  Recently, several works conjectured the vulnerabilities of mainstream
blockchains under several network attacks. All these attacks translate into
showing that the assumptions of these blockchains can be violated in theory or
under simulation at best. Unfortunately, previous results typically omit both
the nature of the network under which the blockchain code runs and whether
blockchains are private, consortium or public. In this paper, we study the
public Ethereum blockchain as well as a consortium and private blockchains and
quantify the feasibility of man-in-the-middle and double spending attacks
against them. To this end, we list important properties of the Ethereum public
blockchain topology, we deploy VMs with constrained CPU quantum to mimic the
top-10 mining pools of Ethereum and we develop full-fledged attacks, that first
partition the network through BGP hijacking or ARP spoofing before issuing a
Balance Attack to steal coins. Our results demonstrate that attacking Ethereum
is remarkably devastating in a consortium or private context as the adversary
can multiply her digital assets by 200, 000x in 10 hours through BGP hijacking
whereas it would be almost impossible in a public context.
