Quote from: Prattler on March 10, 2013, 08:03:10 PM

Assumptions:
1. Bitcoin is fully adopted tomorrow, the network is 100,000 full nodes.

Why so many? I'm not sure why the Bitcoin P2P network would need so many nodes to be secure. A good geographical distribution may be desirable to avoid latency and government censorship but can be achieved with far less nodes.

Quote from: Prattler on March 10, 2013, 08:03:10 PM

The network is also crunching 1000+ transactions/second, requiring UTXO (unspent tx outputs) lookup to be fast.
2. UTXO need to be stored in fast access storage. https://en.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposures#CVE-2013-2293 . You could maybe make a system setup of multiple HDD systems, but that wouldn't be cheap, at least not as cheap as "HDD space is cheap". Not if you're using 100 disks to do fast seeks.

Agreed but you can use several tricks to avoid looking up the storage to protect against this kind of attack. For example Bloom Filters or preferably counting Bloom Filters (to make them more resilient as UXTOs can be volatile) can be used to avoid hitting the disk by detecting invalid outputs early. This is a bit costly to setup (generating the filters is I/O intensive and they must be regenerated when they aren't big enough to handle the growth of the UTXO database and their efficiency plumets).
Developers are smart and know about them

(see BIP 0037).

Quote from: Prattler on March 10, 2013, 08:03:10 PM

3. 1 unspent dust output takes 100 bytes of memory.
   Prattler: should be 41.5 bytes for each transactions which is not entirely spent (excluding any of its outputs)
   plus 23 bytes for each unspent output
   in-memory it's a lot more, but that's just the lowest-level cache
4. RAM costs $0.008/MB, SSD costs $0.001/MB.

A bloomfilter is quite efficient and can use a few bits per entries (unspent TX) it needs to filter (10 bits give you a ~99.9% efficient filter). The RAM cost in this case is negligible vs the SSD cost. You can store a billion unspent TX on a system with a couple of GB today and have to hit the disk during an attack one time out of one thousand transactions.

Quote from: Prattler on March 10, 2013, 08:03:10 PM

For example http://blockchain.info/tx/0fda0a78210e2913ba269b3a5ff9385d29a004873333f44e56eb9efb1a488f72
Assuming the dust output is never spent and the network has to store it on:
1) RAM the network UTXO storage hardware cost is $0.08.
2) SSD the network UTXO storage hardware cost is $0.01.

Ok. $0.08 might not sound like much, but remember the fees go to the miner, the network full nodes get nothing!

I believe you can ignore the RAM cost with a software update.
But why would you run a full node if you aren't a miner? The only reason I can see is because a SPV client security wouldn't be enough for you. Why would it be and why would it be for hundred of thousands of people?

We may see the situation from the opposite angle: if the costs of storing UTXO rise and there's only a market for one thousand full node instead of 100 000 (being paid by miners using them), then some people will run at a loss and/or full nodes will shut down until there is only 1000 of them.

And it boils down to: what is the minimum size of the Bitcoin P2P network considered healthy/secure when it's mainly composed of nodes being paid by miners.