From Traditional Fault Tolerance to Blockchain. Wenbing Zhao. Читать онлайн. Newlib. NEWLIB.NET

Автор: Wenbing Zhao
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Зарубежная компьютерная литература
Год издания: 0
isbn: 9781119682110
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illustrated in Figure 1.2. When a system fails, it takes some time to detect the failure. Subsequently, the system is restarted and the most recent checkpoint in the log is used to recover the system back to that checkpoint. If there are logged requests, these requests are reexecuted by the system, after which the recovery is completed. The system then resumes handling new requests.

Schematic illustration of the rollback recovery is enabled by periodically taking checkpoints and usually logging of the requests received. Schematic illustration of redundant instances in the system, the failure of a replica in some cases can be masked and the system continue providing services to its clients without any disruption.

       ◾ Operation. A system is dynamic in that it is continuously processing messages and changing its state. The code as well as the execution environment must be protected from malicious attacks, such as the buffer-overflow attacks.

       ◾ System state. The system state refers to that in the memory, and it should not be corrupted due to failures or attacks.

       ◾ Persistent state. System state could be lost if the process crashes and if the process is terminated. Many applications would use files or database systems to store critical system state into stable storage.

       ◾ Message. In a distributed system, different processes communicate with each other via messages. During transit, especial when over the public Internet, the message might be corrupted. An adversary might also inject fake messages to the system. A corrupted message or an injected message must be rejected.

Schematic illustration of main types of assets in a distributed system.

      When we say a system is secure, we are expecting that the system exhibits three attributes regarding how its assets are protected [2]: (1) confidentiality, (2) integrity, and (3) availability. Confidentiality refers to the assurance that the system never reveals sensitive information (system state or persistent state) to unauthorized users. The integrity means that the assets are intact, and any unauthorized modification to the assets, be it the code, virtual memory, state, or message, can be detected. Furthermore, messages must be authenticated prior to being accepted, which would prevent fake messages from being injected by adversaries. The interpretation of availability in the security context is quite different from that in the dependable computing context. Availability here means that the asset is accessible to authorized users. For example, if someone encrypted some data, but lost the security key for decryption, the system is not secure because the data would no longer be available for anyone to access. When combining with dependable computing and in the system context, availability is morphing into that defined by the dependable computing community, that is, the system might be up and running, and running correctly so that an authorized user could access any asset at any time.