Newbie question about file hash values

[PC Hobbyist]

I've heard the term "hash" for years, but I never really bothered to try and understand until now. I've been reading some things online about it, but I'm curious if I have the right general idea.

Correctly if I'm wrong:

A hash is an algorithm that looks at a file's unique data information and produces a combination of numbers and letters that uniquely identifies that file. It can be used to confirm that the copy of the file you have is the original, unaltered version that the author created.


And here are a couple of questions:

1. So, if the file is altered in any way, it will have a new hash value? For example, every time I edit a picture or a Word document, the hash value changes?

2. Does every single file in my computer have a hash value?

3. How can I check what the hash value of a file is? What program can I use?

4. Are "hash", "checksum", and "hash checksum" the same thing?

5. Do programs that scan your computer for duplicate files, do so by looking at the hash value?


Thanks for helping me understand this a bit better (he-he no pun intended ).

 

[kimsland]

I've heard the term "hash" for years, but I never really bothered to try and understand until now. I've been reading some things online about it, but I'm curious if I have the right general idea.

Correctly if I'm wrong:

A hash is an algorithm that looks at a file's unique data information and produces a combination of numbers and letters that uniquely identifies that file. It can be used to confirm that the copy of the file you have is the original, unaltered version that the author created.
Yes

And here are a couple of questions:

1. So, if the file is altered in any way, it will have a new hash value? For example, every time I edit a picture or a Word document, the hash value changes?
Yes, it will increment by 1 ie OriginalHashValue+1
2. Does every single file in my computer have a hash value?
Yes
3. How can I check what the hash value of a file is? What program can I use?
>> http://www.beeblebrox.org/hashtab/HashTab Setup.exe
4. Are "hash", "checksum", and "hash checksum" the same thing?
There are different Hash codes (such as MD5, SHA1, SHA2, RipeMD, HAVAL and Whirlpool etc)
5. Do programs that scan your computer for duplicate files, do so by looking at the hash value?
Not always no, they usually just look at Filenames

Thanks for helping me understand this a bit better (he-he no pun intended ).

Answered in Red

 

[PC Hobbyist]

Answered in Red

Wow - awesome! Thanks! It's always a good feeling when you learn something new.

EDIT:
By the way, that HashTab shell extension is great! Really handy!

You know, I was playing around with it and I have a question. I had a .txt file and made a copy of it. Then I erased everything in the copy and wrote something else in its place. The two files should now be different, right? But when I compare their hash values, it says they are the same. Why is that?

 

[kimsland]

Did you check all the Hash values

 

[PC Hobbyist]

I must have been doing something wrong. I just tried it again and it worked fine. Even the most minimal change (like deleting a space in the txt file) will change the hash values like you would expect.

Thanks again.