As the function processes each chunk of plain text, it is generating hash valies. In order to decrypt the data and roll the operation back, you would need to know a vital piece of information about the function. This is the private key. Strictly speaking, a hash function takes variable length data, such as a text message, and performs one or more mathematical operations to convert the variable length data into a fixed length format. Hash functions are used not only in cryptography, but also in many other areas of computer science such as checksums and compiler technology.
Hash functions are handy things indeed.
The number 23 was selected because it is a prime number and would produce a relatively unique hash. The hash value for this string is simply the sum of the third column. In our example, the hash value is 70. Our simple hash function is not a very good hash function because it would produce many hash collisions . A hash collision is when two different strings produce the same hash value.