Zerocoin is trying to solve the second problem.
Combining 5 proof of work standards just gives you 1 new one. (There might be some robustness to be gained, though.)
Combining 5 proof of work standards just gives you 1 new one. (There might be some robustness to be gained, though.)
* disconnected operation (solve the double spend problem in a disconnected setting) (this would really make something gold-equivalent)
* a provably correct, but cryptographically secure ledger (meaning real anonymity)
* proof of work based on a single crypto standard seems risky. Use 5 of them.
* provably no way to compromise the network even with overwhelming computational power