Adding to PowerIT post. MD5 (message digest) and SHA are hashing algorithms. They take a variable length input (your data content such as a file) and produce a fixed lenght output. The output is not big enough for you reverse the process.... the main purpose of hash is integrity.
As PowerIT posted, it's similar to checksum.... so let's use checkdigit (since most of us know checkdigit) in the following example - we use mod 9 checkdigit. Using modulus 8, the check digit 3 can be arrived from any of the following number strings as input - 11, 19, 27, 123, 131, 139 and many more ........
Even if you know it's modulus 8 and the check digit is 3 - there is no way for you to tell which number string was the original input.
If you are looking for software to produce MD5 or SHA hash string for files - google them.
Gnart
Main Topics
Browse All Topics
by: PowerITPosted on 2007-06-23 at 08:36:10ID: 19348044
You can't. Because MD5 is not an encryption system but a cryptographic hash.
Look at it like a checksum. It's the hash of the total content of a document, password etc ...
This is a mathematical one-way operation, you can not 'decrypt' it.
The only thing you can do is rehash a document and see if it has not changed, because the supplied hash should be the same with the one you recalculate.
Another application is hashing password and store them. Here again passwords are never decrypted. A user enters a password and it's verified with the stored hash. This is a way to store passwords without making them readable. An attack against this exist using a table with precalculated hashes (called rainbow tables). In a way you could say that passwords could be decrypted this way, but this is actually a lookup.
J.