IOTA can theoretically have a hard fork. In order for that to happen, a few things must occur:
1) The forker must decide on a state of the tangle that will be used for the fork. This is more difficult than in blockchain because there aren't specific blocks, the tangle is constantly changing.
1a) This depends on the definition of fork -- in blockchain, ...
Most of IOTA is open source, and the parts that are not (like the Coordinator) can be implemented by interesting parties themselves (no guarantee that their Coordinator is on par with IOTA's, though).
Therefore, it can be forked, and it has already happened.
The fork was without forking the ledger (like Litecoin is a fork of Bitcoin), so IOTA holders did ...
Due to the dag structure of the Tangle a complete ordering of transactions is impossible. Therefore, the protocol don't relies on transaction time ordering to determine which of two conflicting transactions is the legitimate one. By design, the protocol will decide that the transaction with most weight will be the accepted one.(here is a brief explanation of ...
The paper referenced in the question try to demonstrate that the tangle cannot resist to a 51% attack. Nothing really new here.
The position of the Iota Foundation is to favorise a stable organic growth of honest transactions (as founders said multiple times on discord, reddit, ...)
Some members of the community suggested to include a spammer on IRI nodes ...
Here is what a blockchain looks like. The major restriction compared with a pure DAG is that a vertex (here called block) cannot have more than one parent. So, yes a blockchain is a dag with the restriction that a vertex cannot have more than one parent.
My paper states that any tip selection that uses the weight of sites to select tips are subject to double-spending attack if the amount of hashing power used by nodes to generates honest sites is smaller than the hashing power of an adversary. This is not very surprising as ben75 said this is just the non-resistance to 51% attack.
About the implication "all ...
All that we know is that Tf and Tg come after Ta,Tb, Tc
...and the transactions (directly or indirectly) referenced by Ta, Tb, Tc.
That is all the Tangle "knows" about the temporal order of these transactions. It makes no statement about the temporal order of the independent (neither directly or indirectly referencing each other) transactions Tf and Tg.
A DAG is just a mathematical concept were you have directed edges and vertices, with the property that if you start from a vertice a follow the edges (in the correct direction): you cannot visit a vertice more than once.
When it comes to computer science: a DAG is a particular data-structure (understand "data-structure" as "a way to organize information") ...
r/(r+λh) is a mean value ( < 1 )
r is tips before time [t-h]
r+λh is a slightly higher number adding all tips from time interval [t-h,t]
since the node does not know λh tips are no tips any more at time index t (assuming λh is always stationary value), we have a total probability of choosing a tip of r/(r+λh) ( < 1 )
Total mean number of chosen tips ...
Ales has his own take, but I think he is perhaps ruling out smart contracts based on perceived functionality from other implementations.
Even if all transactions have timestamps on them, we cannot be sure that all these
timestamps are accurate (there can be some malicious nodes that want to fool the
network about the ...
In IOTA timestamp accuracy cannot be trusted.
"The tangle is a graph with only a partial order structure, which
makes it difficult (in fact, generally impossible) to establish the
correct time order of transactions. Even if all transactions have
timestamps on them, we cannot be sure that all these timestamps are
Expected increment of # of tips at time t is:
1 - 2*r/(r+λh) .....eqn(1)
where "1" refers to new tip created by the tx and "2*r/(r+λh)" refers to expected # of "erased" tips.
If the two "erased" tips were already approved (usually for small L(t)), then "2*r/(r+λh)" = 0, thus eqn(1) becomes positive or increasing.
If the two "erased" tips were not ...