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Block: It is a data block, just like a file. The current design is that the Bitcoin transaction records that occur in the network every 10 minutes are packed into a data packet, which is a data block, called a block.

Why is the ledger managed according to data blocks? We can imagine that for past transactions, if it is determined that it has occurred correctly, then these data will never be changed, and the ledgers stored in all nodes should be consistent. Then we don't need to verify whether the past transaction records are correct every time, but just back up and lock these accounts. How to lock it, the concept of "fingerprint algorithm" is introduced here:

    Perform a hash algorithm such as MD5 or SHA1 on a data packet to obtain a 128-bit or 256-bit data. This data is the characteristic of the data packet, just like our ID card, which is unique. If someone changes the data packet, even if it is 1 bit, the hash code obtained after re-executing the MD5 or SHA1 algorithm will be different. So we only need to recalculate it once to know whether the data packet has been changed. Now online publishing programs usually use this method to ensure that the published programs have not been changed by hackers. If someone modifies a data packet and changes the MD5 or SHA1 code, how do you determine whether the data packet has been changed? Here is the introduction of "asymmetric encryption algorithm", now the most commonly used is usually based on RSA encryption method, RSA is divided into a private key and a public key, the private key is owned by the author who publishes the data packet, and is not disclosed to the outside world and is absolutely confidential. The public key is public and anyone can obtain it. When the author publishes a data package, first encrypt the data package with the RSA private key, and then when we get the data package, we can use the public key to decrypt and restore the data package. Note here that after the private key is encrypted, only the corresponding public key can be decrypted. If it is not the data package released by the author, and the alive data package is changed, the data obtained after decryption with this public key must be incorrect. This ensures that the data package is from the author's original data package, and must not have been altered by hackers during the period.