From 98a33dad0d2ceaff3053d27ca6d12e05b840b2ef Mon Sep 17 00:00:00 2001
From: Sam Hadow <sam.hadow@inbox.lv>
Date: Wed, 30 Apr 2025 15:31:29 +0200
Subject: [PATCH] asymmetric encryption

---
 src/dghv_asym.rs | 45 +++++++++++++++++++++++++++++++++++++++++++++
 src/utils.rs     |  2 +-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/src/dghv_asym.rs b/src/dghv_asym.rs
index a4a2a9a..ddcc457 100644
--- a/src/dghv_asym.rs
+++ b/src/dghv_asym.rs
@@ -1,4 +1,8 @@
 use crate::dghv::{encrypt_bit, generate_secret_key};
+use crate::utils::generate_random_integer;
+use rand::rngs::StdRng;
+use rand::Rng;
+use rand::SeedableRng;
 use rug::Integer;
 
 pub struct PublicKey {
@@ -29,9 +33,35 @@ pub fn generate_keys(gamma: u32, eta: u32, rho: u32, theta: usize) -> (PrivateKe
     (PrivateKey { p }, PublicKey { xs })
 }
 
+/// c = (m + 2*r + sum(b_i * x_i) for i>0 ) mod x0
+/// x0 = largest public element, the x_i are randomly chosen
+pub fn encrypt_bit_asym(m: u8, pk: &PublicKey, rho: u32) -> Integer {
+    assert!(m == 0 || m == 1, "Message bit must be 0 or 1");
+    let mut rng = StdRng::from_os_rng();
+    let x0 = &pk.xs[0];
+
+    // random x_i
+    let mut sum = Integer::from(0);
+    for x in pk.xs.iter().skip(1) {
+        if rng.random_bool(0.5) {
+            sum += x;
+        }
+    }
+
+    // noise
+    let r = generate_random_integer(rho);
+    let mut c = Integer::from(m);
+    c += Integer::from(2) * r;
+    c += sum;
+
+    c %= x0;
+    c
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::decrypt_bit;
 
     #[test]
     fn test_key_generation_properties() {
@@ -51,4 +81,19 @@ mod tests {
             assert!(pk.xs[0] >= *xi);
         }
     }
+
+    #[test]
+    fn test_encrypt_decrypt_bit() {
+        let eta: u32 = 1024;
+        let gamma: u32 = 2048;
+        let theta: usize = 128;
+        let rho: u32 = 128;
+        let (sk, pk) = generate_keys(gamma, eta, rho, theta);
+
+        for &m in &[0u8, 1u8] {
+            let c = encrypt_bit_asym(m, &pk, rho);
+            let m2 = decrypt_bit(&c, &sk.p);
+            assert_eq!(m, m2);
+        }
+    }
 }
diff --git a/src/utils.rs b/src/utils.rs
index 582db77..91effc4 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -6,7 +6,7 @@ use rug::Integer;
 pub fn generate_random_odd_integer(num_bits: u32) -> Integer {
     let mut rng = StdRng::from_os_rng();
     let mut x = Integer::from(1);
-    for _ in 1..(num_bits-1) {
+    for _ in 1..(num_bits - 1) {
         x <<= 1;
         x += rng.random_range(0..=1);
     }