E-cash (Cashu, Fedimint)
Also · Chaumian e-cash · Mint · Blind signatures
E-cash is bearer digital money issued by a mint that holds bitcoin and signs tokens blindly, so it cannot link a withdrawal to a spend. Cashu uses 1 mint, Fedimint a federation.
David Chaum described e-cash in 1982. A user sends bitcoin, usually over Lightning, to a mint, which returns tokens signed with a blind signature. The mint certified the tokens without seeing them, so when they come back to be spent or redeemed it cannot tell who withdrew them. Tokens are files. They change hands instantly, offline if needed, and leave no trace on Bitcoin or Lightning.
The mint holds the bitcoin, so this is custody with privacy, not self-custody. Cashu keeps it simple with a single operator per mint, suited to small balances. Fedimint spreads the custody across a federation of guardians, so that no single member can run off with the funds. Both pay out to Lightning when a user leaves.
In French · E-cash (Cashu, Fedimint)
