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Old 2 weeks ago
  #541
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monomer's Avatar
 

Quote:
Originally Posted by hugol View Post
You're correct - it's a hash - which means absolutely there will be collisions (different inputs that result in the same hash).

However these collisions are extremely unlikely / hard to find.
Yes, i stated that already.
I just noted that a hash is not a proof of identicality.
Old 2 weeks ago
  #542
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monomer's Avatar
 

Quote:
Originally Posted by hugol View Post
Also see this answer around how hash functions are designed to both detect single byte differences between files - but also specifically guard against collisions occurring for minor differences. https://askubuntu.com/questions/8348...e-same-md5-sum.

"MD5, like any hashing algorithm, was deliberately designed so that a collision won't happen if you just change a handful of characters. You have to change most if not all of them in order to cycle back around to the same hash. That's because the whole point of a hash is to detect single-bit (or few-bit) errors; in this problem domain, you want the smaller changes to definitely trigger a hash change. Flawed though we now know MD5 to be, that property holds to this day."
I don't want to spoil the party, but a little further down from the quote you posted was this:

Quote:
There is one caveat, though: An md5 sum is 128 bits (16 bytes). Since the number of different possible file contents is infinite, and the number of different possible md5 sums is finite, there is a possibility (though small probability in most cases) of collision of hashes. In other words, two different files can produce the same sum when hashed with md5.

Because of this, it's better in some cases to use a higher bit hash (more possible different outputs), to reduce the (already low) probability of an accidental hash collision, and increase the difficulty of creating a deliberate hash collision through brute force.


Anyway, i was just pointing out that a hash is not a proof of there being or not being a change.
Old 2 weeks ago
  #543
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monomer's Avatar
 

Quote:
Originally Posted by psycho_monkey View Post
I did exactly that.

They are.
I never doubted you.
I mean, this whole thread is silly anyway and we all know it, right?
Right guys?
Old 2 weeks ago
  #544
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hugol's Avatar
 

Quote:
Originally Posted by monomer View Post
I don't want to spoil the party, but a little further down from the quote you posted was this:
...
Anyway, i was just pointing out that a hash is not a proof of there being or not being a change.

My friend - I think we're in virulent agreement. I was quite specific in what I wrote. Absolutely it's is theoretically perfectly feasible that you will find different files that generate the same exact hashcode - that's the nature of hashing algorithms.

However in practical terms - the likelihood you could even identify 2 different files that gave the same exact hashcode - is very very very low. Further to this, the likelihood that corruption on a file up/downloaded online (or even if that file were deliberately re-encoded) could lead to the changed version having the same exact hashcode as the original, is so incredibly unlikely, in practical terms it just won't happen. That's why we are saying it's ok to determine if a file has been changed by using a hashcode.

And yes - even with a fairly ****ty hashing algorithm like MD5 - but mostly we use SHA256 nowadays.
Old 2 weeks ago
  #545
Gear Guru
 

Quote:
Originally Posted by hugol View Post
My friend - I think we're in virulent agreement.
A very topical misspelling?

Wish there was a topical treatment.
Old 2 weeks ago
  #546
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Quote:
Originally Posted by mattiasnyc View Post
A very topical misspelling?

Wish there was a topical treatment.
Good point what was I thinking.... Violent agreement..... damn it Coronavirus overload clearly. I'm committing myself to 14 days isolation immediately.
Old 2 weeks ago
  #547
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hugol's Avatar
 

Quote:
Originally Posted by monomer View Post
I never doubted you.
I mean, this whole thread is silly anyway and we all know it, right?
Right guys?
Amen to that brother! However perversely whilst some of the discussions on this forum remain sane/well reasoned/polite/informative - it's the bat**** crazy stuff like this that draws us in and has people following/responding to complete nonsense at all hours (despite better judgement).....
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