The explanation about PoSign isn't right in that article because he is saying that all nodes need to sign the block so it can be validated. If it work like that then anybody can sabotage XBY just by leaving one node offline. What really happens is that the nodes that are online at the time the transaction happen will sign the block and as i understood from Jhar the nodes that were offline will doublecheck the block when they come online but don't need to sign the block themselves.
This is correct, all ONLINE nodes sign the block. There is some more info on this here:
"Many questions have been asked about XTRABYTES' core technology, features, and advantages. The following summary seeks to address those questions and to further elucidate various aspects of the XTRABYTES platform.
Security is at the heart of XTRABYTES' technology and is where its principal advantage lies. XTRABYTES leverages the concept of digital signatures extensively in its security algorithms. Common examples of digital signatures include SSL and Microsoft's signed software, but XTRABYTES goes several steps further to ensure the robustness of its signature protocol.
Simply put, as the number of digital signatures increases, level of security increases. XTRABYTES employs this tenet in its core technology—STATIC nodes rely on multiple layers of encrypted and digitally signed sources to guarantee the integrity of the network, while competitor systems rely either on a single signature only, or even none at all.
It is impossible to steal all signatures, given that not all STATIC nodes are online at a given time, and that they use different operating systems (eg. Windows. Mac. Linux)—and even if a virus compromises all online STATIC nodes, a single off line STATIC node is capable of restoring the network once reactivated.
Further, online keys are intermediate only—deposit and genesis keys are private and always offline—and consequently can easily be changed if necessary. If such a signature is compromised, the associated STATIC signature will automatically be revoked as the consensus among nodes has been violated. The owner of the affected STATIC node is then warned to generate a new signature before the node can resume participation on the network.
STATIC nodes communicate with one another via the PULSE system. If nodes are online, the system behaves like instant messaging, while offline nodes are always automatically forwarded missed messages by the network. All of these transmissions are encrypted, secured.and time-stamped. This is in direct contrast to the Bitcoin network whose peers communicate with one another in an unsecured fashion.
Level 2 nodes will be similar to the original STATIC nodes save for the fact that the intermediate signatures will be declared in a future block, not in the genesis block. All STATIC nodes will have a TRUST index number. "
The author is on Slack, might want to get in contact.
