As WhatIs.COM said {external link}, MD5 is the algorithm (developed by Professor Ronald L. Rivest of MIT) which is used to verify the data integrity through the creation of a 128-bit message digest from a data input (which may be a message of any length, even a file). This algorythm is claimed to be as unique to that specific data as a fingerprint to the specific individual. Here an integrity, in terms of data and network security, is the assurance that information can only be accessed or modified by those authorized to do so. There is a programme, MD5SUM.EXE, intended for the file digest calculation. It can be taken from TheOpenCD project {external link, 48kB} or from here {local link, 48kB}. It has to be placed on your computer, where the system environment variable $PATH is defined. Usually it is your system folder (c:\windows\command for Win95/98/ME or c:\winnt\system32 for NT/2K/XP). You can check where it is: find the icon “My Computer” on your “Desktop”, right click, “Properties” - “Additional” - “Environment Variables”. There you can find where your $PATH varible points. Alternatively, you can just put it in any place but, then, you will be able to run this program either from this directory, or using the whole path to this place e.g. d:\somedir\another\md5sum.exe.

It is well known, that for most DOS console programmes or applications the key /? exists, which in the most cases prints at the console some words about the programme purpose. This is not our case. The utility MD5SUM.EXE belong to the GNU utility set, which was designed mostly for UNIX environment. Some of such utilities, as MD5SUM.EXE, were ported to Windows environment, but inherit UNIX behaviour. If DOS application for sure has the key /? , then UNIX application may/will has the key –help, or –version, or -h, or, -v. In fact, when I find some unknown console application, I starting it and fitting a key for it - we’ll see what it gives. Even this is not so good - any time (most of time ) one have to know, what is he doing.

OK, anyhow, MD5SUM accepts –help and –version :

D:TMPmd5sum –help
Usage: md5sum.exe [OPTION] [FILE]…
or:  md5sum.exe [OPTION] –check [FILE]
Print or check MD5 checksums.
With no FILE, or when FILE is -, read standard input.

-b, –binary            read files in binary mode
-c, –check             check MD5 sums against given list

The following two options are useful only when verifying checksums:
   –status            don’t output anything, status code shows success
-w, –warn              warn about improperly formated MD5 checksum lines

   –help              display this help and exit
   –version           output version information and exit

The sums are computed as described in RFC 1321.  When checking, the input
should be a former output of this program.  The default mode is to print
a line with checksum, a character indicating type (`*’ for binary, ` ‘ for
text), and name for each FILE.

WARNING:  You are using a specially adapted copy of md5sum.  This version
       has been modified as follows:
       1) Only ever use binary mode
       2) Be more liberal about line endings in files used by –check
       3) Built-in Win32 file wildcard matching (globbing)
       This version was compiled by bruce@gridpoint.com for the
       People for a Clearer Phish.  Source code changes are available
       from Bruce upon request.

Report bugs to bruce@gridpoint.com

D:TMPmd5sum –help
md5sum (PCP patchlevel 2) (GNU textutils) 1.22

Usage:

– make the digest

D:pathmd5sum *txt
452babcf828a4dbd23c4f48b611fb2fa *file1.txt
0a78814b3a21b8ed84025ca2cd5df619 *file2.txt
9ee3f5af729a9c8b5e70741b5ffb2a82 *file3.txt

D:pathmd5sum *txt > digest.md5

D:pathmd5sum *txt –check digest.md5
file1.txt: OK
file2.txt: FAILED
file3.txt: OK
md5sum: WARNING: 1 of 3 computed checksums did NOT match

These digests are calculated for disk or diskette images, or files. Especially when we are talking about the public nets. First it is neccessary to download the file itself and then calculate the digest and compare with the original one. If the values are not equal to each other, then try to download again it or consider to drop it at all. In fact it is not so good idea to save the file and its digest …

@ Category Tech
<< Back