eCash

The blind-signature proposal appears in Blind Signatures for Untraceable Payments at CRYPTO ’82; the proceedings were published in 1983. DigiCash later applied related technology in eCash. Its 1994 network demonstration and CyberBucks trial belong to the product's history, not to a product launch in 1982.

Payment records can expose a person's movements, relationships and habits. Chaum sought electronic payments that resist forgery without giving the institutions handling them a complete record of the payer's spending. The aim was to bring some of physical cash's privacy properties into electronic payments.

The user masks data representing electronic cash with a random value and asks the bank to sign it. Removing the mask leaves a valid bank signature, while preventing the bank from matching the resulting cash to its withdrawal. The merchant submits the cash to the bank, which checks whether it has already been spent.

This is the online blind-signature payment model: the bank still issues, validates and redeems the cash, so its continued operation matters. Blind signatures reduce the link between withdrawal and payment; they do not turn issuance or double-spending checks into a public network independent of a bank.

On February 12, 2009, Satoshi explicitly compared Bitcoin with Chaumian cash: both use digital signatures, but their privacy and double-spending mechanisms differ, and Bitcoin has no central server. This documents his awareness and discussion of that approach; it does not establish that Bitcoin adopted eCash's blind-signature mechanism.

A researcher in cryptography and payment privacy, Chaum earned a computer science PhD at UC Berkeley and founded DigiCash. His research also includes anonymous communication and electronic voting.