I stumbled upon the following text in the article about onion routing on Wikipedia:
In this example onion, the source of the data sends the onion to Router A, which removes a layer of encryption to learn only where to send it next and where it came from (though it does not know if the sender is the origin or just another node). Router A sends it to Router B, which decrypts another layer to learn its next destination. Router B sends it to Router C, which removes the final layer of encryption and transmits the original message to its destination.
Now I am wondering how the entry node can not know that it's talking to the originator. Couldn't it simply check the list of all tor nodes and see that the IP is not a tor node? Or did I misunderstand the concept of tor clients... I thought clients are not automatically nodes.
And are the data packages that are being sent between the node always of the same size? I guess otherwise I would be pretty easy to check what is going on.
Please help me and sorry for my English, I'm not a native speaker.