Digital payment systems were first explored in the 1990s. Some systems used the existing credit network, while some tried inventing a new cash system.
DigiCash was an early digital currency invented in 1989 that used a centralised server for validating transactions. It solved the anonymity problem by letting users pick the IDs in secret and have them signed by the server. This provided privacy for buyers, but not sellers.
HashCash (1997) involved senders solving hashes when sending emails to avoid spam emails.
Haber & Stornetta (1991) created a centralised ledger system for verifying timestamps on documents. Clients could send documents to the server to be signed with the current timestamp.
Q: When were digital payment systems first explored? A: 1990s, some using existing credit network, some with digital cash
Q: How did DigiCash (1989) work? A: Centralised server for validating transactions, buyers could pick an ID in secret and have it signed by the server, allowing for buyer but not seller privacy.
Q: What was HashCash (1997)? A: A system that made email senders solve a hashing problem to reduce spam. Made redundant by improved spam filters.
Q: What did Haber & Stornetta do in 1991? A: Created a centralised ledger system for verifying timestamps on documents. Clients could send documents to the server to be signed with the current timestamp.