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WinCRC Cyclical Redundancy Code Generator for Windows Version 1.0 Eric Roe 3137 Briarcliff Avenue Vestal, New York 13850 Copyright (c) 1994 INTRODUCTION Welcome to WinCRC version 1.0. WinCRC can generate many of the most popular CRCs, checksums, and message digests for your files. This information can be written to a special 'key file', so you can verify your files at a later time. "What exactly is a CRC?", you might ask. CRCs or Cyclical Redundancy Codes are a popular method of error control for digital data -- like a file on your PC. A CRC generator takes as input a stream of digital data, does some mathematical footwork on the data, and outputs a number called (amazingly) the CRC. This number, which is usually 16 or 32 bits in length, can be used to detect any errors which might occur (or be introduced) into the original data. How? WinCRC does it by comparison. Say you want to verify that a certain file has not been corrupted. If you had generated a CRC for the file at an earlier date, you could simply generate a CRC for the same file again -- making sure you used the same CRC method. If the two CRCs are identical, the file is most likely intact. I say 'most likely' because there is always a possibility, usually extremely remote, that an error is not detected. This method of comparing two CRCs also works with checksums and message digests. Checksums and message digests are also used for error detection. Checksums are quite fast but are not terribly robust. As their name implies, they are the sum of each byte of the input data. Since it's easy to get several different numbers to add to the same sum, checksums can be fooled with very little effort. Message digests, at 128 bits in length, are extremely secure. It has been theorized that it is not computationally possible to generate two files that will have the same message digest. This security does come at a cost -- it's more time consuming to generate a message digest than a CRC or checksum. "OK, so what good does it do me?" A good question. Any time you move data around there's a chance of an error creeping in. Most telecommunication software has some form of built-in error detection. That way if there's a glitch when you're downloading or uploading a file, the software can re-send the part that got messed up. The same thing can happen when you move a lot of data around on your PC. A very good example is a hard disk defragmenting program. On a large drive, hundreds of megabytes might be swapped about. If a single bit in your favorite game gets inverted... POOF! it might not work. Or, what happens if there's a power loss when defragmenting? Which, if any, files might be corrupted? There's the magic of WinCRC. Use WinCRC to generate a key file for any files you're concerned about. Then do the defragmentation, tape backup, or whatever other operation you need to do to your files or disk. Now when the defrag program is done or you've restored from tape, use WinCRC to do a file verification. Any files whose CRCs have changed will be flagged and their name and error recorded. You can easily pinpoint any erroneous files and deal with them. If a particular package has been zapped, you only have to re-install it and not worry "Maybe something else is messed up too." It saves a lot of time if you only have to re-install one package, rather than everything on the drive just to get peace of mind. WinCRC version 1.0 can generate the following 16 bit CRCs: CRC-16 CRC-CCITT SDLC IBM CRC-16 Reverse CRC-CCITT Reverse SLDC Reverse IBM Reverse LHA ARC Zoo LRCC-16 and these 32 bit CRCs: CRC-32 ETHERNET ZModem PK-Zip ARJ It can also generate the following checksums (the number indicates how many bits wide it is): Checksum 8 Checksum 16 Checksum 32 and these 128 bit Message Digests: MD4 MD5 (experimental; see note) ** Note that many of these are actually the same CRC but with different names. See ALIASES for more information. USING WINCRC SELECTING A KEY FILE WinCRC is most useful when you are using a Key File. When generating CRCs, WinCRC can write the filename, path, and CRC to the key file. This same key file can be used to verify the files. When WinCRC starts, no key file is selected and '<none>' is shown for the key file. Press the 'KEY FILE' button and the Select Key File dialog will pop up. By default, files with the extension .KEY are shown. You can type a new search spec and click 'OK' or hit <RETURN> and whatever spec you entered will become the new default for this session. Select an existing key file or type a name in the Filename edit control. If the file exists, it will become the selected key file. If not, you are prompted as to whether or not you want the file created. Select 'YES' to have the file created or 'NO' to return to the Select Key File dialog. Note that the file is NOT created until you actually do a generate. Once you have selected a key file, you must check the 'Use Key File' check box to actually use the file. The Verify option requires you select a key file and check the Use Key File option before it becomes available. WinCRC tests the selected key file to make sure it's valid. If you're generating CRCs and the key file does not yet exist, it is created. If the file exists, but is not a WinCRC key file, CRC generation or verification will not continue. Key files are standard ASCII files and can be viewed by most editors including Windows Notepad, MS-DOS Edit, and DRDOS Editor. GENERATING You can Generate CRCs for files with or without a key file. If you don't use a key file, the CRC for each file is generated and you can choose to do the next file or to quit. The CRC is shown on the 'Message:' line of the Generating dialog box. When using a key file, the CRC is not shown. Before generating any CRCs you'll need to select some files and also what method you're going to use. The current CRC method is indicated in the 'Method' drop down combo box. After selecting what method to use you have to ways to select some files. You can use the Files listbox to select file individually, or the Include/Exclude edit controls to set up a 'File Inclusion Mask.' WinCRC can generate CRCs for all files that fit a given specification. The basic logic is to include any files that: have been selected in the file listbox, or those that match the Include specification but not an Exclude specification. The Include/Exclude controls use standard DOS wildcards and can contain multiple specifications separated by spaces. For example, to include all files with .COM and .EXE extensions type: '*.EXE *.COM' (don't type the single quotes) in the Include edit control. Remember to put a space between the two specs. Now if you click 'GENERATE', CRCs for all .EXE and .COM files will be generated. If you want to Exclude any files that start with the letter 'A' or 'B', just enter 'A*.* B*.*' in the Exclude line. Now you'll get all .EXE and .COM files that don't begin with either A or B. Since files selected in the Files listbox are always included, you can override the Include/Exclude specifications for the directory WinCRC is currently in. If you're using a key file, right after you click 'GENERATE', you will be presented with the Generate Options dialog box. This dialog contains two check boxes. You can select to overwrite an existing key file and/or to record only file (no path) information in the key file. Recording only file info is useful if you're moving a group of files and don't know if they'll have the same path specification. The file SAMPLE.KEY included with this package was generated without path info in the key file. Note that because no path info is recorded it's not very useful to check Include Subdirectories; you'll just end up with alot of File Not Found errors when you do a Verify. VERIFYING To verify files, you must have selected a key file. Check the Use Key File check box and the 'VERIFY' button will become active. When you press 'VERIFY', CRCs for all files in the key file are generated and then compared to the stored values. If the CRCs don't match or a file can't be found, the error is printed on the 'Message:' line in the Verifying dialog. The file in error and the error message is also written to a file named WINCRC.ERR. Like key files, WINCRC.ERR is a standard ASCII file. Each time you use Verify, WINCRC.ERR is overwritten. WINCRC.ERR is located in the working directory for WinCRC. You can change the working directory by using the Program Manager. During verification, WinCRC will stop when it encounters an error. You can press 'NEXT' which continues but will stop with the next error, or you can press 'FINISH' which continues without stopping until all files have been verified. It you use the Finish option, you can always look in WINCRC.ERR to check on any verification errors. When using Verify with a key file that includes file names but no path information, you must be in the directory that contains the files to be verified otherwise WinCRC won't be able to find the files. There is one thing to note when using CRCs to verify files. Many programs maintain configuration files. SYSTEM.INI is an example of one of Microsoft Window's config files. Some programs actually write configuration information to their executable rather than in a separate file. Of course if the file changes, so does the CRC. In these cases, the file has not been corrupted, rather the user has changed one or more of the program's options. To avoid having WinCRC flag these files, make your changes BEFORE, using WinCRC to generate CRCs. CHOOSING A DEFAULT METHOD When you first run WinCRC, the default method is Checksum 8. WinCRC can maintain a different default method in the file WINCRC.INI. To choose a new default method choose 'DEFAULT', select whichever method you want, and click 'OK'. Next time you run WinCRC, the method you selected will be the current one. Note that choosing a new default method does not alter the current method selected for this session. ALIASES A number of the methods WinCRC uses are known by several different names. The table below shows the alternate names. Method Alias -------------------------------------------------- CRC-16 ARC, LHA, Zoo CRC-32 ETHERNET ZModem PK-Zip, ARJ CRC-CCITT SDLC, IBM CRC-CCITT Reverse SDLC Reverse, IBM Reverse Do not confuse CRC-32 with PK-Zip or ARJ. PK-Zip and ARJ precondition the CRC before and after generation. CRC-32 does not. If you use CRC-32 you won't get the same CRC values that PK-Zip or ARJ generate. KEYBOARD USERS If you're using a keyboard rather than a mouse, all of the Window's controls respond in their default fashion. I.e. to "press" a button, tab to it and then press the space bar. The one exception it the Directories list box on the main window. Since there is no button to switch to another directory, this list box uses the <RETURN> key. Hightlight the directory you want (using the arrow keys or spacebar) and then press <RETURN>. WinCRC will switch to the new directory. A NOTE ON MD5 As of version 1.0 of WinCRC, I am considering my implementation of the Message Digest 5 algorithm experimental. Although the algorithm is similar to MD4, I didn't have any other working code to verify the MD5 results that WinCRC generates. If you're not getting the MD5 output that you expected, this is probably the reason. REGISTRATION WinCRC is not a free or public domain program. You may use it for a period of thirty (30) days for evaluation purposes. To continue using it after that, you must register the software. The more people who register, the more incentive I have to update the program and implement user suggestions. Makes sense, huh? To register, send a check or money order for US $15.00, payable to Eric Roe, to the following address: Eric Roe WinCRC Registration 3137 Briarcliff Avenue Vestal, New York 13850-2859 Also, if you have any comments and/or suggestions on how I can improve WinCRC you can send them to me at the above address. I can also be reached via e-mail at: ericroe@aol.com. DISTRIBUTION WINCRC.EXE and associated help files and documentation are Copyright (c) 1994 by Eric Roe, all rights reserved. They may not be distributed in an incomplete or modified form, nor can they be sold for profit without prior written consent of the author. If this software is to be distributed it must be distributed as a package consisting of the following files: WINCRC.EXE WINCRC.HLP WINCRC.DOC WINCRC.ERR SAMPLE.KEY REGISTER.DOC README.1ST Software dealers and shareware libraries may charge a minimal copying/disk fee for the above package not to exceed US $8.00. DISCLAIMER This software, WINCRC.EXE and its associated documentation and help files, is provided on an "as is" basis without warranty of any kind, express or implied, including, but not limited to, implied warranties of merchantability, fitness for a particular purpose, functionality, data integrity, or data protection. Persons using this software bear all risk as to the quality and performance of the software. The author will not be liable for direct or indirect damages or data loss, even if the author was informed of the possibility of such damages or data loss. Suggestions, improvements, diagrams, and other documents or documentation sent to the author become property of the author. No reimbursements or remuneration will be made.