Can you post the references for these papers?

sure. i got them from ftp.cwi.nl in directory /pub/CWIreports/AA/. CS-R9318.ps.Z is N. Ferguson "Single Term Off-Line Coins." it is 13 pp. CS-R9323.ps.Z is Stefan Brands "An Efficient Off-line Electronic Cash System Based On The Representation Problem." it is 77 pp. does anyone else have any digital cash papers on-line? peter