearly all of the world's
diplomatic and military encryption packages, whether hardware, software or
any combination.  GK-Crypt is strong enough so that governments could use
it for their most sensitive data.

     GK-Crypt could insure the privacy of your computer files even if an
opponent had available all of the computing power in the entire world.
And, your files will stay private for decades to come.  Even if computers
increased in power over the next 50 years by the same factor that they
improved over the past 50 years, your files would still remain secure.

     The 128-bit encryption products now in use will become obsolete in 10
to 15 years.  The 256-bit products that are designed to replace them will
become obsolete in 20 to 30 years.  But files encrypted with 640-bit
GK-Crypt will still be secure even 50 years from now.

     GK-Crypt is easy to use.  You can encrypt hundreds of files with a
single command.  You don't need to choose and remember any of the file
keys.  GK-Crypt can generate a secure 640-bit key for each file, and
remember all the keys for you.

     GK-Crypt is also the safest privacy product you can buy.  It is loaded
with safety features to prevent loss of data and other problems that are
common with lesser data security packages.  You cannot decrypt a file with
the wrong key, or encrypt a file that is already encrypted.


  1.1. What is encryption?
  1.2. Who needs encryption?

  2.1. A GK-Crypt session
  2.2. The basics
  2.3. Sample session

  3.1. Identifying files
  3.2. File groups and wildcards
  3.3. Group overlap

  4.1. Key Do's and Don'ts
  4.2. Letters, digits and punctuation
  4.3. Key blocks
  4.4. Pronounceable keys
  4.5. Patterns
  4.6. Multiple copies
  4.7. Secretaries and clerks
  4.8. Key strength
  4.9. Summary: Picking a key

  5.1. Copying the GK-Crypt files
  5.2. Multiple copies of GK-Crypt
  5.3. Installation
  5.4. Practice

  6.1. Full automatic mode
  6.2. Generating keys
  6.3. Separate group keys
  6.4. Separate file keys

  7.1. Lost keys
  7.2. Strong Master Key
  7.3. Unauthorized users
  7.4. Double encryption
  7.5. Double copies
  7.6. Partial encryption
  7.7. Master and cache
  7.8. Adding and renaming files
  7.9. Backups and recovery

  8.1. The GK-Crypt algorithm
  8.2. AES Advanced Encryption Standard
  8.3. RSA public key cryptography
  8.4. Quantum cryptography

Appendix A. DOS BASICS
  A.1. Starting DOS
  A.2. Sizing the DOS window
  A.3. Directories
  A.4. Current directory
  A.5. Working with directories
  A.6. Identifying files
  A.7. File operations

1.1. What is encryption?

     Encryption is the process that keeps your data secure.  The GK-Crypt
program takes your data file and transforms it into a form that nobody can
read without the key.  The encrypted file looks perfectly random and
totally meaningless.  Even the most sensitive and sophisticated statistical
tests cannot detect any difference between your encrypted file and a pure
random file.

     The reverse process, which is called decryption, takes the garbled,
unreadable data file and transforms it back into the original data.  The
decryption process requires full knowledge of the key in order to
reconstruct the original data.  Only you, and anyone to whom you give the
key, can retrieve and read the data file.  For an unauthorized person who
does not have the key there is no possibility whatsoever of reversing the
process and reading your file.

     You can think of encryption and decryption as locking and unlocking
your data files.  The key is just like the combination for a safe or vault.
Without the combination the vault cannot be opened.  Without the key your
data file cannot be read.  But, unlike a safe or vault, there is no other
way in.  The snooper cannot cut through the walls or manipulate the
tumblers with magnets.  The key is the only way in.

1.2. Who needs encryption?

     You need encryption whenever you have both of the following

(1) You have data that you need to keep private or confidential, and

(2) Someone has access, or could possibly have access to your computer, or
to any external media where your data is stored, or to any channel over
which you transmit your data.

     Here are some kinds of data that you might want to keep secure.

Private individuals

     Bank account numbers          Financial records
     Book or play manuscripts      Health information
     Brokerage account numbers     Inventions
     Computer passwords            Personal photos
     Credit card numbers           Private letters and emails
     Downloaded files              Spreadsheets


     Ad campaign plans        Merger plans
     Claims data              Orders
     Client records           Organization charts
     Commissions              Patient records
     Compliance data          Product specifications
     Contract terms           Recipes
     Credit histories         Real estate plans
     Customer accounts        Research findings
     Expansion plans          Revenue projections
     Employee health data     Salaries
     Interfaces               Sales records
     Inventory                Settlement records
     Letters and memos        Supplier data
     Mailing lists            Tax information
     Marketing plans          Yields


     Armaments              Resupply schedules
     Attack plans           Ship movements
     Contracts              Supply levels
     Defense plans          Targets
     Emplacements           Trajectories
     Munitions supplies     Troop movements
     Radar frequencies      Troop strength
     Radar locations        Unit readiness
     Research reports       Weapons capabilities

     For some types of data, you may have a legal obligation to safeguard
its privacy.  For example, the Gram-Leach-Bliley Act (GLBA) which Congress
passed in November 1999 requires that companies protect the security and
confidentiality of their customers' private information.  Financial
institutions and other businesses must assure that their customers' data is
kept private and confidential.

     Similarly, since April 2005, nearly all healthcare institutions need
to comply with the security requirements of the Health Insurance
Portability and Accountability Act (HIPAA).

     If you take your legal obligations seriously, then you should use the
strongest encryption product available, the GK-Crypt package.

     Your data could be vulnerable because clients, or unauthorized
employees, may be able to enter an area where your computer is located, or
where another computer or terminal on the same local network is located.
Sometimes a careless employee or family member may leave a computer
unattended where someone might use it to find sensitive files.

     Sometimes a disgruntled employee, or even an angry family member, may
copy data files in order to harm you or your company, or to sell the data
for profit.  The employee could make a disk or print out a file and take it
home.  An employee who works from home, or someone else in that household,
may be able to dial into your computer and obtain access to sensitive

     Access to your data might be gained while your computer is connected
to the Internet by using spyware or a computer virus.  Files transmitted on
the Internet are not secure at all.

     It is also possible that a computer or data disks or tapes will be
stolen, or obtained from the trash.  A thief who breaks into a safe looking
for valuables may take backup disks containing your sensitive data and
later discover what they contain.


     Each time you use GK-Crypt is called a session.  During each session
you can encrypt files (lock them to make them secure), decrypt files
(unlock them to use them), or get a list of the encrypted files.  You may
encrypt or decrypt as many files as you like during each session.  You can
even encrypt and decrypt the same files in a session, should you wish.

     You start each session by typing the GK command.  This starts the
GK-Crypt program.  You start a session by typing


and pressing Enter.  After GK-Crypt is started it will tell you exactly
what to do at every step.  Everything is clearly explained as you go.  (But
you should still read this manual and the Installation Guide before you

2.1. A GK-Crypt session

     The first thing GK-Crypt will need is your Master Key.  This is the
key that opens the Master File which is required to run the GK-Crypt Data
Security Package.  It is absolutely essential that you choose a Master Key
that is very strong.  If the Master Key is weak, or only moderately strong,
then your security will be compromised.

     Using an ultra-strong encryption algorithm like GK-Crypt and then
choosing a short or weak key is like building a bank vault from the
strongest thickest steel available, and then locking it with a dime-store
lock.  Several sections of this manual will be devoted to choosing keys
that are both strong and easy to remember.

2.2. The basics

     There are three basic things that you need to consider when you use
the GK-Crypt security package:  files, keys, and options.  Files contain
the data that you want to protect.  Keys are secret passwords that you use
to protect your files.  Options are all of the different ways that the
GK-Crypt package can be used to protect your data files.

     The next three chapters will discuss these three subjects in greater
detail.  If you are new to DOS, it might be a good idea to read the
Appendix on DOS Basics before reading the chapter on Files.

2.3. Sample session

     Before getting into the full details of a session, let's take a quick
look at a sample session.  You start GK-Crypt by typing the command


The first thing GK-Crypt needs is your Master Key.  GK-Crypt will prompt
you to enter the Master Key by displaying

     Please enter the Master Key

You type your Master Key exactly the way you entered it when you installed
GK-Crypt, for example,

     Key: KXWVT 39463 HMCTU 90413 GSVIF 85721

Remember that the Master Key is case-sensitive, so KXWVT and kxwvt are
completely different keys.  If the Master Key is correct, the session can

     GK-Crypt will next need to know which files you want to encrypt (lock)
or decrypt (unlock).  It will first ask what operation you want to perform,
like this,

     Do you wish to
       E - Encrypt a file.  Make it unreadable to protect it.
       D - Decrypt a file.  Make it readable to use it.
       L - List the encrypted files.
       Q - Quit.
     Type your choice (E, D, L or Q):

You may encrypt and decrypt as many files as you wish during a session.
After each operation you will be returned to this menu until you type Q to

     Suppose that you want to encrypt a file.  You type E to select
encryption.  GK-Crypt will then need to know the name of the file, or the
group of files that you want to encrypt.  It will prompt you for the name,

     Enter the name of the file group to be encrypted,
     or type Q to quit.
     File group name:

Suppose that you want to encrypt the group of files in the directory
newinvention that start with the name motor.  You could respond

     File group name: \newinvention\motor*

GK-Crypt will ask you to verify your choice, so that you don't accidentally
encrypt the wrong group of files.  It will ask

     Is (\newinvention\motor*) the correct file group? (Y or N):

You would type Y to indicate that it is correct.  If you chose to select
your own keys, then GK-Crypt will prompt you to enter the key, otherwise
GK-Crypt will select the key and encrypt the file immediately.

     This sample should give you a good sense of how a GK-Crypt session
will proceed.  At every step GK-Crypt will instruct you on what information
you need to enter.  Now let's look at some of these items in detail.


     In order to use GK-Crypt you will need to tell it which files to
protect.  On your computer the files are organized into directories or
folders.  Directories and folders are two names for the same thing.  When
you are in Windows, the computer will show you lists of files organized as
folders.  When you are in DOS, the computer will show you lists of those
same files in directories.  Directories and folders are equivalent.

     You need to identify which files contain your private data.  These are
the files that you need to encrypt.  Often these files will be in
directories that are named for the program that created them.  For example,
if you create drawings using a program called EZ-Draw, then the drawings
are likely to be in a directory with a name such as


or in a subdirectory of these directories, say


     It is generally safe, but not necessary, to encrypt the application
program and the files that it uses along with the files you created.  For
example, it is safe to encrypt word processors, spreadsheet programs, or
graphics programs.  Of course you must decrypt them before you try to use
them.  This may take some time, but it may be easier for you to encrypt the
entire directory, along with all of its subdirectories, than for you to try
to identify all of your data files individually.

     WARNING!!  You must never encrypt a system file.  You must never
encrypt any file that is part of the operating system on your computer,
such as Windows, Unix or Linux.  If you encrypt a system file, your
computer will be unable to use that file, and therefore may not be able to
function correctly.  If you simply went ahead and encrypted every file,
your computer would stop running, and you would not be able to restart or
reboot it, so you would not be able to fix the problem.  Similarly, if you
encrypted any of the GK-Crypt files, such as GK.EXE, GKMASTER.1, or
GKCACHE.1, then you would not be able to use the GK-Crypt package to
decrypt them, so all of your encrypted files would be permanently lost.

     You should always give your data files and folders names that clearly
identify what they contain.  That way, you will know which files are yours,
and which files you want to protect.  You can find all of the files on your
computer by clicking the "My Computer" icon on the Windows desktop.
Equivalently, you can find all of your files by using the DIR command in

3.1. Identifying files

     Each time you encrypt or decrypt files you must identify those files
to GK-Crypt.  GK-Crypt will prompt you for the file identifier at the
appropriate time.  You identify files to GK-Crypt the same way that you
identify files to DOS, namely by specifying the drive, path, filename and
extension.  (If you already know DOS, you can skip or just skim this

     drive     is the device where your file is stored, usually
               C for your hard drive, A or B for a floppy drive,
               D or E for a CDROM drive.

     path      is the directory on your drive where the file is

     filename  is the name that you gave your file.  The name
               usually indicates the contents or purpose of the

     extension is a suffix that indicates the kind of file, such
               as TXT for a text file, JPEG for a picture file,
               EXE for an executable file, etc.

A full file identifier might look like this,


     In this example, c: identifies that your file is on the C drive, which
is your hard drive.  \mycompany\mydepartment\2005\ is the path to your
data.  It shows that the data file is located in the 2005 folder, which is
inside the mydepartment folder, in the mycompany folder.  So the path
consists of nested folders, or a list of directories.  sales.wp is the file
with the data.  The filename is sales, and the extension is wp, which
indicates that it is a WordPerfect document.

     In a file identifier all of the fields except the filename are

     drive      can be omitted if the file is on the current
                drive, that is, the drive where you are now

     path       can be omitted if the file is on the current
                directory of the drive.

     extension  can be omitted if the file does not have an
                extension on its name.  For example, if the file
                is just named oldstuff then no extension is

Here are some examples of valid file identifiers:

          identifies the file budget in the current directory
          of the A drive.

          identifies the file commissions in the \jones directory
          on the current drive.

          identifies the file requests.txt in the late
          subdirectory of the current directory.

3.2. File groups and wildcards

     GK-Crypt allows you to encrypt or decrypt groups of files with a
single command.  There are two ways to do this.  The first method is to use
wildcards when you give the filename or the extension.  Instead of giving
the entire filename or extension, you give the first few characters, and
then type * asterisk.  The file operation will be applied to all files
whose names or extensions begin with the letters you gave.  Here are some

     TAX*        specifies any file in the current directory
                 whose name begins with TAX.  For instance this
                 would include TAX, TAXES and TAX2005 but not

     T\*.DOC     specifies any file in the T subdirectory of the
                 current directory, whose extension is DOC.  For
                 instance this would include T\SALES.DOC and

     \A\PR*.S*   specifies any file in the A directory of the
                 current drive whose filename starts with PR and
                 whose extension starts with S.  For instance
                 this would include \A\PROFIT.S and \A\PRICE.SET.

     The second method for specifying a group of files is to give the path
with no filename or extension.  In this case, the file operation will be
applied to all of the files in the current directory, and all of its
subdirectories.  For example

     \MENU\   specifies all of the files in the MENU directory of
              the current drive, and all of its subdirectories.
              For instance it would include \MENU\TODAY.TXT,

     Any time you are prompted to give a file group you may give either a
single file, a set of files using wildcards, or a directory.

3.3. Group overlap

     It would be dangerous to encrypt two groups of files that could
potentially overlap.  For example, if you were to encrypt the group TOP*.D*
and then encrypt the group TO*.DOC the file TOPIC.DOC would get encrypted
twice.  If you then decrypted those two groups in the same order, the file
TOPIC.DOC could get hopelessly garbled.  It probably could never be

     To prevent this sort of catastrophe, GK-Crypt detects possible
overlaps of file groups, and prevents you from encrypting such overlapping
groups.  This is one of the many safety features built into GK-Crypt.


     Choosing the keys for encrypting your files is one of the most
critical steps in using the GK-Crypt package.  If you choose a short or
weak key, it may be easy to remember and easy to type each time you need
it, but your data will not be secure.  It is a serious mistake to think
that you can use a weak key simply because you are using such a strong
encryption package.  A strong safe with a weak lock is not secure.

     If you choose a long strong key your data will be more secure, but it
will be harder for you to remember it and to type it accurately each time
it is needed.  This chapter will describe techniques for choosing keys that
are both secure and easy to remember and to type accurately.

4.1. Key Do's and Don'ts

     Many people try to take shortcuts in order to have keys that are easy
for them to remember.  You need to assume that any opponent will also be
aware of the same shortcuts.  Here are some simple rules that can help
prevent a costly error.

     When you choose a key, do not base the key on your personal
information.  Assume that your opponent knows all of your personal data.

DO NOT base your key on

     Your birthday
     Your telephone number
     Your Social Security number
     Your license plate number
     Your spouse's, child's, parent's, sibling's or even
       your pet's name, birthday, phone number, etc.

DO NOT base your key on commonplace phrases

     Nursery rhymes
     Song titles or lyrics
     Folk sayings
     Names of famous people, groups, places or events
     Names of books, plays or TV shows
     Punchlines from jokes
     Well-known dates
     Tongue twisters
     Words or phrases in other languages

DO NOT use data widely known within your specialized field

     Digits of pi or e
     Names of bones, nerves, or organs
     Names of stars, minerals, geological features, bacteria,
       ancient cultures, alloys, proteins, theorems, etc.
     Names of people, schools, companies, places, etc.
     The speed of light, Avogadro's number, the Golden Ratio, etc.

DO NOT choose sequences of consecutive letters from the alphabet or from
the keyboard, whether forwards, backwards or diagonally.

DO NOT use the keys that appear in this manual.  Always assume that your
opponent has read it, too.

DO use a long key.

DO try to make your key as random as possible.

DO read this entire chapter on picking keys.

DO evaluate the strength of your key according to the principles in the
following sections.

DO make your Master Key extra long and strong.

4.2. Letters, digits and punctuation

     If there are several people who need access to the data, and who are
trusted with the keys, then the problem of recording or memorizing the keys
becomes multiplied.  Some people have the capacity to memorize long strings
of random-looking letters and/or digits, but most people cannot do this.
The safest course is to write down your key, and keep it in a secure place,
such as a locked safe.  Other techniques will be discussed in a later
section.  It is advisable to have several copies, in case one copy gets
lost, stolen or destroyed.

     The strength of an encryption key is measured in bits, the binary
digits that are used by your computer's hardware.  Here is a rough guide to
how many bits you get from each character in an encryption key when the
characters are chosen randomly.

     Table 1.  Strength of each character in a key.

     Decimal digit = 3.3 bits
     Single case letter = 4.7 bits
     Mixed case letter = 5.7 bits
     Mixed letter or digit = 5.9 bits
     Mixed letter, digit or punctuation = 6.3 bits

Based on this chart, here is the strength of some sample 10-character keys

     Table 2.  Strength of 10-character blocks.

     5835701483 = 33 bits   Decimal digits
     CIWMRPTNZX = 47 bits   Upper case letters
     tyuhbivxks = 47 bits   Lower case letters
     DmbHaqREkV = 57 bits   Mixed case letters
     ku8Je94Lg7 = 59 bits   Mixed letters and digits
     g"p5WZc4%F = 63 bits   Mixed letters, digits, punctuation

     As you can see, the strength of the key increases when you choose
randomly from a larger set of characters.  However, the difficulty of
memorizing the keys and typing them accurately becomes much greater as the
keys get more random.

     Note that all of the keys illustrated above are too short to be
considered secure.

4.3. Key blocks

     There are several methods for producing keys that are secure, yet
easier for people to manage.  The first technique is to break your keys
into blocks.  It has been a common practice for many years to break coded
messages into blocks of 5 characters each so that they can be transcribed
more accurately.  The same idea works for keys, too.  Notice how the key


becomes much easier to read when it is broken into groups of 5


     For longer keys it may be advisable to use additional punctuation to
organize the blocks into groups of blocks.  For example,

     48591-04528-16392, 35207-31654-74925, 09482-71653-42570


     The second technique is to use groups that have the same structure.
Here are some examples, and the strength of each key block

     91486 61872 94373   16 bits per block   5 digits
     T3708 D6204 F5193   18 bits per block   1 letter, 4 digits
     GS437 BR092 LX528   19 bits per block   2 letters, 3 digits
     UHM15 XTN63 MYA74   21 bits per block   3 letters, 2 digits
     QRILC PJRMS OVDZK   23 bits per block   5 letters

The strength remains the same when the letters are placed in different
positions.  For example, all of the following keys have the same strength,
namely 2 letters and 3 digits

     GS437 BR092 LX528   Letters at the start of each block
     943KP 471GQ 205YL   Letters at the end of each block
     V107J X219C F738L   Letters at both ends of each block
     6WF52 9TU48 7JN13   Letters in the middle of each block

     One advantage of using key blocks that always have the same structure
is that there is no confusion between letters and digits.  Some letters and
digits that may get confused are

     Letters   B G I l O S T Z
     Digits    8 6 1 1 0 5 7 2

Its position in the block tells you whether the character is a letter or a
digit, so there is no need to avoid these characters when you use blocks
with a fixed structure.

     Another variation on this idea is to make each key block uniform, but
to vary the types of blocks randomly.  Here are two 30-character keys with
uniform blocks.  Each block consists of all digits, or all uppercase
letters, or all lowercase letters.

     KNUHW 50258 fewrz 39274 gyakf obqnk

     doztc 81463 69917 AGNDL rdefo PUIZH

4.4. Pronounceable keys

     Another technique that can be used to produce keys which are secure,
yet easy to remember, is to make the keys pronounceable.  That is, you
would use pronounceable combinations of vowels and consonants to form
syllables, and combine these syllables to form artificial words.  This
method may be valuable in situations where it is unsafe to write down the
keys, and they must be memorized.  Here are some examples.

     shambu dilp prelec oltu domex sarbuti shum obior

     Yotz doruc flean jadmek pra kerazi, Lagatu limbrazon.

     You can burn the key into your memory by starting with just a few
pseudo-words, say DOZEK ULM HAPLICO, and repeat these to yourself for a day
or two.  Then add another few words, say DOZEK ULM HAPLICO GRUX ANTIAM, and
repeat those in your head for a few more days.  You can add some more words
the following day.

     dozek ulm haplico grux antiam ludovesk gur amesqi

     You can complete the process by adding capitalization and punctuation,

     Dozek ulm Haplico "grux Antiam" ludo-vesk gur a'mesqi.

Using mixed-case letters and punctuation greatly improves the strength of
your key.

     You can imagine the key to be a saying in some private language, and
make up a translation, in order to fix it more firmly in your mind.  For

     Old king Haplico "lord of Antioch" out-witted a sorcerer.

     In a pronounceable key each letter has a strength of about 3.3 bits if
the words are fairly uniform in length, and about 3.5 bits if the words are
more variable in length.  For example, the first key below is fairly
uniform in length, while the second is more variable.

     panek dilbap greho drung fasdop ulben bukty cruvan

     lobykar elb dixiat glem urbiqeo dhorsh um vilagump

4.5. Patterns

     When choosing a key, avoid creating any patterns, such as repeated
letters or syllables.  Patterns weaken the keys by making them easier to
guess.  Here are some examples of keys with patterns.

     BBXXTT KKUUVV WWYYCC      The letters are all in pairs.
     aaa3gg5yyyy9ccc7uu2       There are runs of equal letters.
     10704 20906 50803         The second and fourth digit in
                               each group is zero.
     51615 38183 29092         Each group has an ABCBA pattern.
     zampana reveske flogoto   The vowels in each group are all
                               the same.
     tuntam memescu saksoli    The first and second syllable
                               start with the same letter.
     debendik devogi delakt    Every group starts with de.
     ABC ghi LMN def XYZ       Each group has 3 consecutive
                               letters of the alphabet.
     500XD 711TJ 822GN         The second and third digits in
                               each group are the same.
     31734 23839 30376         Every group has two 3's.
     dobaku levoti wafigo      Consonants and vowels alternate.
     vgy7 2wdc zse4 7ujm       Has diagonal runs on the keyboard.
     KAZ VEK CIF ZOP HUQ       The vowels run in order AEIOU.

     Once you have chosen a key, inspect it for patterns, and change it to
remove them.  If your key is a long string of letters or digits, look to
see if there are any letters or digits that are used too often, or that are
missing.  You may want to make some changes.  However, don't overdo it.  If
you use every letter or every digit exactly the same number of times, or if
all the letters and digits in each block of your keys are always different,
those are also patterns which weaken the key.

4.6. Multiple copies

     If you have several copies of GK-Crypt on your computer it is safer if
they do not all have the same Master Key.  You need to decide whether these
Master Keys will be completely different, or whether they will differ only

     If you are the only person with the Master Key, or if the same people
will be authorized to have access to all of the files, then it is not
necessary for the Master Keys to be completely different.  It is sufficient
for them to differ just slightly, such as


     On the other hand, if there are some people authorized for certain
files, and different people authorized for other files, then you need to
have completely different Master Keys for each set of files.

4.7. Secretaries and clerks

     Sometimes lower-echelon employees will not safeguard file keys as
zealously as other workers.  It is common for these employees to write down
keys in places that are easily accessible, such as on the computer itself,
on their desk pads or wall calendars, or on slips of paper on a bulletin
board.  Anybody could see the keys and write them down.  It is absurd for
the company president to keep the Master Key in a locked box inside a
walk-in vault, and for the secretary's assistant to write the Master Key on
a gummed label on the wall next to the computer.

     The employee might assume that nobody will ever guess that those
cryptic letters and digits are actually the Master Key that unlocks all of
the company's secret files.  The employee might assume incorrectly.  If
these employees must be trusted with the keys then it is essential that
they be educated to avoid such security breaches.

     If the key is too difficult to memorize, if it must be written down,
and if it cannot be kept locked in a safe, then one possible course is to
hide it in a volume of papers all the same size and color, among many
similar folders.  For example, a key like

     H098V216L B491W635T K307G488X A293R864N

could be hidden in an accounting sheet like

     Foreign currency transactions 3/4/99

     K307G488X  6,025 guilders to sterling
     B491W635T  24,550 francs to dollars
     H098V216L  16,806 dollars to yen
     A293R864N  86,344 dinars to deutschmarks

     Notice that we do not simply read straight down the column.  In this
example, we started at the third line, read upwards to the first line, and
then resumed with the fourth line.  That is, the lines on the sheet were
used in the order 3214 to form the key.  It is even better to skip lines,
and have several dummy lines that are not part of the key.

     Of course your sheet should resemble the papers in your files.  If
your records have lots of pages pertaining to how much commission each
salesperson received, or how many pounds of butterfat each cow produced, or
when each vehicle needed maintenance, then make your key sheet resemble
those.  By the way, there is no rule that your key needs to be on one
sheet.  If you put half the groups on one page, and half on a second page,
that could be even safer.

     A key sheet should never be left lying about, but should be returned
to its file and drawer immediately after use.  It should be filed
appropriately among many similar papers according to its date or filing
number, and not simply placed at the front or back of its folder.
Similarly, the folder should be among others of the same size and color,
and not kept in the first or last position in the drawer.

     Even then, repeated handling will make the paper stand out from others
in the same folder.  Be sure to replace the paper as soon as it starts to
look different, and to shred or burn the old copy.  It is a good idea to
have a decoy paper that looks different placed in a more prominent folder
in a more accessible drawer.

4.8. Key strength

     The following table is a guide to how long a key must be in order to
achieve various levels of security.  For example, if you want a key
strength of 200 bits, and you use a decimal key, then you need 60 digits.
With the speed of current computers 100 bits is the lowest level of
security that can be considered safe.

     The table assumes that the letters or digits of the key are chosen
completely randomly.  If the letters or digits follow some pattern then
your key needs to be longer.  For example, a key such as

     TC174 JF296 BH583 KD629

would be measured as 8 single case letters and 12 digits, for a strength of
77 bits.  It would not be considered to be 20 mixed letters and digits,
which would have a strength of 118 bits.

Table 3.  For each type of key, this table shows how long to make
          the key in order to achieve the desired strength.

                             Key strength measured in bits
Type of key             100   125   150   200   250   300   400
Decimal digits           30    38    45    60    75    90   120
Single-case letters      21    27    32    43    53    64    85
Mixed-case letters       18    22    26    35    44    53    70
S-C letters + digits     19    24    29    39    48    58    77
M-C letters + digits     17    21    25    34    42    50    67
Letters, digits, punc    16    20    24    32    40    47    63
Uniform blocks           22    27    33    44    55    66    88
Pronounceable, uniform   30    38    45    60    75    90   120
Pronounceable, variable  29    36    43    57    71    86   114

For example, if you wanted a decimal key with a strength of 125 bits, you
would need 38 decimal digits.  If you wanted a key of mixed-case letters
and digits with a strength of 250 bits, you would need 42 letters and

     Note that the longest input line you can enter is 126 characters.
(This is a limitation of DOS, not a limit set by GK-Crypt.)  So if you
wanted 400 bits of strength, and you chose to have a decimal key which
requires 120 digits, then you would have only 6 characters left to separate
the blocks.  Your blocks would need to average over 17 characters each.  (A
pattern of 17, 17, 17, 17, 17, 17, 18 would fit.)

4.9. Summary: Picking a key

The best way to pick a key is to follow these steps.

(1) Decide how strong you want your key to be, say 200 bits.
(2) Choose the type of key, say blocks of letters and digits.
(3) Use the tables above to determine the key length.
(4) Randomly choose a key of the required length.
(5) Inspect the key for patterns.
(6) Adjust the key to remove or reduce the patterns.
(7) If you will need the key again, write down the key and keep
        a copy in a secure place.
(8) Type the key when GK-Crypt asks for it.


     The key to using GK-Crypt effectively is planning.  Before you install
GK-Crypt on your computer, you should determine which files you need to
protect.  The list of sensitive data in the first chapter can provide a
starting point.

5.1. Copying the GK-Crypt files

     The first step in installing GK-Crypt is to copy the GK-Crypt files
from the distribution disk onto your computer's hard disk.  Suppose that
you have inserted the distribution disk into the d drive on your computer,
and that you want to install GK-Crypt in a directory called GK on your c
drive.  You would copy the files by issuing the command

     copy d:* c:\gk\

This is a good way to get started.  After you have been using GK-Crypt for
a while, you may wish to install additional copies on your computer so that
you have less typing of file names.

5.2. Multiple copies of GK-Crypt

     Installing multiple copies of GK-Crypt can reduce the amount of typing
you must do.  Suppose that one of the files you wish to protect is

     \Documents and Settings\WordPerfect\SalesReports\July2005

If you installed GK-Crypt in the root directory, or in a GK directory, then
each time you wanted to encrypt or decrypt that document you would need to

     \Documents and Settings\WordPerfect\SalesReports\July2005

On the other hand, if you install a copy of GK-Crypt in the directory

     \Documents and Settings\WordPerfect\SalesReports\

and you make that directory the current directory, then all you would need
to type is


To reduce your typing, and the chance of mistyping file names, you could
install GK-Crypt in the directory, or directories, where your sensitive
data is located.

     You may have as many copies of GK-Crypt as you wish on your computer.
For example, if you needed to protect the files

     \Documents and Settings\WordPerfect\SalesReports\July2005
     \Documents and Settings\WordPerfect\SalesReports\August2005

you might choose to have extra copies of GK-Crypt at

     \Documents and Settings\WordPerfect\SalesReports\

When you copy the GK-Crypt files from the distribution disk, you could
issue the following commands to copy the files

     copy d:* c:\Documents and Settings\WordPerfect\SalesReports\
     copy d:* c:\MyCompany\ExpansionPlan\

Alternatively, you might want to have all of the GK-Crypt files in the
first directory, but only the executable program GK.EXE in the second
directory.  Then you could use

     copy d:* c:\Documents and Settings\WordPerfect\SalesReports\
     copy d:gk.exe c:\MyCompany\ExpansionPlan\

     We suggest that you start with a single copy of GK-Crypt in its own
directory, and add additional copies later, after you have used the program
for some time.

5.3. Installation

     The first time you run GK-Crypt the program will install itself.  You
run GK-Crypt by typing the command


and pressing Enter.  During the installation you will choose your Master
Key and some permanent program options.  You need to choose the Master Key
and the program options carefully because you cannot change them later.

     The first thing GK-Crypt will need is the installation password.  You
will find this enclosed with the GK-Crypt installation disk.  The password
is not case-sensitive.  You can type it in either upper or lower case.

     After you have entered the password, you will be asked to accept the
GK-Crypt Software License.  GK-Crypt can be used only under the terms of
the Software License.

     The next installation step is to choose your Master Key.  It is
essential that you choose a long and strong Master Key.  The types of
passwords that are used for logging onto websites are not nearly strong
enough to provide any real data security.  See the Keys chapter of this
manual to learn how to choose a suitable Master Key.  Be certain that you
write down your Master Key and keep several copies in secure places, such
as locked in a safe, and off-site in a bank safe deposit box.

     After setting the Master Key, you must select some permanent security
options.  The first option that you must choose is

     Do you want the program to choose the options for you?

If you answer Yes, then you are all set.  The program will choose the
options that provide the highest level of security, and you will have no
further decisions to make.

     If you decide to choose your own options, then you will be asked

     Do you want the program to generate the keys for you?
     Do you want a separate key for every file group?
     Do you want a separate key for every file in a group?

In each case, answering Yes gives the highest level of security.

     If you decide to choose your own file keys, then you will be prompted
to enter the file keys at the appropriate times.  See the Key chapter for
advice on selecting a strong key.  You do not have to remember or record
these file keys.  The only key that you must remember is the Master Key.
All other keys are recorded for you by GK-Crypt.

5.4. Practice

     Before you use GK-Crypt on valuable data, it's a good idea to make
some practice runs.  Create a few small files and encrypt them.  Take a
look at the encrypted files.  Then decrypt the files and look at them
again.  Verify that the files are back to their original contents.

     It looks miraculous.  The encrypted files are complete chaos, total
gibberish.  But GK-Crypt restores them to their original form.

     Try encrypting a group of files starting with the same letters, such
as GKTEST1, GKTEST2 and GKTEST3.  Encrypt and decrypt the group as GKTEST*.
Try creating a directory and a subdirectory, such as \GKSAMPLE and
\GKSAMPLE\SUB.  Put some test files in both directories.  Then encrypt and
decrypt the whole group of files as \GKSAMPLE\.

     You might also want to try a few mistakes, just to see what happens.
Try typing your Master Key incorrectly.  Try decrypting a file that is not
encrypted.  Try encrypting a file that does not exist, or that is already
encrypted.  You will see that GK-Crypt protects you against these types of

     Once you have gotten the hang of it, you are ready to try encrypting
some real files.  For your own peace of mind, you should back up the files

     After you have been using GK-Crypt for a while, and you have gained
confidence in your ability to use it correctly, you may want to take all of
your old backups, the ones where the data files are not encrypted, and
destroy them.  Don't just toss them away.  Cut the tapes into shreds.  Chop
the disks into shards.  Don't discard all of the bits in the same place.

     From this point on, all of your backups will contain your sensitive
files only in encrypted form, along with the corresponding GK-Crypt Master
File and cache.


     The first time that you run GK-Crypt it will install itself.  During
the installation you will need to select several options that determine how
file keys will be generated.  You need to choose the GK-Crypt installation
options carefully, because they are designed to be permanent.  Once you
have chosen the options at installation the only way to change them is to
decrypt all of your data files and then delete the Master File.  The next
time you run GK-Crypt it will install itself again.

     We recommend that you use the full automatic mode, because that
provides the highest level of security.  However, there are valid reasons
for choosing some of the other options.  The following sections will
discuss some of the trade-offs.

6.1. Full automatic mode

     The first option you choose during installation is full automatic
mode.  The program will prompt you with the question

     Do you want GK-Crypt to run fully automatically?

If you want fully automatic operation, then you should type Y for Yes.  In
fully automatic mode GK-Crypt will generate all of the file keys for you.
You never need to type or to remember any of the file keys.  GK-Crypt will
generate a different key for each group of files, and for each file within
a group.

     If you choose fully automatic mode, then there are no more options for
you to select, and you can skip the rest of this chapter.  If you decline,
then the next 3 sections will describe the other options.

6.2. Generating keys

     You need to decide whether you want GK-Crypt to generate keys
automatically, or you would prefer to choose your own group keys.  If you
decide to generate your own, then you will need to type your key each time
you encrypt a group of files.  Since you will want to use long strong keys,
this can be quite tedious.  The keys that GK-Crypt generates are stronger
than any keys you can devise yourself.  However, you may prefer to exercise
greater control over the encryption, and therefore wish to use your own
keys.  The program will prompt you

     Do you want the program to generate file group keys

You would respond by typing Y for Yes or N for No.

     The reason that the keys that GK-Crypt generates are stronger than
keys that the user types is because GK-Crypt uses a larger character set.
Even if the user utilized all of the upper and lower case letters, digits
and punctuation on the keyboard, that is still fewer than 100 available
characters.  When GK-Crypt generates a key, it uses all of the 256 possible
character codes.

     The keys that GK-Crypt generates have a strength of 640 bits.  Keys
selected by users typically have a strength of 100 to 150 bits.  Stronger
keys tend to be unwieldy, hard to type, and almost impossible to memorize.

6.3. Separate group keys

     You must decide whether each file group should have its own separate
group key, or whether one key should be used for all groups.  It is much
more secure for every group and every file to have its own individual key.
However, if you frequently need to move files from one group to another,
and want to be able to move the files while they are encrypted, then you
might want to use a single key for all groups.

     A file could move from one group to another because it was copied from
one directory to another, or simply because it was renamed.  For example,
if you had encrypted two groups of files, PR*.* and SH*.*, and then you
renamed the file PRAWN.DOC to SHRIMP.DOC the file would move from the first
group to the second group.  The file has not physically moved on the disk,
but it is no longer part of the PR*.* group, it is now in the SH*.* group
because its name has changed.

     The only safe way to move a file from one encrypted group to another
encrypted group is to decrypt both groups, move the file, and then encrypt
the two groups again.  If you do not want to spend the time to do this,
then you should choose the option to use a single key for all groups.
GK-Crypt will ask you

     Do you want a separate key for each group of files?

You type Y for Yes, or N for No.

6.4. Separate file keys

     You also must decide whether each file within a group should get its
own individual key.  You get the greatest degree of security by having a
separate key for each file.  However, if you need to rename encrypted files
frequently, then it may be worthwhile to use the same key for all files.

     The only safe way to rename a file in an encrypted group of files is
to decrypt the group, rename the file, and encrypt the files again.  If you
do this often, then you might not want to take the time to repeat these
steps every time.  You might prefer to use a single key for every file in a
group.  GK-Crypt will ask

     In each group of files, do you want each file to have a
     different key?

You would type Y for Yes, or N for No.


     The GK-Crypt data security package is designed with safeguards against
all of the common problems that plague other data encryption programs.  It
is therefore the safest, as well as the strongest, data encryption package
you can get.

7.1. Lost keys

     The most frequent problem with encryption occurs when the user forgets
or loses a file key.  The GK-Crypt package has two safeguards against this
problem.  The first safety feature is the cache.  GK-Crypt records all of
the file keys in the cache.  You never need to remember or record any of
your file keys in order to decrypt your data.  The only key you need to
record and remember is your Master Key.  GK-Crypt remembers all of the
other file keys for you.

     The second feature that safeguards against loss of keys is GK-Crypt's
automatic key generation.  GK-Crypt can generate all of your file keys for
you, so you never have to remember file keys, or type file keys, or even
see any file keys.  GK-Crypt takes care of all that work for you.

7.2. Strong Master Key

     Some other encryption packages generate all of the keys, not just the
file keys, but the Master Key and the cache key, too.  The user does not
have to remember any keys at all.

     This is convenient, but it is not safe at all.  Anyone who gets access
to your computer can use the program to decrypt your files.  Anyone who
gets one of your data disks can buy a copy of that program and read your

     Other packages use strong file keys, but require only a simple
password to operate the program.  This means that anyone who can guess the
password can read your files.  It is possible to use a program to generate
and try millions of passwords per second, so it is fairly easy for somebody
to get at your data.

     GK-Crypt lets you use strong Master Keys, up to 126 characters long.
If you follow the guidelines in the chapter on choosing keys, then nobody
can guess your Master Key, not with all the computing power on earth.

7.3. Unauthorized users

     Suppose that a malicious person obtained access to your computer, and
tried to disrupt your business by encrypting some of your files with an
unknown key.  That person might try to ransom your data, and ask for a
large fee to supply the key to recover your data.

     The cache protects you.  The cache records the key, so you can recover
the data even under those difficult circumstances.

7.4. Double encryption

     Another large source of problems with other data security packages is
double encryption, or double decryption.  This happens when the user
forgets whether a file is encrypted or not.  The user might encrypt a file
that has already been encrypted, or decrypt a file that has not been
encrypted, or that has already been decrypted.

     Suppose that the user of some lesser security package encrypts a file
with key 1, and then encrypts it again with key 2.  After the user decrypts
the file with key 2, the file is still encrypted with key 1, and therefore
unreadable.  If the user does not figure this out, and decrypt with key 1,
then the data is lost.

     Now, suppose that the user of this other program has encrypted the
file with key 1 and again with key 2.  Suppose that the user did this
intentionally to get extra security because the other program was not as
strong as GK-Crypt.  If the user then decrypted the file with key 1, and
then with key 2, the file would be completely garbled.  Unless the user
could figure out what had happened, and then unravel all of the steps, the
data would be lost.  (To recover the data, the user would need to encrypt
the data with key 2, encrypt it with key 1, decrypt it with key 2 and
finally decrypt it with key 1.  Any other sequence of steps would garble
the file even further.)

     These types of problems cannot happen with GK-Crypt.  GK-Crypt uses
the cache to prevent all such problems.  It will not let you encrypt a file
twice, or decrypt a file that is not encrypted.  It will not let you
encrypt a file with one key and decrypt it with a different key.

7.5. Double copies

     Another problem with other data privacy packages is that they may make
multiple copies of a file.  They encrypt a file by reading the file one
section at a time, encrypting that portion, and writing the encrypted data
to a new file.  After they finish, they delete the original file.  This
leaves two copies of the file on your disk, the original and the encrypted

     Even though your original file has been deleted, the data is still
there on your disk, and someone could read it.  This problem is insidious,
because the user may never know that it has happened.  The file looks fine
when it is decrypted.  The file looks totally random when it is encrypted.
The user may never realize that copies of the original file are right there
on the hard disk where anyone with a simple utility program can read them.

     GK-Crypt eliminates this problem by writing random gibberish over the
old file before it gets deleted.  This is called shredding the file.

7.6. Partial encryption

     Some other security packages use an alternate approach to prevent your
original data from remaining on your disk.  They write the encrypted data
on top of your original file.  The problem with this solution is if the
power should go down, or even flicker for a few seconds, you will be left
with a partially encrypted file.  It may be possible to recover the data,
if the key is known, but it will take a great deal of work to figure out
the exact spot where the encrypted portion ends and the original data

     GK-Crypt takes a different, safer approach to encrypting a file.  If
the power goes down during encrypting a file, your original file will be
untouched.  You will not need to perform a data recovery process.  You can
proceed as if the power failure never happened.

7.7. Master and cache

     The same safety features that are used for your data files are also
used for the Master File and the cache file.  The new Master File or cache
is always written to your disk before the old one is deleted.

7.8. Adding and renaming files

     Although GK-Crypt takes every possible safety precaution with the
operations under its control, it is still possible for problems to occur
because of things that the user does.

     The first problem occurs if a user renames a file within a group of
encrypted files.  If you are using the GK-Crypt option to base the file key
on the file name, then the file will not decrypt correctly.  You should
never rename a file while it is encrypted.  Only decrypted files can be

     If this problem happens, you can still recover the file if you have a
backup that also contains the Master File and the cache.  The need to make
frequent backups is always important, but it is doubly important when you
are using encryption.

     The second problem occurs if you add a new file within a group of
files that has been encrypted.  Suppose that you have encrypted the file
group *.JPG and then you add a new picture, SHEEP.JPG to the group.  When
you decrypt the group, the file SHEEP.JPG will be decrypted along with all
of the other picture files.  This will leave SHEEP.JPG garbled, because it
had not been encrypted.

     If this happens, get a new copy of SHEEP.JPG from the original source,
or from a backup.  This is perfectly safe when the file and the group are
not encrypted.

7.9. Backups and recovery

     When you are performing a recovery of an encrypted file, it is
absolutely essential that you isolate the backup file, the backup Master
and the backup cache from all other files.  You need to perform the
decryption of the file isolated from all other files so that you do not
decrypt other files that are encrypted with a different key, and you do not
overwrite their Master or cache files.  The recovery should be done in a
separate directory, and preferably on a floppy disk, if possible.  Do not
attempt a recovery of an encrypted file in a directory where there are
other files, or when there is a Master File or cache on the current

     If you have any doubt about how to perform a recovery, seek expert
advice.  Better yet, avoid the need for recovery.  Never rename an
encrypted file, and never add an unencrypted file to an encrypted group.


     In the first chapter of this manual it states that GK-Crypt is far
stronger than any other commercial file encryption product.  This is a bold
claim.  In this chapter the claim will be justified by comparing GK-Crypt
to some other encryption algorithms (methods) that are in widespread use

8.1. The GK-Crypt algorithm

     In order to explain why GK-Crypt is so much stronger than other
encryption algorithms, it will be helpful to explain some of the technical
details of its algorithm.

     GK-Crypt is a secret-key algorithm.  Its strength depends on secret
keys which are known to the legitimate user, but not to an eavesdropper or
intruder.  These secret keys are the Master Key, the cache key, and the
keys for each file group.

     There are two basic kinds of secret-key algorithms, block ciphers and
stream ciphers.  In a block cipher each block of message characters is
subjected to a sequence of substitution, permutation, and combination steps
in order to produce a new block of thoroughly scrambled text.  The
algorithm combines each block of the original message with some part of the
key in a fixed way.

     In a stream cipher there is some method of extending the original key
to generate a stream of key characters as long as the message.  Each
character of the message is combined with the corresponding character of
the key to produce one character of the encrypted message.  In very strong
stream ciphers the next character of the key will depend on both the
original key, and the contents of the message.

     GK-Crypt combines both of these methods.  It uses a very strong block
cipher and a very strong stream cipher.  Either of these encryption methods
taken alone would be much stronger than any current commercial encryption
method.  Combined, they become stronger than nearly all military and
diplomatic encryption methods as well.

     Gk-Crypt treats the contents of your data file as a sequence of
16-character, or 128-bit blocks.  Each block is encrypted using a block
cipher.  The block cipher has a 360-character, or 2880-bit key.  The
original key, which is kept in the cache, is 80 characters, or 640 bits.
This is expanded into a 360-character, or 2880-bit block key.  The
expansion uses non-linear functions, so that the expanded key has no linear
relationship with the original key.

     The block cipher uses 9 rounds of substitutions in which each
character of the block is combined with one character of the expanded key.
Then each character of the block is combined with another character of the
block.  These character pairs are combined using three independent strongly
non-linear functions.  This means that the bits of the output are not
correlated to the bits of the input.

     After each round of substitutions the 16 characters are thoroughly
mixed using a key-dependent permutation.  The 9 rounds insure that every
character of the encrypted block depends on every character of the file
block, and every character of the original key.

     After each block is encrypted a new key block is generated, so that
every block of the file is encrypted with a completely different key block.
The new key is also generated using 9 rounds of non-linear character
combination and key-dependent permutation.  This results in an ultra-strong
stream cipher that combines 16-character data file blocks with
360-character key blocks to produce 16-character encrypted blocks.

     At every stage in the design of GK-Crypt care was taken to make each
element of the encryption as strong as possible.  The substitution tables
were constructed to be as non-linear as possible.  The substitution and
permutation portions of the block cipher use independent keys.  The
generation of the next block key is done using yet a third independent key.
This was done so that if any information about any part of these keys can
be learned by an opponent, that does not reveal anything about the other
parts.  Additional safeguards assure that even if an opponent somehow knew
all of the substitution keys and all of the permutation keys in the block
key, it would still be impossible to determine the next block key or the
preceding block key.

     There is no revolutionary breakthrough here.  GK-Crypt is just a
solidly engineered process combining powerful encryption techniques that
have proved reliable for centuries.  For every conceivable attack on the
encryption, counter-measures have been designed and incorporated.

8.2. AES Advanced Encryption Standard

     AES is an encryption method which was adopted for widespread use after
a lengthy evaluation of some 35 different proposed cryptographic
algorithms.  This might lead people to believe that AES is therefore the
strongest available cryptographic algorithm.  This isn't true.

     The selection process for the AES was based on several criteria
including strength, speed, size, and ease of implementation.  The algorithm
that was chosen, called Rijndael, was judged to have only medium strength.
3 of the 5 finalists in the selection process (Mars, Serpent and Twofish)
were judged to be stronger.  They were not chosen because they were slower,
more complex, or required more storage.  The GK-Crypt algorithm is far
stronger than all 5 of the AES finalists.

     There are several more reasons why GK-Crypt is much stronger than the
AES algorithm.  GK-Crypt was developed several years after AES was made
public.  This means that all the features of AES which made it secure were
known when GK-Crypt was developed.  All of the secure features of AES were
used in GK-Crypt, and several new features were added to make GK-Crypt
vastly stronger than AES.

     AES was necessarily a compromise.  It had to be small and simple in
order to be suitable for use in a broad range of applications, including
tiny low-cost chips imbedded in credit cards, passports, medical ID
bracelets, military ID tags, and so forth.  In the future, even smaller AES
chips may be imbedded in, or printed directly onto banknotes (paper
currency), checks, stock certificates, and similar documents.  Such chips
have very limited storage and computing power, so AES had to be limited in
size to make it fit.  It also had to be kept simple because it was going to
be implemented many times by many different programmers and chip designers,
most of whom have no expertise in cryptography.

     GK-Crypt was designed solely for use on computers.  It does not have
to meet stringent constraints on key size and program size.  So GK-Crypt
can use more storage, take more steps, and use longer keys than AES.  It
was implemented by an expert computer programmer who is also an experienced
cryptographer with several published papers on cryptography, so it did not
need to be small and simple.  (Some of the papers are available online.
Links to these papers can be found at
http://www.contestcen.com/gkcrypt.htm.)  The absence of these size and
complexity constraints make GK-Crypt far stronger than AES.

     In terms of key size and number of steps, GK-Crypt is roughly
equivalent to encrypting 4 times with AES using 4 independent keys.  AES
uses 128-bit keys that are expanded internally to 1024-bit keys.  GK-Crypt
uses 640-bit keys that are expanded internally to 2880-bit keys.  However,
GK-Crypt has some features that make it much stronger than 4 times AES.
For example, GK-Crypt uses a new key for every block of data.  This means
that an opponent cannot accumulate a large number of data blocks that are
all encrypted with the same key.  Many cryptographic systems have been
broken by using a large number of messages encrypted with the same key.
AES is vulnerable to such an attack, but GK-Crypt is not.

8.3. RSA public key cryptography

     The security of the RSA public key algorithm rests solely on the fact
that it is difficult to factor large numbers.  If you are given two
numbers, say 1511 and 1747 it is easy to find their product, 2639717.  It
is much more difficult to go the other way, given a large number to find
the numbers that were multiplied to produce it.  These numbers are called
its factors, hence the factors of 2639717 are 1511 and 1747.  The
difficulty grows the larger the factors get.  When the factors get up to
100 decimal digits or more, it takes a great deal of sophisticated
mathematics and computing time to factor the number.

     The problem with public key cryptography is that it is subject to
advances in mathematics.  A few years ago mathematicians learned how to use
elliptic curves to factor large numbers.  Suddenly many public keys that
seemed totally secure could now be broken, and all of the messages sent
using those keys could now be read.

     The users of public key cryptography had to develop new keys that were
larger than the old keys.  But, for some, it was too late.  Their secret
messages and private files had already been read.

8.4. Quantum cryptography

     The newest development in secret communications is quantum
cryptography.  The method is not available to the public, may never be
available outside of government, and may still be years away from practical
use.  We discuss it here because it has the potential to become an
extremely strong cryptographic method.

     The basic idea in quantum cryptography is that the sender and the
legitimate receiver of a message each have a set of quantum particles that
are "entangled" with each other.  That is, the particles are always in the
same quantum state, even though they may be many miles apart.  A change to
one particle causes the same change to its mate.

     The method has a great advantage, which may also be a fatal flaw.  Any
attempt by an outsider to determine the state of either particle will
change its state, and thus alert the parties that there is an eavesdropper.
However, this property means that an opponent can completely disrupt
communications simply by listening in.  The receiver cannot know if a
change in the particle is a message from the sender or an attempt by
someone else to listen in.  This property, therefore, may doom quantum

Appendix A. DOS BASICS

     GK-Crypt runs under DOS, not under Windows.  DOS was the primary
operating system for personal computers from about 1975 to 1995, and every
computer user of that era knew it well.  Older versions of Windows, prior
to the introduction of Windows 95, ran as tasks under DOS.  However, newer
computer users may not be familiar with DOS, so that a little basic
orientation may be helpful.

A.1. Starting DOS

     On newer computers it may be difficult even to find DOS in order to
use it.  There are two methods for running DOS.  The first method is to
click on a DOS icon from your desktop, or from a taskbar at the top or
bottom edge of the desktop.  The icon may say DOS, or MSDOS, or possibly
CMD or COMMAND.  Clicking any one of these icons will start DOS.  However,
the DOS icon may not be on your desktop or taskbar.  You have to find it.

     You start by clicking on "Start" in the corner of the screen.  This
will bring up a menu listing various programs and options.  If there is a
DOS icon there, you can use it directly, or you could drag it onto the
desktop for future use.  If it is not there, click on "Programs" or "All
Programs."  This will bring up a long list of various programs that are on
your computer.  If one of these is DOS, you can click it, or you can drag
it to the desktop.

     If you still don't see a DOS or CMD icon, put your mouse on each of
the icons that you see.  Don't click, just let the mouse cursor rest on the
icon.  This will often bring up another list of programs, and DOS may be
among them.

     If DOS still is not there, don't give up.  In the list of All Programs
there will be some folders with names such as "Applications" or "System
Utilities."  Click to open each of these folders.  In those folders you may
find DOS or CMD.  Or, you may find more folders.  Again, rest the mouse on
the names of programs, and click on folders to find even more well-hidden
programs and folders.

     Once you find the DOS icon, drag it to the desktop.  Put the mouse
cursor on the icon and hold down the left button.  Move the mouse to drag
the cursor onto the desktop, and then release it to drop the icon on the
desktop.  Click the desktop to close all of the other windows.  Then drag
the DOS icon to wherever you want it on the desktop.

     If all of this fails, it is time to try the second method.  Go back to
the desktop, and click on "Start" again.  In the list of options click on
"Run" or "Run Program."  This will open a small window with a box where you
can type the name of a program that you wish to run.  Type CMD in this box,
and then press Enter.  This will open a DOS window.

A.2. Sizing the DOS window

     The DOS window will often be a small window in the middle of the
screen, probably off-center.  It is easier to work with DOS in full-screen
mode, with no distracting windows or borders.  To do this, right click on
the border of the DOS window, and select "Properties" from the pop-up
window that appears.  Use the various options to select full-screen mode.
This may take several tries before it works, so don't get frustrated if the
next time you use DOS you get the same small window, and need to resize it

     When you do get the full screen mode, the screen is likely to be set
to 50-line mode.  This make the characters small and crudely formed.  You
may be more comfortable using 25-line mode.  To switch, you can type the

     mode con lines=25

This will double the size of the characters and make them easier to read.

A.3. Directories

     In DOS your computer's hard disk is organized into directories.  All
of the files on your computer are in directories.  These correspond to the
folders in Windows.  Directories and folders are the same thing.  A
directory or a folder can contain files and more directories or folders, so
that the folders or directories are nested one inside the other in a

     The top of the hierarchy is called the "root directory."  Typically
the root directory does not contain any files.  Rather, it contains all of
the principal directories on the computer, such as

     \Program Files\
     \Documents and Settings\

and so forth.  The backslash \ in front of these directory names shows that
they are directories within the root directory.

     A directory within another directory is sometimes called a
subdirectory.  In the example above the directory Windows would be a
subdirectory of the root directory.

A.4. Current directory

     Files are identified in DOS by using a path, a filename and a
filetype.  For example,


Here the path is direc1\direc2, the filename is file1 and the filetype is
doc.  The path consists of the sequence of nested directories which contain
the desired file.

     If the path starts with a \ backslash, then the sequence of
directories start from the root directory.  If the backslash is omitted,
then the path starts from the current directory.  For example, if the
current directory is Windows, then the file identifier
direc1\direc2\file1.doc would refer to the file

     By setting the current directory you can shorten the names of programs
and files that you must type.  For example, if you want to use the program


to process the data files


you could type

    \direc1\direc2\prog1 \direc1\direc2\file1.dat \direc1\direc2\file2.dat

If you changed the current directory to \direc1\direc2 then this could be
shortened to

    prog1 file1.dat file2.dat

    The command to change the current directory is cd.  To change the
current directory to \direc1\direc2 you would type

     cd \direc1\direc2\

If you then wanted to change the current directory to \direc1\direc2\direc3
it is sufficient to type

     cd direc3

since you were already in the directory \direc1\direc2.

A.5. Working with directories

     You can make your own directories by using the Make Directory command.
For example, if the current directory is \direc1\direc2 and you wanted to
make a subdirectory called direc3, then you could type

     md direc3

Starting from the root directory, the new directory would be

     To remove a directory, you can use the Remove Directory command.  For
example, to remove the directory \direc1\direc2\direc3 you would type

     rd \direc1\direc2\direc3

As a safety precaution, you cannot remove a directory until you have
deleted all of the files in the directory, and removed all of its
subdirectories.  This prevents you from accidentally deleting files that
you meant to keep.

     To list the contents of a directory, you can use the Directory
command.  The basic format is

     dir mydirec /options

Here mydirec is the directory you want to list.  There are many possible
options.  Here are a few of the most useful:

     /s    List the contents of all subdirectories
     /on   Sort the files by name
     /os   Sort the files, smallest to largest
     /o-s  Sort the files, largest to smallest
     /od   Sort the files, oldest to newest
     /o-d  Sort the files, newest to oldest
     /p    Pause after every 20 lines

You can use several options in the same command.  For example,

     dir \direc1 /s /od /p

would list the files in \direc1 and all of its subdirectories sorted from
oldest to newest, and pausing after every 20 lines.

     You can also list specific files, files that have a given filename or
filetype, or files whose filenames and filetypes begin with specific
letters.  Here are some examples

     dir tax.ref   Lists the file tax.ref.
     dir tax.*     Lists all files with the name tax.
     dir *.doc     Lists all files of type doc.
     dir st*.c*    Lists all files whose filename starts with st
                   and whose filetype begins with c, such as
                   startup.cfg, study.com or state.core.

The * asterisks in these commands are called wildcards because they can be
replaced by any set of letters.  These commands can tell you whether these
files exist, their sizes, and the date they were last updated.

A.6. Identifying files

     All of the data in your computer resides in files.  Files contain the
operating system, all of the application programs, and all of the data that
they use and create.  Files are identified to DOS by four fields, namely
the drive, path, filename and extension.

     drive      is the device where your file is stored, usually
                C for your hard drive, A or B for a floppy drive,
                D or E for a CDROM drive.

     path       is the directory on your drive where the file is

     filename   is the name that you gave your file.  The name
                usually indicates the contents or purpose of the

     extension  is a suffix that indicates the kind of file, such
                as TXT for a text file, JPEG for a picture file,
                EXE for an executable file, etc.

A full file identifier might look like this,


     In this example, c: identifies that your file is on the C drive, which
is your hard drive.  \mycompany\mydepartment\2005\ is the path to your
data.  It shows that the data file is located in the 2005 folder, which is
inside the mydepartment folder, in the mycompany folder.  So the path
consists of nested folders, or a list of directories.  sales.wp is the file
with the data.  The filename is sales, and the extension is wp, which
indicates that it is a WordPerfect document.

     In a file identifier all of the fields except the filename are

     drive      can be omitted if the file is on the current
                drive, that is, the drive where you are now

     path       can be omitted if the file is on the current
                directory of the drive.

     extension  can be omitted if the file does not have an
                extension on its name.  For example, if the file
                is just named oldstuff then no extension is

Here are some examples of valid file identifiers:

          identifies the file budget in the current directory
          of the A drive.

          identifies the file commissions in the jones directory
          on the current drive.

          identifies the file requests.txt in the late
          subdirectory of the current directory.

A.7. File operations

     Besides the encryption and decryption operations that you perform
using GK-Crypt, it can be useful to know several other common file

     There is no DOS operation to create a file.  Files are created by
application programs such as word processors, picture editors,
spreadsheets, etc.  Once created, files can be copied, renamed and deleted.

     It is important to remember that encrypted files should not be
renamed, and files should not be copied into or out of a group of encrypted
files.  It is safest to decrypt files before renaming or copying.

     To copy a file to a new location, the command is

     copy oldfile newfile

The old file and new file identifiers can be fully qualified, that is, they
may have drive, path, filename and filetype.  So the copy command can be
used to copy files to other directories or to other drives.

     Wildcards can be used in the copy command to copy groups of files.
For example, the command

     copy \oldpath\*.doc \newpath\*.*

would copy all files of type doc from the \oldpath directory to the
\newpath directory.

     The rename command works similarly to the copy command.  The form is

     ren oldfile newname

Here oldfile can be fully qualified, with drive, path, filename and
filetype.  However, newname can have only a new filename and filetype.
There cannot be a new drive or new path because the file does not change
its location, only its name and/or type.  For example,

     ren target\x3*.jpg x4*.*

would rename all of the jpg files in the target directory that start with
x3 to start with x4.

     The command to delete files takes the form

     del file

Here, file can be a fully-qualified file identifier, with drive, path,
filename and filetype.  It can also have wildcards so that you can delete
several files with a single command.  For example,

     del a:old*.*

would delete all files in the current directory of the a drive whose
filenames start with old.

     Note that deleting a file does not erase it.  The file still exists on
the disk, where it can be read by various utility programs that are
available for that purpose.  The file will remain there until some other
file eventually gets written on top of it.

     There are many other DOS commands and options.  This is just a small
sample of useful DOS commands.

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© Copyright 2005-2007 Master Software Corporation
All rights reserved. No part of this manual may be reproduced in any form without the express permission of the author.