Plasma World Map - the hitchhiker’s guide to the plasma

[ldct]

This is trivial to spam attack with a modest budget:

1. Create a few coins.
2. Send them around to other addresses that you own creating a long history
3. Exit intermediate states simultaneously and fill the gas limit. ie, say 80 exits / eth block assuming 100K gas per exit.
4. Keep exiting for the next 10,000 blocks. Some challenges will block exits but many wont.

Why would the plasma contract allow the same coin / range of coins to be successfully withdraw multiple times? The whole point of the plasma cash design is to segregate deposits in such a way that this cannot happen.

in which case challengers can run out of money fast tied up in challenges

If the plasma chain is functioning correctly (only valid and available blocks are committed), there is no need to make challenges that do not immediately succeed (proof: the only invalid exits possible are exits of spent coins, and those can be challenged and cancelled by showing the spend of the coin). Hence

1. assuming the child chain mechanism does not get compromised, there are no serious attacks possible against users (the “tie money up in challenges” attack is not possible) in plasma cash; this is no worse than in gluon
2. assuming the child chain mechanism does get compromised, a “tie up money in challenges” attack is possible, but this is no worse than in gluon, wherein users will lose money

If the child chain is compromised, the chain should halt immediately in a POA model

When I say the “child chain mechanism” I mean all things not enforced by the plasma contract, including the blocks committed and the outcome of the token vote. Hence the hypothesis of this case analysis is that the PoS block producers maliciously commit invalid/unavailable blocks and also that the token vote to stop them does not happen or does not pass the 10% threshold.

[bharathrao]

The whole point of the plasma cash design

The general point I made was about an inherent weakness of all reactive security models: If the security of the system depends on someone monitoring exits and having to react within a few blocks, then it can be spam attacked. The details would be different for each flavor. In Plasma Cash for example, they may create, transfer and exit huge amount of spent coins simultaneously. The key point is that if challenges are they key to security, a spam/congestion attack is possible and the security cannot be assumed to be equivalent to root chain.