The only thing a user needs to log in to Vibrant is their phone number. That's it. No secret key, no password, just a phone number. That's because a SEP-30 wallet like Vibrant doesn't manage and backup a single master key. Instead, it manages device keys, and uses multi-sig and distributed servers to create new ones when necessary. It still does many of the same things other wallets do — it stores and protects a key; it helps a user sign transactions; it prevents loss — but the loss it prevents is different: it prevents users from losing their accounts, not their keys.