After looking into it more, I think the implementation is more Coelho et al than hashcash. Sorry, this was long ago for me.<p><a href="http:&#x2F;&#x2F;www.cri.ensmp.fr&#x2F;classement&#x2F;doc&#x2F;A-370-v2.pdf" rel="nofollow">http:&#x2F;&#x2F;www.cri.ensmp.fr&#x2F;classement&#x2F;doc&#x2F;A-370-v2.pdf</a>