The Two Generals’ Problem
Published -
- August 12, 2019
- 3:00 pm
Story Time!
Time to tell a story about idempotency, computer science, and the Night of the Multiple Orders.
What is the Two Generals’ Problem in computer science?
The Two Generals’ Problem: An Exploration of Communication and Coordination in Computer Science
In computer science, one of the classic problems that has puzzled experts for a long time is called the Two Generals’ Problem. This problem revolves around the issue of communication and coordination in a distributed system where there is a possibility of unreliable communication channels. The Two Generals’ Problem is relevant in computer networking, cryptography, and other areas of computer science where communication is an essential aspect.
The problem is simple and goes like this: Two generals, each commanding their own army, are planning to attack a city located between them. They need to coordinate their attacks to maximize their chances of success, but they are situated far from each other and can only communicate via messenger pigeons. Unfortunately, the pigeons are unreliable, and there is a chance that any message could be lost or delayed in transit. Thus, the critical question is, how can the two generals coordinate their attacks without the guarantee that the message will arrive safely?
The Two Generals’ Problem is a variation of the Byzantine Generals Problem, which is an abstraction of the distributed consensus problem. It was first introduced by Jim Gray and Leslie Lamport in their paper “Consensus on Transaction Commit,” published in 1982. The problem has since grown to become one of the most studied problems in computer science, and it has numerous applications today in blockchain, distributed systems, and other areas.
One of the solutions to the Two Generals’ Problem is by using a set of predetermined messages that the generals exchange in a specific order. The messages can be something like “attack” or “withdraw,” and they are sent back and forth until both generals agree on the same action. However, this approach has a few drawbacks. First, it is inefficient to send several messages back and forth, especially if there is a delay in the communication channel. Second, the method is vulnerable to attacks, such as a denial-of-service attack on the communication channels that result in a delayed message.
Another solution is by using digital signatures, where each general uses a distinctive signature to sign a message. A digital signature ensures that a message is authentic and has not been tampered with. The generals exchange their signed messages until both parties have the same set of messages. However, this method is also vulnerable to several cryptographic attacks and requires a pre-established trust between the generals to exchange their public keys.
In conclusion, the Two Generals’ Problem is a challenging problem in computer science that focuses on communication and coordination in a distributed system. Researchers have come up with several solutions to the problem, but none of them are perfect. The problem has numerous applications in various areas of computer science, and understanding its implications is essential for anyone working in the field. The Two Generals’ Problem is an excellent illustration of how, in computer science, a simple problem can have deep implications and challenges for researchers.
