Each block contains the root hash of all the transactions. Because of the one-way nature of hashing, anyone can look at this root hash and compare it to the data in the block and know whether all the data is valid and unchanged. This allows anyone to quickly verify that every transaction is correct. Each blockchain has small variations on this pattern (using different functions or storing the data slightly differently), but the basic concept is the same. Digital signatures
Now that we've covered hashing, it's time to go over a related concept:
digital signatures. Digital signatures use the properties of hashing to not only prove that data hasn't changed but to provide assurances of who created it. Digital signatures work off the concept of hashing but add a new concept as well: digital keys.