Hash value is based on a key in public-key encryption. This value is written on the computer from a 'base input number' using a complex hashing algorithm. Basically, the hash value is just a summary of the starting value. The most important thing about a hash value is that it is nearly impossible to get the original input number without knowing the data used to create the hash value.
Here's a simple example:
|Input number||Hashing Algorithm||Hash value|
|10,663||Input # x 142.5||1,525,379|
You can probably see how hard it is to decipher that the value 1,525,381 came from the multiplication of 10,663 and 142.5. But if you knew that the multiplier was 142.5, then it would be simple to calculate the input value 10,663. Public-key encryption is actually much more complex than this example, but that's the basic idea behind it.
Public keys mostly use complex algorithms and very big hash values for encrypting. This includes '50-bit' or even '130-bit numbers'.
A 130-bit number has a possible #2128, or 3,402,823,669,209,384,634,633,746,074,3 x(10x38) different combinations.
This would be like trying to find one particular grain of sand if all the beaches in the world where combined together.