1. Flamingo ensures that progress can be made in spite of honest clients that are offline, as long as enough clients are online. Flamingo also protects client privacy (i.e., only learns the sum from a large enough group of clients) from an adversary that controls the server and some number of clients. (Flamingo is robust to honest client dropouts up to some fraction of the total number of clients and a different fraction of the number of client decryptors, and Flamingo provides privacy against an adversary that can compromise up to some fraction of the total number of clients and a different fraction of the number of client decryptions.)

2. If a client drops out in round 1, its neighbors will help the server reconstruct the pairwise mask for that client. Then if the same client is online in round 2, it will provide the individual mask to the server. The server has both the pairwise mask and the individual mask, and so can see the client’s contribution. Flamingo fixes this problem by deriving new per-round seeds from a long-term seed using a PRF.