A peer-to-peer network is a user layer where people communicate directly with each other and exchange information. When you talk to your friend directly, you create a peer-to-peer connection. But if you make a phone call to him, your call is checked by a server and then notified to your friend. This connection is no longer peer-to-peer.
In principle, peer-to-peer communication does not exist in centralized systems and is specific to decentralized networks. In a centralized system, all the information is usually located on the server. So, to access them, you have to send a request to the server and receive it if approved by the server. In this case, if you download all the data from the server and store it in your system, you can access the information without the need for a server.
In a blockchain network, people do exactly that and all the data on the network is stored on their computers. So if a user leaves the network, other users still have access to the data and can exchange information with each other. When a new block is formed, its data is broadcast on the network and people can update their ledger.
How is ownership ensured in the blockchain space?
Concepts such as username and password, which are common in conventional systems, are not applicable in the blockchain network. To prove ownership in this space, public key cryptography or asymmetric cryptography is used. This type of cryptography uses two public and private keys. This feature makes this method highly secure and has made it widely used in computer systems and blockchain networks.
In order to be able to receive cryptocurrency from others, users must create their own private key. The private key is a very long random number that it is impossible for anyone to guess even if it takes hundreds of years. Of course, if someone else gets the private key, they can claim ownership and spend the funds by entering the password. Therefore, everyone must keep their private key secret.
In the previous paragraph, it was said that the private key should not be given to anyone else. Now the question that arises is how the other party transfers currency to us. The answer to this question lies in the public key. The public key can be given to others. In fact, the public key is considered to be your account number in a way. It is almost impossible to convert the public key to a private key, so this method provides very high security for users.
How is security ensured in blockchain?

Blockchains ensure their security by means of several mechanisms that include advanced cryptographic techniques and behavioral models of mathematical decision-making. In many blockchain applications, the issue of immutability and security is very crucial. This section discusses how to provide these two important features.

Consensus and Immutability
Consensus refers to the ability of nodes in a network to reach a consensus to record transactions and create blocks. In contrast, immutability refers to the ability to prevent transactions that have already been recorded in the system from being copied. Together, these two features provide security for the blockchain.
Consensus algorithms ensure that the rules of the network are being followed and that all network members agree on the current state of the network. While immutability ensures the integrity of data and the record of transactions made after each block is validated.