A money warehouse receipt.
You send your bitcoin to someone else, who in return gives you a blind signature.
Now you can give this signature to others, and they can give it back to the mint to get the real sats back.
Think of it as a paper iou that can be redeemed for pure gold.
Awesome! Assuming that makes all the transfers of the ecash completely private?
Yes, it has "theoretically perfect anonymity", meaning that each transfer could have been done by any user of the mint, the anonymity set is the size of all users.
Furthermore it's basically instant and free.
Unfortunately the person running the money warehouse can run away with your real bitcoin...
That's cool. And no way to have like a custodian that can't run away with the sats? Like the only way to get access to the actual sats is with the blind signature that only the depositor has?
I like the way you’re thinking…
