Offline transfers don’t work without risk of double spending. The transactions eventually have to be finalized with a mint. The most one could hope for in the DigiCash model is the detection of a double spend once the cheated parties go back online[1].
If only the recipient doesn’t have access, a certain amount of trust can be delegated to the strength of the proof presented in the spend. In an ecash model, the proof would be in the form of a signature made by the mint (assuming the recipient was able to get the public keys the mint was using).
Active research is being done on the ecash model with the resurgence of the concept in the Cashu and Fedimint projects. Cashu takes the online sender, offline receiver approach[2].
If only the recipient doesn’t have access, a certain amount of trust can be delegated to the strength of the proof presented in the spend. In an ecash model, the proof would be in the form of a signature made by the mint (assuming the recipient was able to get the public keys the mint was using).
Active research is being done on the ecash model with the resurgence of the concept in the Cashu and Fedimint projects. Cashu takes the online sender, offline receiver approach[2].
[1] https://chaum.com/wp-content/uploads/2021/12/Untraceable_Ele...
^See paragraph in the introduction ending with:
“But if Alice reuses a coin, the bank can trace it to her account and can prove that she has used it twice.”
[2] https://x.com/CashuBTC/status/1901240537866273252