Richter, Miller & Finn is pleased to provide the following information about using ARJ and PKZIP for low level encryption.

• The ARJ and PKZIP Compression and Archiving Software;
• How to Use This Software for Low Level Encryption Purposes; and
• How to Download the Necessary Files Using Your Web Browser.

ARJ and PKZIP are two well known and widely used file compression and archiving software programs which are available in shareware versions for non-commercial use. Each program is also available at modest cost for commercial use. ARJ is available at or through the ARJ web site. PKZIP is available at or through the PKZIP web site.

The most common use of ARJ or PKZIP is to take a group of uncompressed files, and produce a single compressed archive file containing all of the uncompressed files. Any one or more of the uncompressed files can be later extracted from the single compressed archive file and recovered in a lossless manner -- in exactly the same form that it had prior to compression. ARJ and PKZIP are both commonly used to compress files before storage so that the storage requirement is reduced. In the case of word processor or text files, for example, compression ratios of two or three to one are commonly realized, thereby reducing the storage volume requirement.

The developers of the current versions of ARJ and PKZIP have both "built in" a "password" feature so that if files are compressed into a single archive file with the use of a user provided "password", the original files cannot later be recovered (i.e. extracted) unless the same "password" is used when the files are being extracted.

These "password" features of ARJ and PKZIP work reasonably well and are more than sufficient to deter many or most casual on-lookers or hackers; however, neither system is cryptographically secure. Thus, we refer to the ARJ and PKZIP types of encryption as low level because it is insecure against an "attack" by someone who is modestly informed about cryptographic techniques and the particular encryption algorithms used by those programs.

Nevertheless, the low level encryption capabilities provided by ARJ or PKZIP may be put to good use in situations in which there is no reason to believe or suspect that encrypted files, if intercepted, would be subjected to a determined or sophisticated cryptographic attack. For such situations or where the content of the files have only limited potential for misuse, perhaps only for a limited period of time, such low level encryption may be suitable. You should be aware that plain text files encrypted using the one-step encryption options provided by ARJ and PKZIP can be successfully decrypted in only a few minutes by a determined intercepter with only a modest level of technical sophistocation.

The basic communications security considerations which favor the use of the high level encryption in certain other situations -- such as can be provided by the PGP software -- are discussed elsewhere on these WWW pages. The use of high level encryption which is cryptographically secure requires a somewhat more technically sophisticated user.

We now provide a brief explanation of how to use the ARJ and PKZIP software to implement low level encryption systems. As will be seen, this is very easy to do. Please note that we are describing two completely separate systems, one which uses ARJ and the other which uses PKZIP. Both are similar at a functional level, but are not compatible with one another. All necessary files are available from our Anonymous FTP Server.

The ARJ low level encryption system which we describe requires three separate files: arj.exe, arjdecry.bat and arjencry.bat , each of which is available from our Anonymous FTP Server. Each of the DOS batch files, arjdecry.bat and arjencry.bat contain descriptions of how to use them. Similarly, arj.exe contains "help" screens.

   1. First, create a new subdirectory on your hard drive to 
      be used as a working directory.  For example, enter
      
           MD C:\LLCRYPTO      
 
      at a DOS command prompt to create a new directory  \LLCRYPTO. 

   2. Copy each of the files, ARJ.EXE, ARJENCRY.BAT and ARJDECRY.BAT
      into the newly created working directory.  
      
   3. From now on copy any files you wish to encrypt into that working
      directory.  For example, if your have two word processor files,
      AAAA.DOC and BBBB.DOC in you \WINWORD directory, copy those files
      into the \LLCRYPTO directory in preparation for encyption.
      
   4. Assume we wish now to compress and encrypt all *.DOC files in the
      working directory into a single, compressed archive file to be
      named WORDDOCS.ARJ.  (You can select any DOS permitted filename
      you wish for this file.)  Next, choose a Password to be used for 
      both encryption and decryption.  Remember to write down or save the
      Password.  You or whomever you send the WORDDOCS.ARJ file to will
      need to know the Password in order to decrypt and extract the 
      original document files.  Assume, that you choose AbCdEfG123 as 
      your Password.  (You can choose almost any password you want.)
      
   5. To compress and encrypt all *.DOC files into an *.ARJ file named
      WORDDOCS.ARJ using the Password: AbCdEfG123 , you will use the
      ARJENCRY.BAT file.  To do this, simple enter the following at 
      the DOS command prompt while in the \LLCRYPTO working directory:
      
           ARJENCRY WORDDOCS *.DOC AbCdEfG123    

      The encrypted file WORDDOCS.ARJ will be automatically created in 
      your working directory \LLCRYPTO .
      
   6. To decrypt and extract the files is equally easy.  Assume you 
      have received an *.ARJ file named WORDDOCS.ARJ and you are told
      that the Password is: AbCdEfG123 .  You will first need to copy
      the WORDDOCS.ARJ file into your working directory:  \LLCRYPTO .
      Then simply enter the following at the DOS command prompt while
      in the working directory  \LLCRYPTO :
      
            ARJDECRY WORDDOCS AbCdEfG123    
	    
      The *.DOC files in WORDDOCS.ARJ will then automatically be decrypted
      and extracted into your working directory, \LLCRYPTO .

That all there is to it! Easy?

The PKZIP low level encryption system which we describe requires three separate files: pkzip.exe, pkunzip.exe, zipencry.bat and zipdecry.bat , each of which is available from our Anonymous FTP Server. Each of the DOS batch files, zipdecry.bat and zipencry.bat, contain descriptions of how to use them. Similarly, pkzip.exe and pkunzip.exe contains "help" screens.

   1. First, create a new subdirectory on your hard drive to 
      be used as a working directory.  For example, enter
      
           MD C:\LLCRYPTO      
 
      at a DOS command prompt to create a new directory  \LLCRYPTO. 

   2. Copy each of the files, PKZIP.EXE, PKUNZIP.EXE, ZIPENCRY.BAT 
      and ZIPDECRY.BAT into the newly created working directory.  
      
   3. From now on copy any files you wish to encrypt into that working
      directory.  For example, if your have two word processor files,
      AAAA.DOC and BBBB.DOC in you \WINWORD directory, copy those files
      into the \LLCRYPTO directory in preparation for encyption.
      
   4. Assume we wish now to compress and encrypt all *.DOC files in the
      working directory into a single, compressed archive file to be
      named WORDDOCS.ZIP.  (You can select any DOS permitted filename
      you wish for this file.)  Next, choose a Password to be used for 
      both encryption and decryption.  Remember to write down or save the
      Password.  You or whomever you send the WORDDOCS.ZIP file to will
      need to know the Password in order to decrypt and extract the 
      original document files.  Assume, that you choose AbCdEfG123 as 
      your Password.  (You can choose almost any password you want.)
      
   5. To compress and encrypt all *.DOC files into an *.ZIP file named
      WORDDOCS.ZIP using the Password: AbCdEfG123 , you will use the
      ZIPENCRY.BAT file.  To do this, simple enter the following at 
      the DOS command prompt while in the \LLCRYPTO working directory:
      
           ZIPENCRY WORDDOCS *.DOC AbCdEfG123    

      The encrypted file WORDDOCS.ZIP will be automatically created in
      your working directory, \LLCRYPTO .
      
   6. To decrypt and extract the files is equally easy.  Assume you 
      have received an *.ZIP file named WORDDOCS.ZIP and you are told
      that the Password is: AbCdEfG123 .  You will first need to copy
      the WORDDOCS.ARJ file into your working directory:  \LLCRYPTO .
      Then simply enter the following at the DOS command prompt while
      in the working directory  \LLCRYPTO :
      
            ZIPDECRY WORDDOCS AbCdEfG123    
	    
      The *.DOC files in WORDDOCS.ZIP will then automatically be decrypted
      and extracted into your working directory, \LLCRYPTO .

That all there is to it! Easy?

This WWW Server contains the pertinent files for implementing low level encryption and decryption systems with ARJ and PKZIP using the files described above. Before attempting to download these files, set your Web Browser to save the files to your harddisk.

      For the ARJ system, you need to download the following three separate 
      files from this WWW Server using your Web Browser:
      
                   ARJ.EXE
		   ARJENCRY.BAT
		   ARJDECRY.BAT
      
      Click on each filename to automatically connect to and download 
      the necessary files using your Web Browser.
      
      ******************************************************************
      
      For the PKZIP system, you need to get the following four separate
      files from the Anonymous FTP Server:
      
                   PKZIP.EXE
		   PKUNZIP.EXE
		   ZIPENCRY.BAT
		   ZIPDECRY.BAT
       
      Click on each filename to automatically connect to and download 
      the necessary files using your Web Browser.