Hashing explained in an EASY to understand way?

The basic idea of a hash is simple. It's a function applied to some sort of data structure that takes the contents of the data structure and computes a number.

The "hash" comes from the food sense of the word...mixed up leftovers made into a a meal. A hash function "mixes up the bits" in some fashion to arrive at a single number that has no apparent relation to the original input bits.

Cryptographic hashes tend to be very large numbers (hundreds of bits) with a vanishingly low probability of random collisions (two different inputs producing the same hash result) and a requirement that there be no way to determine any input bits from just looking at the hash result (even if "metadata" about the input like the input length were known), and that it be computationally impractical to generate an input that produces a particular hash result.

Hash codes used in associative arrays aren't so picky. They want a more or less even distribution of output codes over the anticipated set of possible inputs, plus a low probability of collisions.

Hashing is similar to a mapping function. You map some values to some other so that you secure them, or reduce their size, search easily and many more. There are a lot of hashing algorithms depending on the usage. You can search for simple hash algorithms and try to understand them. Hope this link helps you a little:

http://faculty.cs.niu.edu/~freedman/340/340notes/3...

Let me give you an example of simple hash function that generates a 32-bit code.

Set the 32 RESULT bits to zero.

- START -

Read one byte of the file into HOLD.  If the end-of-file has been reached, we're done — display RESULT and exit.

Left-shift RESULT by one.  If a carry out of bit-31 occurred, flip bit-0.

XOR the low byte of RESULT with HOLD.

Go to START.

Hash tagging?