Security between user and miner

How does the Ethereum / Bitcoin or at all a blockchain-network guarantee the security between a user (me) and the miner? Since I found a lot of information on how the security is reached and realized when a datablock is already put into the blockchain. But there is less information about the risk, that the transaction/information is messed up before reaching the blockchain.
Is there some encryption protocol that guarantees that the block that is put into the BC is the same as the one I sent?

I am pretty interested in the answer(s)!
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