If malicious person(node) tampered withone block transaction, what's gonna happen?

Question

I understand that if one bad person(node) tampered one block of his/her blockchain, the block hash data changed completely different.

Let's say each node has 10 indexed blockchain and index4 block has transaction data like [Alice → Bob 10BTC]. Also the block has [00000000b78qgifg20b] hash as a valid data(stars with 8 zeros).

Now, one bad person(node) tampered index4 block's transaction data [Alice → Bob 30BTC] and the hash data changed from [00000000b78qgifg20b] to [f24yoxyn28hk8hohko].

Does this mean new block is created? If so, new block with [f24yoxyn28hk8hohko] is gonna be distributed to all nodes and added to their blockchain as a new mined block?

Answer 1

A few things would happen:

• The new block would be invalid because it doesnt start with 8 zeros
• Even if the bad person managed to mine the new block all the other nodes wont accept it because all the blocks after it would be invalidated and it would no longer be the longer chain, the chain would be 4 blocks long but all the other nodes would have a 10 blocks long chain.
• Even if the node managed to mine the block and also mine another 6 blocks on top of it the block would still be invalid because the transaction data (Alice → Bob 10BTC) was signed by Alice’s private key. After altering it to (Alice → Bob 30BTC) the signature is no longer valid because Alice didn’t sign it.

So what would actually happen is that all nodes that received the fake block would ban the bad node because it is sending them fake data and would never put it in their blockchain.