If you want to understand Bitcoin right down to the data structure, network packets and encyption algorithms, check out these articles, including Bitcoin mining with pencil and paper. (I'm hesitant to tout my own articles, but I think they are what you're looking for.)

http://www.righto.com/2014/02/bitcoins-hard-way-using-raw-bi... http://www.righto.com/2014/09/mining-bitcoin-with-pencil-and... http://www.righto.com/2014/02/bitcoin-mining-hard-way-algori...