Say that many banks issue electronic cash of a particular type.
If there is a malicious bank and user collusion, the malicious bank signs electronic cash for a particular user. This user then takes the electronic cash to other banks to withdraw money. This way the malicious bank can get a large amount of cash from other banks.
Can such a multi-bank electronic cash system be established only if it all banks do not act maliciously?
Related multi-bank electronic cash papers: Fair Electronic Cash Systems with Multiple Banks