Learning about the Blockchain
Try this as a trivialised example in order to help people get their head around some of the ideas. It's not strictly accurate, but I think it will help with understanding the concept.


Start with a short message (in text) and round up to a multiple of 16 bytes, padding with spaces.
Replace the final space with a non-space character
Take the m5sum of the result, and look only at the last digit. If this is '1', you're done and have finished the block.
If you're not done, go back to step 2, and modify your non-space trailing padding.
After finishing a block, you can append a new message, pad again, and repeat the process of modifying the whole message to achieve the target hash.


In practice, the hash function is expensive to calculate (and will have far fewer collisions meaning many iterations will be required to search for a suitable padding section).

Although a single block could be modified, once the modified block has been wrapped into a subsequent block, a couple of times, the compute cost of re-writing an older message grows significantly.

What this generates is a publicly readable message, which can't be re-written in the future (and everyone can verify the accuracy or an old message).