in pir.cpp [251:259]
string serialize_query(vector<vector<Ciphertext>> c) {
string s;
for (uint32_t i = 0; i < c.size(); i++) {
for (uint32_t j = 0; j < c[i].size(); j++) {
s.append(serialize_ciphertext(c[i][j]));
}
}
return s;
}