I've been reading about how Tor and I2P use cryptographic addresses to send messages to other nodes, but how does this work? I looked through the documentation for each and neither is very clear on this. For two machines to communicate, you ultimately need the IP addresses at some level, right?

EDIT: Removing my second question as it is unrelated to my original. What I'm getting at is: if these anonymous networks are overlays built on top of the existing internet infrastructure, then they must be using TCP/IP protocols for nodes to communicate, right? So do these cryptographic addresses somehow translate to IP addresses? I'm not really looking for a Tor-specific or I2P-specific answer, just a general answer on how this works in overlay networks. I don't understand when the Tor/I2P documentation mentions that nodes communicate without knowledge of the others' IP addresses, only knowledge of their cryptographic address.

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  • Possible duplicate of Why can a Tor exit node decrypt data, but not the entry node? - also, this and this might help. – Polynomial Jul 1 '15 at 13:56
  • @Polynomial Edited my question to be more geared toward the original subject – Matt Jul 1 '15 at 14:22
  • Are you essentially asking how Tor hidden services (e.g. onion addresses) hide their IPs? Or are you asking about all individual nodes in the chain for communications? – Polynomial Jul 1 '15 at 15:35
  • Both. So for the individual nodes in the chain, they each know the IP address of the node immediately before and after it in the chain but no others? And the hidden service has introduction points, but the intro points would know the IP of the hidden service wouldn't they? Also, I guess I'm not understanding the connection between the cryptographic address and the IP address. – Matt Jul 1 '15 at 16:11
  • There isn't one, really. The idea is that the hidden service advertises the introduction node IDs, not its own IP, so they can introduce you to the hidden service without you knowing the IP of the target. There's a directory which holds the onion addresses and their associated introduction node IDs. – Polynomial Jul 1 '15 at 16:19

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