How to control the MD5 sum of an ISO image under Windows and under Linux

BitTorrent verifies the integrity of the downloaded ISO images but you can control this also with a specific program. This verification is necessary for security reasons if you have downloaded it via FTP.

Under Windows

When you are making your first steps of exploring GNU/Linux from Windows, you will do this in most cases like this :

• download an ISO image file via internet
• burn this ISO image on a DVD or on CDs

• to verify the md5 sum of the ISO image.

It is an algorithm which authentifies the conformity of an image in comparison to its original. It is an encryption key which confirms the integrity and unbrokenness the downloaded files.

As an example, take a look at the md5 file for the 3 first CDs of the Mandrakelinux10.0-Official Powerpack. It has the name of Mandrakelinux10.0-Official-Powerpack-CD1-3.md5. Its file extension is .md5.

bc6e7962bb41e970776630c251ae1ecc Mandrakelinux10.0-Official-Powerpack-CD1.i586.iso c24810323310f624a4af8abc3ab0e4ef Mandrakelinux10.0-Official-Powerpack-CD2.i586.iso 3090d1a07f6ab6f8f2989aece8bb4bd4 Mandrakelinux10.0-Official-Powerpack-CD3.i586.iso

Each md5 key consists of 32 alphanumeric characters:

bc6e7962bb41e970776630c251ae1ecc
c24810323310f624a4af8abc3ab0e4ef
3090d1a07f6ab6f8f2989aece8bb4bd4

You can use any text editor to view the .md5 file. Under Windows you can use Notepad, Word or OpenOffice.

2) Where to find this md5 sum ?

In most cases this file will be downloaded and available together with the ISO image. In few cases it is only displayed on the internet site from which you download this ISO image.

3) Why to verify the md5 sum ?

This allows you to be sure that the downloaded file is complete and it does not contain any virus or spy software nor a back door. If you do this check you can avoid later troubles and error messages because you only install a healthy and complete software.

Here an example among others how something could be destroyed : The download of the 3 CDs of Mandrakelinux 10.0 Community via eMule has contained the 3 CDs and as a bonus the virus BAT.IBBM.Wavefunc.A which does destructive things under Windows.

Download an image from the internet site of the editor of the distribution or from one of its mirror sites to protect yourself against unfair pirates. And after this verify the integrity and unbrokenness of the image before you burn it.

4) How to easily verify this md5 sum ?

• fetch the programme md5summer from www.md5summer.org (you can also use wxChecksums, (works also under linux. Under Mandrakelinux you can get a RPM for this: download wxchecksums). After the installation it is sufficient to double-click on the MD5 file to get the answer : is your file good or not ?)
• start your usual antivirus program (normally someone isn't such carful)
• uncompress the archive .zip which contains md5summer.md5 and md5summer.exe
• you can execute the program from the folder where you have uncompressed it. If you want, then you can also copy it manually to the C:Program Files folder.

• retrouver l'icône de démarrage du logiciel md5summer.exe, la double-cliquer

Pour l'exemple, vérifions ensemble l'intégrité du logiciel md5summer.exe :

• double clic sur md5summer.exe

• choix du dossier contenant le fichier à vérifier :

• clic sur Verify sums (contrôler les sommes md5)

• choisir le fichier se terminant par .md5 et cliquer sur ouvrir

Comme il est visible en bas à gauche, il y a 4 états possibles :

• Unprocessed : non effectué
• OK / Done : OK / effectué
• Processing : en cours de vérification
• Error : erreur

Under Linux it is easy

You do not have to use a special tool if you use K3B for burning the DVDs, because it does the check for you. The following command allows you to control an ISO image. The file .md5 and the ISO image must be under the same directory.

$ md5sum -c Mandrakelinux_***_.md5

You can also use the following command :

$ md5sum votreImage.iso

You will immediately get a hexadecimal number. Compare if it corresponds to the one give to your file.

If they are the same you can burn it on your DVD !

Voici un exemple concret:

• Ouvrez un terminal (Konsole par exemple) et allez dans le répertoire où se trouvent les images ISO
• Copiez-y les fichiers .md5 si ils n'y sont pas déjà
• Contrôlez les sommes (cf.plus bas). Cela peut prendre quelques minutes, suivant votre système.
• Comparez les résultats avec le contenu des fichiers .md5

Afficher les sommes à contrôler :

$ cd /home/user1/~BitTorrent/Mandrakelinux10.0-Official-Powerpack-CD1-3
$ cat Mandrakelinux10.0-Official-Powerpack-CD1-3.md5

bc6e7962bb41e970776630c251ae1ecc  Mandrakelinux10.0-Official-Powerpack-CD1.i586.iso
c24810323310f624a4af8abc3ab0e4ef  Mandrakelinux10.0-Official-Powerpack-CD2.i586.iso
3090d1a07f6ab6f8f2989aece8bb4bd4  Mandrakelinux10.0-Official-Powerpack-CD3.i586.iso

$ md5sum Mandrakelinux10.0-Official-Powerpack-CD1.i586.iso

bc6e7962bb41e970776630c251ae1ecc  Mandrakelinux10.0-Official-Powerpack-CD1.i586.iso

md5sum Mandrakelinux10.0-Official-Powerpack-CD2.i586.iso
md5sum Mandrakelinux10.0-Official-Powerpack-CD3.i586.iso

Vous pouvez aussi utiliser K3B. En effet, lorsque vous choisissez de graver une image ISO, il vous donne la somme md5 … Vérifiez simplement si c'est correct.

Checksum

Mandrakelinux Community 10.1

04b3b992e84cec3db1e28000f403ed69  Mandrakelinux-10.1-Community-CD1.i586.iso
b5e6d5c910069f90d77747213fa50769  Mandrakelinux-10.1-Community-CD2.i586.iso
c790625c0dd5b4679f9b5df4bb57e222  Mandrakelinux-10.1-Community-CD3.i586.iso
9dffdf830e170a0175d3e53a6b84f2b2  Mandrakelinux-10.1-Community-CD4.i586.iso
63617e17674d6b4871b4aead77f3e33e  Mandrakelinux-10.1-Community-CD5.i586.iso

Mandrakelinux Official 10.1

132d0fea15e901f4ef7f1a9647a77d49  Mandrakelinux-10.1-Official-Powerpack-CD1.i586.iso
19d00e9fcbaad73e1b082b26f28695d1  Mandrakelinux-10.1-Official-Powerpack-CD2.i586.iso
85c08d954186531363e8533e107d8897  Mandrakelinux-10.1-Official-Powerpack-CD3.i586.iso
c06ecf43e722b37c90e4ba14a0b68302  Mandrakelinux-10.1-Official-Powerpack-CD4.i586.iso
efe85416a3f3d69e8b0931e7db604377  Mandrakelinux-10.1-Official-Powerpack-CD5.i586.iso
e72652acaeb21059a536d3d6fb8a3055  Mandrakelinux-10.1-Official-Powerpack-CD6.i586.iso

more infos : Verify the integrity of a file or of a CD-ROM

Author : ~BlueBeetle