Within the United States (and most other sovereign states) Hal Finney is correct to point out that the power to print currency is reserved to the government. I would think that e-cash is a currency and therefore illegal TO ISSUE WITHIN the geographical (legal) domain of the US.

He didn't say it was illegal to print private banknotes, just taxable. Anybody can issue paper or metal tokens or whatever - the difference with goverment-issue currency is that they can pass laws saying you must accept it as payment for debts, even though your contract specified repayment in real money instead of private bogons like green paper IOUs or lightweight impure-metal coins with politician's pictures on them. As far as I know, the legal definition of a "dollar" in the US is still a certain weight of silver, and payment in silver legally satisfies debts; under current silver prices, that probably costs more than a $1 US Federal Reserve Note, so nobody bothers. Bill