1use bin_rs::*;
  2use itertools::Itertools;
  3use rand::{thread_rng, RngCore};
  4
  5struct Location<T>(T, T);
  6
  7impl<T> Location<T> {
  8    fn new(x: T, y: T) -> Self {
  9        Location(x, y)
 10    }
 11
 12    fn x(&self) -> &T {
 13        &self.0
 14    }
 15    fn y(&self) -> &T {
 16        &self.1
 17    }
 18}
 19
 20fn should_meet(a: &Location<u8>, b: &Location<u8>, b_threshold: &u8) -> bool {
 21    let diff_x = a.x() - b.x();
 22    let diff_y = a.y() - b.y();
 23    let d_sq = &(&diff_x * &diff_x) + &(&diff_y * &diff_y);
 24
 25    d_sq.le(b_threshold)
 26}
 27
 28/// Calculates distance square between a's and b's location. Returns a boolean
 29/// indicating whether diatance sqaure is <= `b_threshold`.
 30fn should_meet_fhe(
 31    a: &Location<FheUint8>,
 32    b: &Location<FheUint8>,
 33    b_threshold: &FheUint8,
 34) -> FheBool {
 35    let diff_x = a.x() - b.x();
 36    let diff_y = a.y() - b.y();
 37    let d_sq = &(&diff_x * &diff_x) + &(&diff_y * &diff_y);
 38
 39    d_sq.le(b_threshold)
 40}
 41
 42// Even wondered who are the long distance friends (friends of friends or
 43// friends of friends of friends...) that live nearby ? But how do you find
 44// them? Surely no-one will simply reveal their exact location just because
 45// there's a slight chance that a long distance friend lives nearby.
 46//
 47// Here we write a simple application with two users `a` and `b`. User `a` wants
 48// to find (long distance) friends that live in their neighbourhood. User `b` is
 49// open to meeting new friends within some distance of their location. Both user
 50// `a` and `b` encrypt their location and upload to the server. User `b` also
 51// encrypts the distance square threshold within which they are interested in
 52// meeting new friends. The server calculates the square of the distance between
 53// user a's location and user b's location and returns encrypted boolean output
 54// indicating whether square of distance is <= user b's supplied distance square
 55// threshold. User `a` then comes online, downloads output ciphertext, produces
 56// their decryption share for user `b`, and uploads the decryption share to the
 57// server. User `b` comes online, downloads output ciphertext and user a's
 58// decryption share, produces their own decryption share, and then decrypts the
 59// encrypted boolean output. If the output is `True`, it indicates
 60// user `a` is within the distance square threshold defined by user `b`.
 61fn main() {
 62    set_parameter_set(ParameterSelector::NonInteractiveLTE2Party);
 63
 64    // set application's common reference seed
 65    let mut seed = [0u8; 32];
 66    thread_rng().fill_bytes(&mut seed);
 67    set_common_reference_seed(seed);
 68
 69    let no_of_parties = 2;
 70
 71    // Client Side //
 72
 73    // Generate client keys
 74    let cks = (0..no_of_parties).map(|_| gen_client_key()).collect_vec();
 75
 76    // We assign id 0 to client 0 and id 1 to client 1
 77    let a_id = 0;
 78    let b_id = 1;
 79    let user_a_secret = &cks[0];
 80    let user_b_secret = &cks[1];
 81
 82    // User a and b generate server key shares
 83    let a_server_key_share = gen_server_key_share(a_id, no_of_parties, user_a_secret);
 84    let b_server_key_share = gen_server_key_share(b_id, no_of_parties, user_b_secret);
 85
 86    // User a and b encrypt their locations
 87    let user_a_secret = &cks[0];
 88    let user_a_location = Location::new(50, 60);
 89    let user_a_enc =
 90        user_a_secret.encrypt(vec![*user_a_location.x(), *user_a_location.y()].as_slice());
 91
 92    let user_b_location = Location::new(50, 60);
 93    // User b also encrypts the distance sq threshold
 94    let user_b_threshold = 20;
 95    let user_b_enc = user_b_secret
 96        .encrypt(vec![*user_b_location.x(), *user_b_location.y(), user_b_threshold].as_slice());
 97
 98    // Server Side //
 99
100    // Both user a and b upload their private inputs and server key shares to
101    // the server in one shot message
102    let server_key = aggregate_server_key_shares(&vec![a_server_key_share, b_server_key_share]);
103    server_key.set_server_key();
104
105    // Server parses private inputs from user a and b
106    let user_a_location_enc = {
107        let c = user_a_enc.unseed::<Vec<Vec<u64>>>().key_switch(0);
108        Location::new(c.extract(0), c.extract(1))
109    };
110    let (user_b_location_enc, user_b_threshold_enc) = {
111        let c = user_b_enc.unseed::<Vec<Vec<u64>>>().key_switch(1);
112        (Location::new(c.extract(0), c.extract(1)), c.extract(2))
113    };
114
115    // run the circuit
116    let out_c = should_meet_fhe(
117        &user_a_location_enc,
118        &user_b_location_enc,
119        &user_b_threshold_enc,
120    );
121
122    // Client Side //
123
124    // user a comes online, downloads out_c, produces a decryption share, and
125    // uploads the decryption share to the server.
126    let a_dec_share = user_a_secret.gen_decryption_share(&out_c);
127
128    // user b comes online downloads user a's decryption share, generates their
129    // own decryption share, decrypts the output ciphertext. If the output is
130    // True, they contact user a to meet.
131    let b_dec_share = user_b_secret.gen_decryption_share(&out_c);
132    let out_bool =
133        user_b_secret.aggregate_decryption_shares(&out_c, &vec![b_dec_share, a_dec_share]);
134
135    assert_eq!(
136        out_bool,
137        should_meet(&user_a_location, &user_b_location, &user_b_threshold)
138    );
139
140    if out_bool {
141        println!("A lives nearby. B should meet A.");
142    } else {
143        println!("A lives too far away!")
144    }
145}