4 ms·
Trying to understand this: 1. Alice sends message to Bob to attack on Tuesday and 9am 2. Bob sends message to Alice confirming this is fine 3. Alice sends co
by chris_wot 4y ago
Trying to understand this:
1. Alice sends message to Bob to attack on Tuesday and 9am
2. Bob sends message to Alice confirming this is fine
3. Alice sends confirmation of confirmation to Bob
4. Bob sends confirmation of confirmation confirmation to Alice
5. Alice sends confirmation of the confirmation of the confirmation confirmation to Bob
But at this point, Bob has realized there is a confirmation. Alice has realized there is a confirmation also. Surely this is sufficient?
- ebingdom 4y agoWhat if Bob never gets the confirmation from Alice in step 5? Or if Bob doesn't need it, why did Alice even send it?
- dahfizz 4y agoI was also confused by this. At a certain point, you are guaranteed that the other party got your original message.
- travisjungroth 4y agoYou can't have both parties be guaranteed the other party got the message at the same time.
- goto11 4y agoSure, but the point is that either army only attacks if they are 100% sure the other army also attacks. This is just not possible, since the last acknowledgement might have been intercepted by the enemy.
- hakuseki 4y agoI guess the idea is that Alice wants to be 100% certain that Bob will attack before she commits her own forces, and Bob similarly wants to be 100% certain that Alice will attack. This level of certainty is not achievable.
- hakuseki 4y agoFurther thoughts: Alice and Bob must each choose an actual policy for how many confirmations they need before they actually commit to attack. We can number the messages like this: 1. Alice's first message 2. Bob's first message 3. Alice's second message 4. Bob's second message ... Alice's policy can only commit to attack after receiving some even-indexed message n. Bob can only commit to attack after receiving some odd-indexed message m. So n and m cannot possibly be equal. Therefore the possibility exists that a message fails between n and m, and either Alice or Bob ends up attacking without the other's support.