There have been a few such systems. One of the earliest was David Chaum's Ecash [1]. The first three references on that page link to papers covering technical d

There have been a few such systems. One of the earliest was David Chaum's Ecash [1]. The first three references on that page link to papers covering technical details. Here's a paper analyzing several digital cash protocols [2]. [1] https://en.wikipedia.org/wiki/Ecash https://en.wikipedia.org/wiki/Ecash [2] https://ethz.ch/content/dam/ethz/special-interest/infk/inst-infsec/inst-of-info-security-dam/documents/secrypt2015.pdf https://ethz.ch/content/dam/ethz/special-interest/infk/inst-...