1. Nakamoto, S.: Bitcoin: A peer-to-peer electronic cash system. Technical Report, May 2009.
http://www.bitcoin.org/bitcoin.pdf
2. Back, A.: Hashcash - a denial of service counter-measure. Technical Report, August 2002. (implementation released in Mar 1997)
3. Lolcust: [announce] tenebrix, a cpu-friendly, gpu-hostile cryptocurrency, September 2011.
https://bitcointalk.org/index.php?topic=45667.0
4. Coblee: [ann] litecoin - a lite version of bitcoin. launched! October 2011.
https://bitcointalk.org/index.php?topic=47417.0
5. King, S.: Primecoin: Cryptocurrency with prime number proof-of-work. Technical Report, July 2013.
http://primecoin.org/static/primecoin-paper.pdf