// QueryMembership queries for an event with a key in a particular snapshot in the balloon.
// Returns an answer (is member?), an event (if the answer is true), and a proof (always).
// Run by the server with untrusted input (key and queried).
func (balloon *Balloon) QueryMembership(key []byte, queried *Snapshot,
vk []byte) (answer bool, event *Event, proof QueryProof, err error) {
answer = false
// verify the queried snapshot
if !util.Verify(vk,
append(append([]byte("snapshot"), queried.Roots.History...),
append(queried.Roots.Treap, queried.Previous...)...),
queried.Signature) {
return answer, nil, proof, errors.New("invalid signature")
}
// verify the length of the key
if len(key) != util.HashOutputLen {
return answer, nil, proof, errors.New("invalid key length")
}
// check hash treap for hash of key
proof.TreapProof = balloon.treap.MembershipQuery(util.Hash(key))
// if not in treap, then a non-membership is done
if proof.TreapProof.Value == nil {
return
}
// the position (index) of the event in the history tree
index := util.Btoi(proof.TreapProof.Value)
// was the event added _after_ the queried for snapshot was created?
if index > queried.Roots.Version {
return
}
// ok, now we know it's a membership proof, so we query the history tree
proof.HistoryProof, err = balloon.history.MembershipProof(index, queried.Roots.Version)
if err != nil {
panic(err)
}
// get the event from storage
e, err := balloon.Storage.LookupEvent(key)
if err != nil {
return
}
return true, e, proof, nil
}
// Verify verifies a proof and answer from QueryMembership. Returns true if the
// answer and proof are correct and consistent, otherwise false.
// Run by a client on input that should be verified.
func (proof *QueryProof) Verify(key []byte, queried, current *Snapshot,
answer bool, event *Event, vk []byte) (valid bool) {
// verify the snapshots
if !util.Verify(vk,
append(append([]byte("snapshot"), queried.Roots.History...),
append(queried.Roots.Treap, queried.Previous...)...),
queried.Signature) {
return false
}
if !util.Verify(vk,
append(append([]byte("snapshot"), current.Roots.History...),
append(current.Roots.Treap, current.Previous...)...),
current.Signature) {
return false
}
// check the authenticated path in the hash treap
if !proof.TreapProof.Verify(util.Hash(key), current.Roots.Treap) {
return false
}
// a non-membership proof where there is no event in the treap
if !answer && proof.TreapProof.Value == nil && event == nil {
return true
}
// a non-membership proof where the event was added _after_ the queried for snapshot
index := util.Btoi(proof.TreapProof.Value)
if !answer && index > queried.Roots.Version {
return true
}
// a membership proof
if answer && event != nil && util.Equal(event.Key, key) && proof.HistoryProof.Verify() &&
proof.HistoryProof.Index == index && proof.HistoryProof.Version == queried.Roots.Version &&
util.Equal(proof.HistoryProof.Root, queried.Roots.History) &&
util.Equal(proof.HistoryProof.Event, util.Hash(event.Key, event.Value)) {
return true
}
// otherwise the proof is invalid
return false
}
