Decrypt hash string from String.GetHashCode?

Question

From this sample code from MSDN http://msdn.microsoft.com/en-us/library/system.string.gethashcode.aspx

The hash code for "abc" is: 536991770

But how to convert back the "536991770" to "abc"?

Answer 1

The is no way to get value from the hashcode. See hash-function definition. Hash values are not used to uniquely identify the original value, have values are not unique for each type of the input value.

A hash function may map two or more keys to the same hash value. In many applications, it is desirable to minimize the occurrence of such collisions, which means that the hash function must map the keys to the hash values as evenly as possible.

Answer 2

You cannot. Hashes are one way.

The thing with hashes is that you loose information. Independent of the length of the string, the result is always an integer. This means e.g. that getting the has of a string of 10,000 characters will also result in an integer. It is of course impossible to get the original string back from this integer.