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DataCrypt INSTRUCTION MANUAL (C) COPYRIGHT 1984 ARTHUR MELNICK ALL RIGHTS RESERVED THIS PROGRAM IS USER-SUPPORTED SOFTWARE. IT MAY BE COPIED AND DISTRIBUTED FREELY, HOWEVER IT MAY NOT BE SOLD. IT IS COPYRIGHTED BY THE AUTHOR AND HE HOLDS ALL RIGHTS TO ITS DISTRIBUTION. IF YOU FIND THIS PROGRAM USEFUL, A DONATION OF $25 IS REQUESTED. SEND DONATIONS TO: ALMTEK P.O. BOX 6425 SAN RAFAEL, CA. 94903 FOR THOSE WHO WISH TO SEND A DONATION AND REQUIRE AN INVOICE FOR BUSINESS PURPOSES, ONE IS INCLUDED AT THE END OF THIS MANUAL. USERS SENDING THEIR NAME AND ADDRESS WILL RECEIVE ANY ADDITIONAL DOCUMENTATION AND/OR UPDATES PRODUCED. THIS SOFTWARE AND MANUAL ARE PROVIDED "AS IS" AND WITHOUT WARRANTIES AS TO PERFORMANCE OR MERCHANTABILITY OR ANY EXPRESS OR IMPLIED WARRANTIES WHATSOEVER. THE USER MUST ASSUME THE ENTIRE RISK OF USING THE PROGRAM. 1 DataCrypt (C) Copyright 1984 Arthur Melnick I. GENERAL DataCrypt is a general purpose cryptographic program used for encrypting and decrypting any type of file. It is designed to run on an IBM Personal Computer under the PC DOS operating system. Hardware requirements include 64K of memory, a monochrome or color display, and at least one disk drive, although two drives are recommended. Data is encrypted using a 40 digit key under a proprietary algorithm (formula). The program operates very quickly, requiring only about one second for each 1KB (1024 Bytes) of input. The input may be either the ciphertext or the unencrypted "plain text" and the opposite output is produced. II. DEFINITIONS The following terms will be used in this manual: <<<ALGORITHM>>> A mathematical rule or formula which is used to perform a specific calculation. <<<CIPHERTEXT>>> The encoded file. This is the seemingly random collection of bytes that yields the original file when decrypted under the same key used for encryptation. <<<DECRYPT>>> Convert ciphertext to plaintext. <<<ENCRYPT>>> Convert plaintext to ciphertext <<<PLAINTEXT>>> The file to be encrypted or the file which has been decrypted from the ciphertext. <<<KEY>>> The sequence of characters (usually a number) which is used by the algorithm that converts ciphertext to plaintext or vice versa. The same key must be used for both conversions for the operation to be successful. III. OPERATION To begin operation of DataCrypt, type "DATACR" at the system prompt. This will cause DOS to load and execute the file DATACR.COM. The program begins by displaying a menu. This menu will ask for one of the following choices: 1. ENCODE/DECODE A FILE 2. DELETE A FILE AND "UN-DELETE PROOF" IT 3. EXIT TO SYSTEM At the ENTER SELECTION: prompt, enter 1,2, or 3. If you do not enter one of the valid choices, a beep tone will sound and the prompt will reappear. The choices are explained in the following sections. 1 DataCrypt (C) Copyright 1984 Arthur Melnick 1. ENCODE/DECODE A FILE After option 1 is selected, the screen will clear and the following prompt will appear: ENTER INPUT FILE: _ The user must then enter a standard DOS filename. This file will be encrypted if it is a plaintext file or decrypted if it is a ciphertext file. If no drive is specified, the default drive is assumed. If no extension is input, it is assumed to be all blanks. Use of the global filename characters "*" and "?" is not allowed. If a global filename character is used or if the drive specified is not valid or if the filename input is not a valid DOS filename or if the file is not found on the specified drive, an error message is displayed and a beep tone will sound. The ENTER INPUT FILE: prompt will reappear. After the input file is specified, the screen will again clear and the following prompt will appear. ENTER OUTPUT FILE: _ PRESS RETURN TO OVERWRITE INPUT FILE The user must enter a standard DOS file name. This file will be the decrypted plaintext if the input is a ciphertext file or the encrypted ciphertext if the input is a plaintext file. If no drive is specified, the default drive is assumed. If no extension is specified, it is assumed to be all blanks. If no file name is specified, it is assumed to be the same as the <<<INPUT>>> file name. If only a return is input, the input file will be overwritten by the output file. The file length will not change if this done. <<<CAUTION!!>>> Entering the same filename for both input and output may damage the file. Use of the global filename characters "*" and "?" is not allowed. If a global filename character is used or if the drive specified is not valid or if the filename input is not a valid DOS filename or if it is not possible to either open an existing file of the specified name or create a new one, then an error message is displayed and a beep tone will sound. The ENTER OUTPUT FILE: prompt will reappear. If an existing file is specified as the output file, it is overwritten. If a new file is specified, it is created on the specified drive, provided there is room for another filename in the directory. After the output file is specified the following is displayed on the screen: 2 DataCrypt (C) Copyright 1984 Arthur Melnick ENTER A 40 DIGIT KEY (Use only the digits 0 thru 7) 1 5 6 10 11 15 16 20 . . . . . . . . . . . . . . . . . . . . _ 21 25 26 30 31 35 36 40 . . . . . . . . . . . . . . . . . . . . The user must now enter a 40 digit number to be used as an encryptation/decryptation key. Only the digits 0 thru 7 are allowed. If any other character is entered, the cursor will not move on to the next digit position and a beep tone will sound. The user may then reenter a valid digit. After all 40 digits have been entered, the following prompt appears: IS THE NUMBER ENTERED CORRECTLY? (Y/N) _ If the user answers "Y", the program goes on to processing the file. If the user answers "N", the following prompt appears: ENTER THE NUMBER OF THE DIGIT position TO CHANGE OR "*" IF THRU WITH CHANGES: _ The user may then enter any number in the range 1 thru 40. The cursor will then go to that digit position in the key and any valid key digit may be substituted for the one previously input there. The program will then repeat the prompt for another digit position. By this method any number of key digits may be changed. The process ends when a "*" character is input at which time the file will be processed. After a file has been processed and the program returns to the opening menu, option 1 may be selected again to process another file. When the key input screen appears for the second or subsequent time after DataCrypt has been loaded,an additional option is available to the user. At those times the key input screen contains the additional prompt: ENTER "S" FOR SEQUENTIAL MODE The letter "S" may be input in any digit position to invoke sequential mode. Sequential mode allows a file to be encrypted/decrypted under a key which is derived from the last key entered. Files encrypted in sequential mode MUST be decrypted in sequential mode IN THE SAME ORDER that they were encrypted. Sequential mode allows the user to encrypt a group of files without entering a key for each one and without USING THE SAME KEY TWICE. See section IV of this manual for a discussion of key selection in general and the inadvisability of using the 3 DataCrypt (C) Copyright 1984 Arthur Melnick same key twice in particular. After the key has been specified, the following is displayed on the screen: PROCESSING FILE This message will remain on the screen until the whole file has been encrypted/decrypted. At that time the opening menu will reappear. If at any time during the processing of the file there is no more room left on the medium used to hold the file, the following prompt appears: INSUFFICIENT ROOM ON DISK FOR OUTPUT FILE PRESS ENTER TO CONTINUE The partially processed output file will be deleted. When the user presses enter, the opening menu will appear. If sequential mode was being used, it is necessary to reprocess all files in the sequence after providing adequate disk space for the output files. 2. DELETE A FILE AND "UN-DELETE PROOF" IT The DOS operating system maintains a directory on each disk or diskette containing information about each file recorded on that disk. This information includes the name and extension of the file and on what particular tracks and sectors of the disk the file can be found. When a file is deleted, its entry in the directory is deleted and the sectors assigned to that file are "released" so that they may be overwritten by another file. Until those sectors are overwritten, however, they still contain the information recorded in the deleted file. Methods are available to recover that information even though the file directory entry has been deleted. (Actually, it is only necessary to change one byte in the directory to effectively delete an entry.) DataCrypt's option 2 prevents such information recovery by first overwriting the entire file with an alternate pattern of 1's and 0's before deleting the file entry from the directory. This option is useful when both the plaintext and ciphertext file reside on the same diskette and it desired to delete the plaintext without the danger of it being recovered. After option 2 is selected the screen will clear and the following prompt will appear: ENTER FILE TO DELETE: _ The user must then enter a standard DOS filename. This file will be deleted. If no drive is specified, the default drive is assumed. If no extension is input, it is assumed to be all blanks. Use of the global filename characters "*" and "?" is not allowed. If a global filename character is used or if the drive 4 DataCrypt (C) Copyright 1984 Arthur Melnick specified is not valid or if the filename input is not a valid DOS filename or if the file is not found on the specified drive, an error message is displayed and a beep tone will sound. The ENTER FILE TO DELETE: prompt will reappear. After the file is deleted, the opening menu will reappear. 3. EXIT TO SYSTEM Before the program terminates and returns to DOS, it first writes a pattern of 1's and 0's into those portions of memory that may contain sensitive information. Included are the disk transfer buffer, the key storage area, and certain sections of memory used for encryptation/decryptation calculations. This is done so that a subsequent user of the computer can not glean information by searching thru memory if the computer has not been booted since DataCrypt was last run. Entering selection 3 at the opening menu will clear the screen and produce the DOS system prompt. IV. KEY SELECTION The most important consideration in key selection aside from the obvious need to reveal the key only to those authorized to have access to the decrypted file is the requirement that no key be used more than once. This is because of the fact that cryptanalysis (code breaking) becomes a GREAT DEAL EASIER when the analyst is armed with two examples of ciphertext which have been encrypted with the same key. The analyst may not only be able to extract the plaintext from the ciphertext in these circumstances, but may also be able to derive the actual key itself. If the same key is used still again, the analyst can then decrypt the message with the same ease and speed as the intended recipient of the message! In choosing a key, the user should generally use a random pattern of digits. Try to avoid repeating the same digit a large number of times, and don't use a number known to a great many people, such as your telephone number. V. DATA COMMUNICATION CONSIDERATIONS DataCrypt can encrypt any type of file. This is because each byte of the input file can assume any of the 256 values possible to express with eight bits. Any input byte might be transposed to any of the 256 possible output bytes when operated on by the encryptation/decryptation algorithm. Because of this, any data communication software used to transmit a file encrypted by DataCrypt must operate in a mode which allows the transmission of "pure binary" files. In particular "7 bit" or "ASCII only" protocols will not work. 5 <<<INVOICE>>> <<<<<TO>>>>> ALMTEK P.O. BOX 6425 SAN RAFAEL, CA. 94903 1 ea. COPY DataCrypt CRYPTOGRAPHIC PROGRAM @ $25.00 <<<NET DUE>>>............$25.00 5.00