1. FISCO BCOS uses accounts to identify and distinguish each independent user. In a blockchain system that uses a public-private key system, each account corresponds to a pair of public and private keys. Among them, the address string obtained by calculating the public key through a secure one-way algorithm such as hashing is used as the account name of the account, that is, the account address. The private key known only to the user corresponds to the password in the traditional authentication model. Such accounts with private keys are also often called external accounts or accounts.

2. The smart contract deployed on the chain in FISCO BCOS also corresponds to an account in the underlying storage. We call this type of account a contract account. The difference between it and an external account is that the address of the contract account is when it is deployed. Determined, calculated based on the deployer's account address and the information in his account, and the contract account does not have a private key.

3. The SDK needs to hold the external account private key and use the external account private key to sign the transaction. In the blockchain system, every call to the contract writing interface is a transaction, and each transaction needs to be signed with the account's private key.

4. Permission control requires the address of an external account. The FISCO BCOS permission control model determines whether there is permission to write data based on the external account address of the transaction sender.

5. The contract account address uniquely identifies the contract on the blockchain. After each contract is deployed, the underlying node will generate a contract address for it. When calling the contract interface, the contract address needs to be provided.