Hello,
Why is the Tor designed so that it need a middle node?
Thank you
The 3-hop path offers good anonymity. None of the 3 nodes knows your input and output IP.
More info: tor.stackexchange.com why-does-tor-use-three-hops-instead-of-two
Quote @arma: “3 is a good number for anonymity”
The best Tor path length would be an interesting research project.
The standard 3 hop path in pictures on my exit page
How Tor works
How do onion services work
Building a two-hop circuit is possible as well as
HiddenServiceSingleHopMode see man torrc | grep HiddenService
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Hello,
Thanks again.
So, the more nodes are better?
Like Bitcoin, the more number of confirmations in sending and receiving is better.
Not necessarily. A big adversary like the NSA can monitor almost all internet traffic worldwide. It doesn’t matter if you have 3 or 10 hops. 
Each Tor router must decrypt one layer. The more hops, the slower Tor becomes. The network latency is getting awful.
On_the_Optimal_Path_Length_for_Tor
Selected Papers in Anonymity
With hidden services it can make sense to configure HSLayer2Nodes and HSLayer3Nodes together with the vanguards add on. See Mike Perry’s README_TECHNICAL & README_SECURITY and announcing-vanguards-add-onion-services.
Usually it is 6 confirmations to complete your transaction, but they are p2p and not several nodes in a row.
Quote Pranshu Agarwal:
“This solves the problem of double spending. The 6 confirmations are required to stop someone attempting double spend. There’s nothing magical about 6, it’s just a number that was suggested early on.
The 6 confirmations means, there are 5 further blocks attached in the bitcoin blockchain after your block (the block, where your transaction is stored) which confirms your transaction was legit.”
The Bitcoin network is secured by mining, 100s of thousands or millions of ASIC miners doing a POW puzzle and convert electrical energy into heat. 
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Hello,
Thanks again.
Are HSLayer2Nodes and HSLayer3Nodes useful when launching the bridge?
A bridge + PT has the same function as a guard, the first hop in the circuit. You can only use bridge fingerprints in EntryNodes.
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Hello,
Thanks again.
What is a PT?
PT= pluggable transports
Tools that Tor can use to disguise the traffic it sends out. This can be useful in situations where an Internet Service Provider (ISP) or other authority is actively blocking connections to the Tor network.
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