OP-Crypt Message Encryption System Version 01
User Manual - November 29, 2012


     OP-Crypt is a powerful new software system that uses the unbreakable
One-Time Pad encryption algorithm.  This algorithm is the only encryption
method that has been proven mathematically to be unbreakable.  Without the
keys, nobody, no matter how much computer power they possess, can ever read
your messages.

     This means that you can communicate with absolute security.  Your
messages are safe forever, provided the keys remain secret.

     For over 50 years the one-time pad encryption algorithm has been the
standard of security for cryptographic products.  Other products claim to
be "like the one-time pad" or perhaps "as secure as the one-time pad" even
when they are not at all similar to the one-time pad.  OP-Crypt is the
one-time pad, the real thing, the algorithm that so many others try to


  1.1. The One-Time Pad
  1.2. Networks and stations
  1.3. Maximum security

  2.1. Installation password
  2.2. Network key
  2.3. Master key
  2.4. Station keys
  2.5. Message ID
  2.6. Key summary

  3.1. Star network
  3.2. Hierarchical network
  3.3. Cluster network
  3.4. Pairwise network
  3.5. Special stations
  3.6. Distributing keys

  4.1. Encrypting a message
  4.2. Decrypting a message
  4.3. Station information
    4.3.1. Adding a station
    4.3.2. Changing a station key
    4.3.3. Deleting a station
    4.3.4. Listing the station names
  4.4. Changing the master key
  4.5. Changing the network key

  5.1. Starting the installation
  5.2. Installation password
  5.3. Software license
  5.4. Network key
  5.5. Master key
  5.6. Completing the installation

  6.1. Key Do's and Don'ts
  6.2. Letters, digits and punctuation
  6.3. Key blocks
  6.4. Pronounceable keys
  6.5. Patterns
  6.6. Secretaries and clerks
  6.7. Key strength
  6.8. Summary: Picking a key

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. Long names
  A.8. File operations
  A.9. Batch files

1.1. The One-Time Pad

     The reason that the One-Time Pad algorithm is so secure is that it
uses a separate key from the key stream for each character of the message.
A million-character message would use a million keys from the key stream.
Any character in the message could get changed into any other character,
completely independently.  So the first A in the message could become W,
the second A could become # and the third A could become 3, for example.

     Every message uses a different set of keys.  If you sent a second
message of one million characters, that message would use a different
million keys from the key stream.  If you sent exactly the same message
again, the first A in the message could become ], the second A could become
6 and the third A could become h, for example.

     The problem with classical one-time pad systems is that you eventually
run out of keys.  Then you need to supply new keys to all of the parties --
but how can you keep the new keys secret if you have run out of keys?  You
cannot use the one-time pad to send new keys because you need one key to
protect each key that you send.  For every new key you distribute you use
up one key.  You can never get ahead.

     OP-Crypt does not have this problem.  It uses an infinitely long key
stream.  No matter how many messages you send, and no matter how long your
messages are, you can never run out of keys, and you never need to reuse
keys, or to distribute more keys.  The key stream is infinitely long, so it
never gets used up.

     OP-Crypt, however, is much stronger than the basic One-Time Pad.
Op-Crypt first performs a One-Time Pad encryption, as described above.
Then it performs a block encryption, and then a second, independent,
One-Time Pad encryption.  Triple encryption.  The result is a uniquely
powerful encryption, completely and permanently unbreakable.

1.2. Networks and stations

     OP-Crypt is designed for use by a group of people who need to
communicate secretly with one another.  The entire set of users is called a
network.  The network may be any type of organization, commercial, social,
diplomatic, professional, military, religious, or any other.  Each party
within the network is called a station.  A station may be an office of a
company, a department of an organization, a branch, an embassy, an agency,
an individual, or simply an email address.

     Within a network, an office or person could operate several different
stations for communications.  Thus the same individual could be Larry, El
Paso, and oilman@sym3.net.

1.3. Maximum security

     OP-Crypt has been designed for maximum security.  Every file that
OP-Crypt uses is securely encrypted.  Every file that OP-Crypt produces is
securely encrypted.  It has been designed to leave no openings and no
weaknesses that any potential opponent could use to breach the system.  All
of the different encryptions require a lot of different keys.  The
following sections describe all of the different types of passwords, keys
and identifiers that OP-Crypt uses to achieve such extreme security.


     OP-Crypt uses a system of passwords and keys to assure that your
messages remain secure, even if other parties had the OP-Crypt software,
and even if they obtained your disks or possibly your computer itself.

     There are five different kinds of passwords and keys, so you might
think that you will need to memorize and endlessly type a whole array of
keys.  Be assured, right from the outset, that the only key that you need
to memorize is the master key, which you choose yourself.  The other keys
are either generated by the software, or they are typed only once when
OP-Crypt is installed at each station.

2.1. Installation password

     There is one password used with OP-Crypt, namely the installation
password.  This password is required to install the OP-Crypt software.  If
somebody were to obtain the distribution disk with your copy of the
OP-Crypt software, they would not be able to install it on their own
computer without this password.  (OP-Crypt can NOT be distributed over the
Internet because of export restrictions.  We must verify that OP-Crypt is
being sent to a mailing address in the USA or Canada.)  The installation
password is 14 characters, and has the form xxxx-xxxx-xxxx, where each x
can be either a letter or a digit, for example, A1B2-CD34-E56F.

     IMPORTANT:  The OP-Crypt distribution disk is normally mailed with the
installation password in the same package.  If you would like the
installation password mailed separately, perhaps to a different address,
please notify Master Software when you order.  The installation password
will be mailed in a plain, unmarked envelope with no return address.  It
can also be emailed to an anonymous email address.  There is no charge for
the second mailing.

2.2. Network key

     When you install OP-Crypt you must supply the network key for your
network.  It is essential that you choose a strong network key.  You should
carefully read the chapter on choosing keys before you select your network

     The network key is the same for every station within your network.  It
is used to mix the encryption tables.  This personalizes OP-Crypt for your
network.  Every station in your network must use the same encryption tables
so that they can communicate.  Other purchasers of OP-Crypt who do not know
your network key cannot read your messages, and you cannot read their
messages.  The encryption tables that you use in your network are produced
using your network key to mix the encryption tables that Master Software

     It is vital that you choose a strong network key.  You should read the
chapter on choosing keys before selecting your network key.  To make
certain that every station types the network key correctly, OP-Crypt
generates a 4-digit verification code.  When you send the network key to a
station, you should also send the verification code to avoid costly errors.
It is also a good idea to send and return a test message to each new
station to verify that the key was entered correctly.

2.3. Master key

     When the encryption tables are stored on your computer they are
encrypted using strong 640-bit keys generated by OP-Crypt.  These keys are
never seen by the user.  They are kept in a special file called the master
file.  The master file is encrypted by a master key chosen by the user.
Every station can choose a different master key.  The master keys are not
shared or distributed.  For maximum security no station should know the
master key of any other station.

     The master file and the master key are the heart of the system.  If
someone could obtain both your master file and your master key, they would
have complete access to all of your files and messages.  They would even
have access to your station key file, so it is possible that they could
read messages between other stations.

     It is therefore absolutely essential that every station chooses a
strong master key.  A weak master key at one station would compromise the
entire network.  Carefully read the chapter on choosing keys before you
select your master key.

2.4. Station keys

     Each station has a station name, or ID, and a station key.  The
station ID can be public.  It can be used openly in emails, letters and
phone calls.  The station ID can be up to 20 characters long, and may be
anything you find convenient to identify your correspondents.  Examples are
Charlie, Austin branch, red-dog, Bosley Bank Ltd, Eagle 1, Smith's Grocery,
Sister Divinity, and so forth.

     For each station ID there is a corresponding station key.  These keys
should be kept strictly secret.  Follow the rules in the Keys chapter for
choosing strong keys.  The station ID and station key are typed just once
for each station.  OP-Crypt remembers them for you in a securely encrypted

2.5. Message ID

     The key for each message is built by OP-Crypt from a message ID chosen
by the user.  The message ID should be completely random, and at least 10
characters long.  It is not a safe practice to vary the message ID in some
systematic way, like numbering the messages sequentially, or obtaining the
message ID from the date and time.  Some sample message IDs might be 

     D4Z7 U8C9 J3Y5

     The message ID does not need to be secret.  It can be included in the
body or subject line of an email or letter that accompanies the message
file.  OP-Crypt will use the station key of the sender, the station key of
the receiver, and the message ID to construct a secure message key.  So, if
the message is sent as an attachment to an email, the email should contain
these 3 identifiers worked into its text (unless the sender ID and/or the
receiver ID can be determined from the email addresses).

2.6. Key summary

     The following table gives a quick overview of the different passwords
and keys used by OP-Crypt.  

Installation password
     Generated by Master Software
     Typed once at installation
     Never used again
Network key
     Chosen by the users
     The same for all stations
     Typed once at installation
     Can be changed later
Master key
     Chosen by each user
     Different for each station
     Typed at every session
Station keys
     Chosen by the users
     Typed once for each new station added
     Can be changed later
Message ID
     Chosen by the message sender
     Different for every message
     Typed once by sender, once by receiver


     Before you install OP-Crypt, and before you begin to distribute keys,
you need to consider how you want to set up your network.

     If the network is small, if every station knows about every other
station, and if you want all of the stations to be able to communicate
freely with each other, then there is no decision required.  You simply
distribute the network key and all of the station keys to everyone.

     If the network is large, and you do not want every station to know
about and communicate with every other station, then you should consider
other ways of organizing your network.  The following sections describe
some of the possibilities.

3.1. Star network

     In a star network, all communications flow from one central station,
called the network hub, to all of the other stations.  In this model, none
of the stations know about any other station except the hub.  Each station
receives only the network key, the station key for the hub, and its own
station key.  Normally all of the keys are chosen by the hub.

     In a star network none of the outer stations can communicate directly
with each other, and none of the outer stations has the ability to read any
of the messages sent between the hub and any other station.  If one outer
station needs to send a message to another station it must be relayed
through the hub.  The hub will decrypt the message using the sender's ID,
then re-encrypt it using the receiver's key and a different message ID.

3.2. Hierarchical network

     In a hierarchical network there is also one central station, but some
of its outer stations may have their own networks, also organized as star
networks.  This may continue for several layers.  Each station may
communicate with its own local network and with its hub.

     In the centralized model, there will be one network key for the entire
hierarchy.  The central hub chooses all of the station keys, and
distributes the appropriate set of keys to each station, according to its
place in the network.  Each station can communicate up the hierarchy as far
as the central hub, and down the hierarchy to the stations below it.
Stations cannot communicate across the hierarchy, or read messages sent in
other parts of the network.

     In the decentralized model, there may still be just one network key
for the whole hierarchy, or each local star network could have its own
network key.  In the latter case, each station can communicate only one
level up and one level down the hierarchy.  A station in the middle of the
hierarchy, one which is neither the central hub, nor at the outermost
layer, will require two separate copies of OP-Crypt with two separate sets
of encryption files, one for communicating up the network, and one for
communicating down.

     In a decentralized network, each local hub will select and distribute
the station keys for its own outer stations.  Stations elsewhere in the
hierarchy, even stations higher up, will not know either the network key or
the station keys for any other local star network.  No station will be able
to communicate with, or to read the messages of, any other station outside
of its own local star.  Even messages from the central hub will need to be
relayed down the hierarchy through all of the intermediate hubs.

3.3. Cluster network

     In a cluster network, certain groups of stations will communicate
directly with one another.  Each station in a cluster will know the names
and keys of every other station in its cluster.  Typically, each station
will choose its own station key and distribute that key to the rest of the
cluster.  The clusters themselves might be organized as a star network or a
hierarchy.  For example, all of the stations in each geographic area may
form one cluster, while all of the clusters are controlled from a single
central hub, or headquarters.

3.4. Pairwise network

     Some pairs of stations in a network may have a larger volume of
message traffic which may justify having special station names and keys for
that traffic.  For example, the Dallas office may have heavy communications
with the Fort Worth office.  So the Dallas office may be known by the
station name Dallas to the rest of the network, but to the Fort Worth
office it may be known as TexHQ.

3.5. Special stations

     In larger networks it may be desirable to reserve some station names
for special purposes.  One such purpose might be to broadcast messages,
where the hub wants to send the same message to every station, but does not
want to take the time to encrypt it separately for each station.  In this
case it could use a special broadcast station name, and send the message to
all of the stations using that name for the receiving station.  That way,
only one encrypted copy of the message would need to be generated.

     Another special station name might be used for distributing keys, for
example when changing the network key or adding new stations.  The use of
the alternate station name would alert the receiver to the special nature
of the message.  Such a message might have a special structure that
conceals its purpose, for example hiding the key inside some completely
innocent text.

3.6. Distributing keys

     Once the network is set up new keys can be distributed using messages
encrypted by OP-Crypt.  But, how do you distribute keys before your network
is set up?  How do you distribute keys to a new station that has not yet
joined the network?

     If you already have a message encryption system, and you are upgrading
to OP-Crypt, then you can distribute keys through the old system.  Suppose,
though, that you are upgrading because you no longer trust your old system.
Then it would be foolish to use the old system to distribute keys for the
new system.

     A better way to distribute keys is by encrypting them with NK-Crypt.
This is another product offered by Master Software.  NK-Crypt has the
advantage that it does not require any exchange of keys.  It avoids the
problem of what key to use when sending the first secret key.  So you can
use NK-Crypt to send the new station the network key, its station name and
station key, and the hub's station name and key.  Once this initial setup
is completed you can use OP-Crypt to send the other station names and keys.


     Although there are many keys and many files involved with OP-Crypt,
using OP-Crypt is really very easy.  The program tells you at every stage
what needs to be done.  You choose the actions, such as encrypting and
decrypting messages, and the program tells you what file names, keys and
ID's are needed.

     To start OP-Crypt, you type the OP command at the DOS prompt.  That
is, you type 


and then press the Enter key.  The first time you run OP-Crypt it will
install itself.  That will be explained in a later chapter.

     OP-Crypt will ask you what you want to do.  The choices are as follows

     Do you wish to
       E - Encrypt a message.  Make it unreadable to send it.
       D - Decrypt a message.  Read a received message.
       S - Edit station keys (add, delete, change).
       M - Change master key.
       N - Change network key.
       Q - Quit.

     Type your choice (E, D, S, M, N or Q):

You type a letter to indicate your choice.  For example, if you want to
encrypt a message, you would type E.

4.1. Encrypting a message

     To encrypt a message you need to supply 5 pieces of information.  Once
you have typed E to select "Encrypt a message" OP-Crypt will prompt you for
each item.

     The first item is the name of the file that contains your message.
You can create the file the same way you create any file on your computer,
for example by using a text editor or a word processor.  You do not need to
be concerned about the format of the file.  OP-Crypt can handle any file in
any format created by any program.  You will be prompted for the file name 

     Enter the name of the message file to be encrypted,
     for example \MESSAGES\NEWMESSAGE.TXT or type Q to quit.

     File name:

Type the name of your message file and press Enter.  For example, if you
want to encrypt the file munitions.list then you would type munitions.list
like this 

     Enter the name of the message file to be encrypted,
     for example \MESSAGES\NEWMESSAGE.TXT or type Q to quit.

     File name: munitions.list

and then press Enter.

     Next you need to give the name of the file where you want OP-Crypt to
put the encrypted message.  You may use any file name you wish.  

     Enter the name for the resulting encrypted file, for example
     \ALBUM\PHOTO36.JPG or type Q to quit.

     File name:

Type the name of the result file and press Enter.  For example, if you want
the encrypted file to be called birthday then you would type birthday.
After the encryption process is finished, you would send the file birthday
to the receiving station.  You will need to tell the receiver the message

     Note that OP-Crypt does not erase or over-write the files that you
encrypt.  In the example above, the original unencrypted message would
still be in the file munitions.list and the encrypted message would be in
the file birthday.  This allows you to send the same message to any number
of stations, with each copy encrypted for that station.

     Bear in mind, however, that when the encryption process is finished,
the message file is still there on your computer.  If an opponent could
possibly have access to your computer, the message file should be either
shredded or encrypted.  It is not sufficient simply to erase the file,
since it would remain on your hard drive.  You could use GK-Crypt to
encrypt the file.

     The next steps in the encryption are to give the station ID of the
sender (your own station), the station ID of the receiver (the station you
are sending to), and the unique message ID.  You type this information when
you receive the following prompts:  

     Enter the station ID of the message sender.
     Sender ID:

     Enter the station ID of the message receiver.
     Receiver ID:

     Enter the message ID.  Every message should have a unique
     message ID at least 10 characters long.  The message ID is
     case-sensitive, so west, West and WEST are all different.
     Message ID:

The station ID that you enter can be any station ID that you have
previously set up.  A later section describes how you set station IDs.

     The message ID should be completely random and at least 10 characters
long.  Every message sent in your network must have a different message ID,
for example, KZX 937 UDF 491.  It is not safe to form the message ID in any
systematic way.

4.2. Decrypting a message

     Decrypting a message is the opposite process from encrypting the
message.  You enter the same information in a slightly different order.
The first file name that you type will be the file containing the encrypted
message that you received.  The second file name that you type will be the
file where you want OP-Crypt to place the decrypted message so that you can
read it.

     You select the decryption task from the main menu by typing D for
Decrypt a message like this, 

     Do you wish to
       E - Encrypt a message.  Make it unreadable to send it.
       D - Decrypt a message.  Read a received message.
       S - Edit station keys (add, delete, change).
       M - Change master key.
       N - Change network key.
       Q - Quit.

     Type your choice (E, D, S, M, N or Q): d

     OP-Crypt will prompt you for the name of the file that you want
decrypted.  This is a message file that you have received from the sending

     Enter the name of the message file to be decrypted,
     for example \MESSAGES\NEWMESSAGE.TXT or type Q to quit.

     File name:

If the message file is called birthday you would type birthday and press

     Next, OP-Crypt prompts you for the name of the file where you want the
decrypted message to be placed.  Depending on what type of software was
used to create the file, it may be important that the decrypted file have
the same file type as the original file.  For example, if the original file
was created by WordPerfect it would have the file type wp, for example
merger.wp.  If you are going to read the file using WordPerfect then the
decrypted file should also have the file type wp, for example newplan.wp.  

     Enter the name for the resulting decrypted file, for example
     \ALBUM\PHOTO36.JPG or type Q to quit.

     File name:

     As with the encryption process, you will be prompted for the name of
the sending station, the name of the receiving station, (your own station),
and the message ID.  The sender should have sent you the message ID along
with the message.  For example, it might be contained somewhere within an
email that had the encrypted message attached.  You type this information
following the prompts 

     Enter the station ID of the message sender.
     Sender ID:

     Enter the station ID of the message receiver.
     Receiver ID:

     Enter the message ID.  Every message should have a unique
     message ID at least 10 characters long.  The message ID is
     case-sensitive, so west, West and WEST are all different.
     Message ID:

The decrypted file will be placed in the file you chose.  You are
responsible for deleting or securing that file after you have read the
message.  For example, if you plan to keep the file, you may encrypt it
using GK-Crypt.  Alternatively, you may delete and shred the file, and
create it again when it is needed by using OP-Crypt to decrypt the message

4.3. Station information

     To create or change information about the stations in your network you
would select S - Edit station keys from the main menu.  

     Do you wish to
       E - Encrypt a message.  Make it unreadable to send it.
       D - Decrypt a message.  Read a received message.
       S - Edit station keys (add, delete, change).
       M - Change master key.
       N - Change network key.
       Q - Quit.

     Type your choice (E, D, S, M, N or Q):

At the prompt you type S.

     This will select the station editing function.  You can use it to add,
delete or change network stations.  OP-Crypt will prompt you like this 

     Do you wish to
       A - Add a new station.
       C - Change a station key.
       D - Delete a station.
       L - List the stations.
       Q - Quit.

     Type your choice (A, C, D, L or Q):

You type the letter indicating your choice.

4.3.1. Adding a station

     You add a new station by giving the station name, or station ID, and
the station key.  The station name is any name that you choose to identify
one of the parties in your network.  The station names should be names that
are meaningful to you and easy to remember.  It is not necessary to make
them cryptic or random, or to keep them secret.  The station names may be
used freely in open communications, such as emails that accompany your
secret messages.

     The station keys, however, should be kept strictly secret.  They
should be long strong cryptographic keys.  It is not safe to build the
station keys from the station names in any type of systematic way.  For
example, if your stations are called red, white and blue it would be
completely unsafe and unwise to make the station keys red-key, white-key
and blue-key or xzq:red, xzq:white and xzq:blue or r/ED, whi/TE and bl/UE
or any similar nonsense.

     Don't cut corners.  Follow the rules in the chapter on keys and always
use strong keys.

     When you have selected A to add a station OP-Crypt will prompt you for
the station name.  

     Enter the station name (station ID).
     The name may be 1 to 20 characters.
     Station name:

The station name is not case-sensitive.  The names charley, Charley and
CHARLEY are all equivalent.  You may type the station name in upper case,
lower case or mixed case, as you wish.

     After you have entered the station name, OP-Crypt will ask for the
station key.  

     Enter the station key.  The key may be 1 to 126 characters.
     The key is case-sensitive, so west, West and WEST are
     3 different keys.  Or, type Q to quit.
     Station key:

The station key must be entered exactly.  All characters count, including
blanks.  The key is case-sensitive.

     To help insure that each station key is entered correctly, every
station key has a 4-digit verification code.  Suppose that station Bravo
has chosen the station key SDV8493tz5967Wh.  When station Bravo adds this
key to its own station list, OP-Crypt will display the verification code
9179 like this 

     The key verification code is 9179.  Is this correct?
     Type Y or N:

They should carefully inspect the station key that was entered.  If it was
typed correctly they would type Y to accept the key.

     When station Bravo distributes the station key SDV8493tz5967Wh to
other stations, they should also distribute the verification code 9179.
When another station adds station Bravo to its station list, they should
check the verification code to make sure it matches.  Let's say they get 

     The key verification code is 4308.  Is this correct?
     Type Y or N:

This does not match, so they should type N.  This means they did not type
the station key correctly.  OP-Crypt will give them another chance to type
the station key.

     Each station key needs to be typed only once.  After the station key
has been entered and verified OP-Crypt will remember it, so it will not
need to be typed again.

4.3.2. Changing a station key

     Changing a station key works similarly.  OP-Crypt prompts for the
station name.  

     Enter the station name (station ID), or Q to quit.
     Station name:

You type the station name and press Enter.  The name may be typed in upper
or lower case.

     OP-Crypt will then prompt you for the new station key.  This should be
a strong key, using the guidelines in the chapter on keys.  

     Enter the new station key.  The key may be 1 to 126 characters.
     The key is case-sensitive, so west, West and WEST are considered
     3 different keys.  Or, type Q to quit.

     Station key:

     To be certain that you have typed the station key correctly, OP-Crypt
will display the verification code.  When a station key is first created,
the verification code should be recorded.  When the station key is sent to
other stations, the verification code should also be sent so the other
station can be sure the station key was sent and typed correctly.  For

     The key verification code is 1234.  Is this correct?

     Type Y or N:

If the verification code matches, type Y for Yes.

     When a station key is first created the verification code should be
recorded.  When the station key is sent to other stations, the verification
code should also be sent so the other station can be sure the station key
was sent and typed correctly.

4.3.3. Deleting a station

     The procedure to delete a station is straightforward.  You simply
specify the station name after the prompt 

     Enter name (ID) of the station to be deleted.

     Station name:

To delete station W:Smith you would type W:Smith and press Enter.  Station
names are not case-sensitive, so you can type them in upper case, lower
case, or mixed case, as desired.

4.3.4. Listing the station names

     Selecting L from the Station Editing menu will list all of the station
names.  The list is written to the file OPCRYPT.LST.  You can use the list
to decide whether any stations should be deleted, or to find any station
names you may have forgotten.

4.4. Changing the master key

     Stations should change their master keys regularly.  The master key
should be changed any time someone who has access to the master key leaves,
and any time there is a suspicion that some unauthorized person may have
obtained the master key.  This prevents the person from coming into your
premises, copying files from your computer, and then reading them.
Depending upon how your network is organized, somebody who obtained your
master key and master file might also be able to read messages between
other stations.

     To change the master key you would select M - Change master key from
the main menu.  

     Do you wish to
       E - Encrypt a message.  Make it unreadable to send it.
       D - Decrypt a message.  Read a received message.
       S - Edit station keys (add, delete, change).
       M - Change master key.
       N - Change network key.
       Q - Quit.

     Type your choice (E, D, S, M, N or Q):

At the prompt you type M.

     OP-Crypt will prompt you to enter the new master key.  

     The Master Key is case-sensitive.  For example, the 6 words
        sample   Sample   SAMple
        SAMPLE   SamPle   SamplE
     are all considered different keys.  All characters are taken
     as part of the key, including leading and trailing blanks.

     Please enter the new Master Key.

The master key must be typed exactly.

     You should carefully examine the master key to be sure that you have
typed it correctly.  If you type it incorrectly, and you do not remember
exactly how you typed it, then you will be unable to use OP-Crypt.  You
will have to restore the OP-Crypt files from a backup.  OP-Crypt will give
you the chance to correct any errors.  

     Please check the Master Key carefully.

     Is the Master Key correct?  (Y or N):

Here xxxx is the key you typed.  If it is correct, type Y, otherwise type

     It is so important that you type the master key correctly, that
OP-Crypt will give you a second chance to verify the key.  

    For verification, please enter the new Master Key again.


Type the master key again.  If it matches, then OP-Crypt will change to the
new master key.  If the two keys do not match, OP-Crypt will display 


You will then be given a chance to repeat the process.  You should type the
master key more slowly and carefully the second time.

4.5. Changing the network key

     From time to time you may decide to change the network key.  Some
experts recommend changing the network key every day.  This means that an
opponent who somehow obtained the network key would be able to read
messages that were intercepted only on a single day.  Another approach is
to change the network key only when there is physical evidence that the
network has been compromised, for example if a lock has been forced, or
disks are missing.

     To change the network key you would select N - Change network key from
the main menu.  

     Do you wish to
       E - Encrypt a message.  Make it unreadable to send it.
       D - Decrypt a message.  Read a received message.
       S - Edit station keys (add, delete, change).
       M - Change master key.
       N - Change network key.
       Q - Quit.

     Type your choice (E, D, S, M, N or Q):

At the prompt you type N.

     OP-Crypt will prompt you to enter the new network key.  

     Please enter the new network key.  The network key may be up
     to 126 characters long.  The network key is case-sensitive, so
     abcd and ABCD are not equivalent.  All characters count,
     including blanks.

     Network key:

The network key must be typed exactly.

     To be certain that the network key has been entered correctly a
4-digit verification code is used.  When the hub station distributes the
new network key, they should also distribute the verification code.
Op-Crypt will display the code, for example 

     The verification code is 9999

     Is this correct?  (Y or N):

If the verification code matches, type Y for Yes.

     All stations must change the network key at the same time.  If one
station sent a message to another station using an older or a newer network
key, the receiving station would be unable to decrypt the message.


     The first time you use OP-Crypt it will install itself.  The first
step in installation is to copy the OP-Crypt files from the installation
disk to your hard disk.

     Place the distribution disk in your CD-ROM drive.  You can copy the
file using Windows or using DOS.  To copy the files using Windows, click on
My Computer on your desktop, and then click on your CD-ROM drive.  For each
file, follow these steps:  (1) Put the cursor over the file to highlight
it.  (2) Click on Files on the toolbar.  (3) Click on Copy.  (4) Follow the
hierarchy of folders until you reach the folder where you want to install
OP-Crypt.  (5) Click on Copy again.  Alternatively, in step 1 you could
hold down the Ctrl key and hover the cursor over each file in turn before
performing the other steps.

     It is much easier to copy the files using DOS.  Suppose that your
CD-ROM drive is your d drive, that your hard drive is your c drive, and
that you have chosen to install OP-Crypt in a directory called \vacation.
Then you would copy the files to your hard drive by typing the command 

     copy d:*.* c:\vacation\

That will copy all of the files in one step.

5.1. Starting the installation

     Once OP-Crypt is on your disk, you can run it from DOS by typing the
OP command, like this 


The first time you run OP-Crypt it will take you through the installation
procedure.  It will first ask if you are ready 

     OP-Crypt Program Installation
     During the installation you will need to choose the Master Key.
     Please consult the OP-Crypt User Manual before making this
     important decision.

     Do you wish to continue the installation now?
     Choose (Y or N):

If you are ready to proceed, type y.

5.2. Installation password

     To install OP-Crypt you must supply the installation password.  This
protects you from somebody obtaining your distribution disks and installing
OP-Crypt to read your messages.  OP-Crypt will ask 

     Please enter the installation password.  The password
     is enclosed with the distribution disk.  The password
     is 14 characters long, for example A123-B456-C789


Type the 14-character installation password that you have been sent,
including the two hyphens.

     As a precaution, you may request that the installation password be
sent separately from the distribution disk, possibly to a different mailing
address.  It can be sent in a plain white envelope with no return address.

5.3. Software license

     The next step is to read the Software License.  OP-Crypt will display 

     The OP-Crypt Message Encryption System may be used only under
     the terms of the Software License.  Please select:

     A: I have read the Software License and I agree to the terms.
     D: Display the Software License so I can read it now.
     Q: Quit.  Do not install OP-Crypt.

     Select A, D or Q:

To accept the terms of the Software License, type a.

5.4. Network key

     The encryption files for each network get personalized using the
network key.  Each network chooses its own network key, which should be
kept strictly secret.  Since the network key is central to the security of
the entire network it is absolutely essential that you choose a strong
network key.  Read the chapter on keys before making this important

     Please enter the OP-Crypt network key.  The network key may be up
     to 126 characters long.  The network key is case-sensitive, so
     abcd and ABCD are not equivalent.  All characters count,
     including blanks.

     Network key:

The network key must be typed exactly.

     To verify that the network key is correct, check the verification
code.  The verification code should be distributed along with the network
key to all of the stations in the network.  For example, 

     The verification code is 1234

     Is this correct?  (Y or N):

Type Y if it is correct, N if it is not.

5.5. Master key

     The master key is used for encrypting the OP-Crypt files on your hard
disk.  This protects you in case somebody copies your hard disk, or even
takes your entire computer.  Without the master key they cannot read your
encryption files, and without your encryption files they cannot read your

     Each station chooses its own master key.  It is essential that every
station picks a strong master key.  If even one station in a network used a
weak master key, that would endanger the privacy of every message to and
from every station that was using the same network key.  This is truly a
case where the weakest link breaks the chain.

     Unlike all of the other keys and passwords used by OP-Crypt, which are
typed only once, the master key must be typed each time you start OP-Crypt.
You need a master key that is both strong and easy to remember.  Be sure to
read the chapter on keys before choosing your master key.  Enter the master
key at the prompt 

     The Master Key is required for running OP-Crypt.
     The Master Key is case-sensitive.  For example, the 6 words
        sample   Sample   SAMple
        SAMPLE   SamPle   SamplE
     are all considered different keys.  All characters are taken
     as part of the key, including leading and trailing blanks.

     Please enter the Master Key.

Type your master key exactly and then press Enter.

5.6. Completing the installation

     The rest of the installation is done automatically by OP-Crypt.  It
takes some time to personalize the encryption files and write them to your
hard disk.  The program will display 

     Installing the OP-Crypt files ...

Do not interrupt the program during the remainder of the installation

     When the installation is complete, OP-Crypt will automatically start
your first session.  It is a good idea to verify the installation by
encrypting and then decrypting a sample message.  Once you are satisfied
that the program has been installed correctly it is strongly recommended
that you back up your hard disk.


     Choosing the keys for encrypting your files is one of the most
critical steps in using the OP-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.

6.1. 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.

6.2. 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 digits = 3.3 bits
     Single case letters = 4.7 bits
     Mixed case letters = 5.7 bits
     Mixed letters and digits = 5.9 bits
     Mixed letters, digits and 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.

6.3. 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 letters 


     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

6.4. 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
artificial 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 increases the strength of your

     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

     Wise king Haplico "Lion 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 crivan

     lobykar elb dixiat glem urbiqeo dhorsh uz vilagump

6.5. 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.

6.6. 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.

     Keys should never be written or pasted on the computer itself, the
computer desk, a desk pad or calendar, the cover of a notebook or steno
pad, the bottom of a stapler, telephone or flowerpot, the back of a
clipboard, letter tray or desk organizer, or any similar place.  Intruders
know to look in such places.  Don't make their job easy.

6.7. 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 total
strength of 77 bits.  Because of the LLDDD pattern 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.

                         Desired 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 you would read across the top row
of this table.  If you wanted the decimal key to have a strength of 125
bits, you would look at the second column in the top row to find that 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 OP-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.)

6.8. 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 OP-Crypt asks for it.

Appendix A. DOS BASICS

     OP-Crypt runs under DOS, not under Windows.  DOS was the primary
operating system for personal computers from about 1975 to 1995.  Older
versions of Windows, prior to the introduction of Windows 95, ran as tasks
under DOS.  Since 1995 the situation has reversed, and DOS now runs as a
task under Windows.  Every computer user before 1995 knew DOS well.
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.  If there
is a DOS icon on your desktop or in a taskbar, you can skip the rest of
this section.

     If there is no DOS icon on your desktop or taskbar you may find one
elsewhere.  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.  You just need to search
deeper.  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 DOS 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 top 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 makes 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 later 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. Long names

     Some Windows files and directories have long names, or names
containing blanks or dots, such as

     Documents and Settings
     My Music

Microsoft has made the naming of files and directories incompatible between
Windows and DOS.  DOS limits directory names to 8 characters, and does not
allow blanks in names.

     To refer to these directories, you need to shorten the names down to 8
characters.  The short name is formed by taking the first 6 non-blank
characters of the name plus the combination ~1.  When the name of a
directory contains a . dot character, each of the parts of the name is
treated separately.  For example, for the directories above,

     Documents and Settings   would be called   Docume~1
     My Music                 would be called   MyMusi~1
     Microsoft.Net            would be called   Micros~1.Net
     SharedReg12.dll          would be called   Shared~1.dll

Thus a full path and file name such as


in DOS would be called


     It is a good idea to give all of your own files and directories names
that are compatible with DOS.  The names should be no more than 8
characters long and should not contain blanks.

A.8. File operations

     Besides the encryption and decryption operations that you perform
using OP-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.

A.9. Batch files

     Batch files are a useful way to reduce the number and complexity of
the DOS commands that you must type.  Each batch file can contain any
number of DOS commands.  You execute the entire sequence of DOS commands
just by typing the name of the batch file.

     Here is a simple example.  Suppose that you frequently use the program
OP-Crypt.  If the current directory is \plans\tower but OP-Crypt is in the
directory \programs\download then to use OP-Crypt you would type


To make this easier, you could create a batch file named OP.bat on the
current directory.  This file would contain the single line


Now when you wanted to execute OP-Crypt all you would need to type is


     You could place a copy of the batch file OP.bat in every directory
where you usually work.  Then you could run OP-Crypt from anywhere just by
typing OP.  You would not need to have multiple copies of OP-Crypt.

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

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© Copyright 2005-2012 Frank Rubin
All rights reserved. No part of this manual may be reproduced in any form without the express permission of the author.