Security concerns

[lsaether]

As I'm working on building up this repo using the bytes encoding I will use this GH issue to document possible security concerns that occur to me.

1. Pre-image attack. Since we now use the hash of the encoded transaction bytes, it is possible for many ScheduledTransactions to be deployed pointing to the same data represented by IPFS hash. We may then get an attacker who attempts to break the system by scheduling the same transaction n times. We must build timenodes which are resilient to this kind of attack.

[adibas03]

as for the issue raised, a possible solution would be to add points of check (in other words, other variables ) which could be confirmed by nodes to ensure that the right transaction is being executed