Verification of MD5, CRC and WINDOWS original CD

Date: 2005-9-3 Posted by: zhouhjss

MD5, CRC and verification of WINDOWS original CD Verification

1. The purpose of verification. Generally speaking, we are used to determine whether the disc or image is an original copy (note: it is not to verify whether it is a copy of the original ISO file! Those with special requirements Except. )

2. Assuming that we know the MD5 value of the original CD ISO (of course the virtual image has different formats, not necessarily ISO) and the CRC value of the original disc. 3P!:l

3. Applicable scope, as far as the verification of the original WINDOWS version is concerned, MD5 can verify whether the image file we have is a copy of the original iso file (note: it is a file). If the MD5 value is different, it means it is not a copy of the source ISO. CRC can verify whether the image we have is an image of the original disc (note: not a file) or a copy. 67g

4. Problems with MD5: If we use different tools to make the original iso, will the md5 value still be the same? It's definitely different. Use crc to verify again, the values ??must be the same. Because MD5 is a verification file, and CRC verification is a disc. In other words, there can be many image files with different MD5 values ??circulating on the Internet that are also original images, but the CRC values ??are all the same. Also, MD5 cannot be used to verify discs.

5. Suggestion: Use CRC to check whether it is an original copy or image. If you download a file, provide the downloader with an MD5 value, which can be used for verification (but this value is not necessarily related to whether it is the original image, and can only be used to verify whether there are any problems during the download process).

6. Questions about CRC verification

From the results, AutoCRC only says that this .ISO is valid (VALID). But it doesn't tell me whether the file I CRC is the same as other 505M .ISO files. In other words, as long as the ISO file is successfully mirrored from any optical disc to the hard disk, the CRC check will be correct, or VALID, right? .

Wrong!

A. When using cdimage to create a CD, you must add the -x parameter. Only after the creation is successful can it pass the crc check. If the original CD is modified, it will definitely fail (without re-adding crc verification). 1p|gG

B. After passing, you still need to check whether the specific values ??inside are consistent with the original version! L

MD5: The name of a message digest algorithm (also called one-way hash function). It uses a certain algorithm to finally generate a 128-bit check value (a 32-bit hexadecimal number) based on each bit of the source data. The most common application of MD5 is in cryptography. In this article, it is mainly used to verify file integrity. If you find the above text difficult to understand, you can simply think that MD5 is a 128-bit digital signature, used for verification. Just check whether the file has been modified.

CRC.EXE: CD media testing software. Microsoft added this verification information to the CD after win2000.