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What exactly is the difference between an md5 and an iso. disadvantages and advantages of both?

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Md5 is a hash - iso is a disk image. –  Rich Bradshaw Feb 26 '10 at 23:59
    
An MD5 file is about 1KB and an ISO is about 700MB. –  Iain Feb 27 '10 at 0:31
    
Just imagine if we could reverse an md5, eh? :P –  Phoshi Feb 27 '10 at 0:37
    
@Phoshi: i'm not downloading that movie, i'm decompressing this hash. –  Ian Boyd Feb 27 '10 at 2:37
    
wonderful... sounds like I can "calculate" the ISO when I'm given only the MD5 –  netvope Apr 1 '10 at 20:59

2 Answers 2

up vote 7 down vote accepted

An MD5 is an 128bit hash value (such as 49f68a5c8493ec2c0bf489821c21fc3b), wheras an ISO file is a "disk image" - effectively a file containing the same data as a physical disk would. You're comparing the sticker on an apple to an orange, here - the two are not related. You may find ISO files that come with an MD5, as each file has a unique hash (Well, unique enough that it can be used for verification), and so a corrupt download (though not one tampered with--that is, it's valid to use MD5 for integrity checks, but not validation or security) will not return the same hash as the original file.

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It is misleading to mention MD5 as suitable for verifying the integrity (using the PKI definition), since it is broken. –  Janus Troelsen Apr 22 '13 at 17:51
    
@ysangkok: While this is undeniably true, and I would never advocate using MD5 for, well, anything at all in a new project, I feel it does still provide "good enough" verification to defend against data corruption. It's a hideously broken algorithm, true, but not so broken that it's very likely for random changes to retain the same hash. –  Phoshi Apr 22 '13 at 19:02
    
Yes, for checksumming it's great. But you specifically mentioned tampering. Which is the situation where you need exactly the security goal integrity, which MD5 does not provide since is it feasible to construct collisions. –  Janus Troelsen Apr 22 '13 at 19:40
    
@ysangkok: Oh, hm, so I do. I'm not sure that's a very defensible position at all. I'll edit the answer to make this clear. On the subject of checksumming, though, I discourage the use of MD5 there too--as it is, regardless of how broken, a cryptographic hash it is designed to be slower than a non-cryptographic hash, which can checksum data much faster with acceptable collisions. –  Phoshi Apr 23 '13 at 11:27

When you download disk images like iso there is *.md5 included!

The md5 is a hash of the related iso in order to verify its integrity! So when you download a disk image you compute $ md5 image.iso and compare what you get with the given md5 hash! If they match then your disk image probably doesn't have any errors!

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11  
You're the William Shatner of exclamation points. –  ceejayoz Feb 27 '10 at 2:48
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Either that or a 14-year-old girl. OMG!! –  Daniel R Hicks Apr 23 '13 at 11:49

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