The key of bitcoin can be divided into private key and public key.

The private key is a 256-bit random number, which is generated by the Bitcoin wallet and can only be known by the owner of the wallet. The private key is the core of bitcoin transactions, because only the holder of the private key can sign, thus authorizing the transfer of bitcoin.

The public key is generated from the private key by mathematical algorithm. Specifically, the public key is generated by decrypting the private key encrypted by the elliptic curve. The public key is usually used to receive bitcoin, because people can share it publicly without revealing the private key.

Bitcoin address is generated by public key through hash algorithm. A bitcoin address is a long string of numbers and letters that can be used to receive bitcoin. Anyone can see the bitcoin address, but only the person who holds the private key can authorize the transfer of bitcoin.

Therefore, the private key is the cornerstone of bitcoin security, because only the private key holder can control bitcoin. Unless the private key holder authorizes or discloses the private key, no one else can access or manipulate the holder's bitcoin.