MD5 Hash - What is this?

Hi!

What is MD5 Hask. How can I find MD5 for a file?

Thank you in advance

Adsayaa
AdsayaaAsked:
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AultoCommented:
criptology (or something like this)
used for make (normally) systems more safe

example
imagine you do have a database with many users informations.
if someone exploit this system, he may see all the content of this database, including users passwords and emails. if this password is cryptographed in md5, he won't know what is the pass.

anyway, there ways to pass by this. like bruteforce(many combinations for finding the real string), rainbowtable (i think thats the name, its a table [normally in database] with many combinations of md5 hashes, so, the hacker may find the encrypted password in only one query)

see how it works (on login systems):

sign up:
login-name: aulto
password: aulto123

in the database, it will be:
login-name: ault
password: somemd5hash (course its not so)

in the verification:

input: aulto, aulto123
it will crypt the aulto123 and search in database for aulto,somemd5hash.

i have not too many time for explaining it better.
but i think you'll can understand
cya
[]'s
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JohnBusiness Consultant (Owner)Commented:
From the perspective of a file, a number of sites / vendors provide MD5 hash details for the file you want to download. For example, VMware Workstation 7 is over 1/2 Gb to download. You want to know that the download was correct. You run DigestIt on the download, input the MD5 has, and DigestIt verifies the file.

DigestIt is readily available as a free download and comes in 32-bit and 64-bit versions.

... Thinkpads_User
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yasserdCommented:
Simply, a hash (SHA1, MD5..etc) is a fixed length string. It is produced when a specific operation is done on a file to calculate its hash. The hash is used to ensure the integrity of a file. So, if hashes are calculated for two files having identical contents except the second file has just . (dot) at the end, they would have different hashes.

For more info:http://en.wikipedia.org/wiki/Cryptographic_hash_function

You can get a hash (MD5) calculator here: http://code.google.com/p/jdigest/
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slemmesmiCommented:
Dear Adsayaa,

Check out Microsoft's "Availability and description of the File Checksum Integrity Verifier utility" article about FCIV, which is a great/free to for calculating MD6, SHA etc.: http://support.microsoft.com/kb/841290

I use the tool for calculating checksums, to ensure integrity of files.

Kind reagrds,
Soren
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Rich RumbleSecurity SamuraiCommented:
File names have no bearing on the hash, but the rest of the above is correct. Renaming and or copying a file will result in the same hash for that file(s). An MD5 hash is a one-way operation, meaning that given the hash, one could never "reverse" it and recreate the original source. Brute force can be used, where you attempt to use plain-text files or strings, pass them through MD5 and see if they match.
For example. abcd = E2FC714C4727EE9395F324CD2E7F331F in MD5... there is no other way to make "E2FC714C4727EE9395F324CD2E7F331F" back into abcd... one has to type "abcd" and hash it to see they match. With files brute-force is much much harder... so the MD5 hash of the file can tell you if the file you have has been messed with by comparing the hash the author publishes with the hash you derive from your download. If one small thing changes inside a file, a extra space, changing the case of one single letter, the hash changes completely.
-rich
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