Mining involves securing transactions by collecting multiple transactions together along with some additional information and calculating a SHA256 hash. If the value of the hash is less than a specified target, then the block is complete. If the value of the hash is not less than a specified target, then the miner increments a number in the header of the block and tries again. This process is repeated until somebody finds a hash that has a low enough value.
This makes it difficult for anyone to modify the contents of the block, because that would change the hash and it would no longer be considered valid by the network. Since each new block contains the hash of the previous block, it would require someone with more computing power than every other miner combined to catch up with the new blocks being created in order to remove or replace transactions in the past.
Since the hash is a mathematical formula that is very fast/easy to generate from the data, but it is impossible to determine the data from the hash, I'm not sure what part of this process you are concerned about.
No, there is no "cracking the transaction" occurring.