公钥

1. Uncompressed Public Key vs. Compressed Public Key
Since the inception of Bitcoin in 2009, the public key generated by the wallet is a 512-bit (64-byte) binary number. We will find that this public key connects the x and y coordinates together. However, once x is determined, the value of y will also be fixed, so as long as the value of x is collected, it also contains the information of y. This can significantly reduce the size of the data and lighten the storage burden (it will be mentioned later that every Bitcoin transaction must be encrypted using the public key, which will be stored on the blockchain), hence it is also referred to as 'compressed public key'. The earliest public key is called 'uncompressed public key'. To distinguish these two formats of public keys, the wallet adds a prefix '0x04' in front of the 'uncompressed public key', resulting in a 520-bit (65-byte) public key. Therefore, in 2012, after the Bitcoin wallet upgrade, support for compressed public keys began.