Hi @mariog,
Fast flashing cyan on your core indicates that the secure handshake is failing on your core. This can also be represented by flashing orange: Particle Welcome to the Particle docs .
Can you try these steps and email us your new core public key / id at hello@spark.io ?
edit: I would say that the 'malformed packet' stuff is probably a red herring at this point, we're sending coap, but the handshake itself isn't coap, and the messages after the handshake are encrypted.
Thanks!
David