TLev encryption & decryption

README.md

@@ -1,7 +1,7 @@
 # fhe-study
 Implementations from scratch done while studying some FHE papers; do not use in production.
 
-- `arith`: contains $\mathbb{Z}_q$, $R_q=\mathbb{Z}_q[X]/(X^N+1)$, $R=\mathbb{Z}[X]/(X^N+1)$, $\mathbb{T}_{Q}[X]/(X^N +1)$ arithmetic implementations, together with the NTT implementation.
+- `arith`: contains $\mathbb{Z}_q$, $R_q=\mathbb{Z}_q[X]/(X^N+1)$, $R=\mathbb{Z}[X]/(X^N+1)$, $\mathbb{T}_Q[X]/(X^N +1)$ arithmetic implementations, together with the NTT implementation.
 - `gfhe`: (gfhe=generalized-fhe) contains the structs and logic for RLWE, GLWE, GLev, GGSW, RGSW cryptosystems, and modulus switching and key switching methods, which can be used by concrete FHE schemes.
 - `bfv`: https://eprint.iacr.org/2012/144.pdf scheme implementation
 - `ckks`: https://eprint.iacr.org/2016/421.pdf scheme implementation

tfhe/src/lib.rs

@@ -5,4 +5,5 @@
 #![allow(clippy::upper_case_acronyms)]
 #![allow(dead_code)] // TMP
 
+pub mod tlev;
 pub mod tlwe;

tfhe/src/tlev.rs

@@ -0,0 +1,92 @@
+use anyhow::Result;
+use rand::Rng;
+use std::array;
+use std::ops::{Add, Mul};
+
+use arith::{Ring, Rq, Tn, T64, TR};
+
+use crate::tlwe::{PublicKey, SecretKey, TLWE};
+
+#[derive(Clone, Debug)]
+pub struct TLev<const K: usize>(pub(crate) Vec<TLWE<K>>);
+
+impl<const K: usize> TLev<K> {
+    pub fn encode<const T: u64>(m: &Rq<T, 1>) -> Tn<1> {
+        let coeffs = m.coeffs();
+        Tn(array::from_fn(|i| T64(coeffs[i].0)))
+    }
+    pub fn decode<const T: u64>(p: &Tn<1>) -> Rq<T, 1> {
+        Rq::<T, 1>::from_vec_u64(p.coeffs().iter().map(|c| c.0).collect())
+    }
+    pub fn encrypt(
+        mut rng: impl Rng,
+        beta: u32,
+        l: u32,
+        pk: &PublicKey<K>,
+        m: &Tn<1>,
+    ) -> Result<Self> {
+        let tlev: Vec<TLWE<K>> = (1..l + 1)
+            .map(|i| {
+                TLWE::<K>::encrypt(&mut rng, pk, &(*m * (u64::MAX / beta.pow(i as u32) as u64)))
+            })
+            .collect::<Result<Vec<_>>>()?;
+
+        Ok(Self(tlev))
+    }
+    pub fn encrypt_s(
+        mut rng: impl Rng,
+        beta: u32,
+        l: u32,
+        sk: &SecretKey<K>,
+        m: &Tn<1>,
+    ) -> Result<Self> {
+        let tlev: Vec<TLWE<K>> = (1..l + 1)
+            .map(|i| {
+                TLWE::<K>::encrypt_s(&mut rng, sk, &(*m * (u64::MAX / beta.pow(i as u32) as u64)))
+            })
+            .collect::<Result<Vec<_>>>()?;
+
+        Ok(Self(tlev))
+    }
+
+    pub fn decrypt(&self, sk: &SecretKey<K>, beta: u32) -> Tn<1> {
+        let pt = self.0[0].decrypt(sk);
+        pt.mul_div_round(beta as u64, u64::MAX)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use anyhow::Result;
+    use rand::distributions::Uniform;
+
+    use super::*;
+
+    #[test]
+    fn test_encrypt_decrypt() -> Result<()> {
+        const T: u64 = 2; // plaintext modulus
+        const K: usize = 16;
+        type S = TLev<K>;
+
+        let beta: u32 = 2;
+        let l: u32 = 16;
+
+        let mut rng = rand::thread_rng();
+
+        for _ in 0..200 {
+            let (sk, pk) = TLWE::<K>::new_key(&mut rng)?;
+
+            let msg_dist = Uniform::new(0_u64, T);
+            let m: Rq<T, 1> = Rq::rand_u64(&mut rng, msg_dist)?;
+            let p: Tn<1> = S::encode::<T>(&m); // plaintext
+
+            let c = S::encrypt(&mut rng, beta, l, &pk, &p)?;
+            let p_recovered = c.decrypt(&sk, beta);
+            let m_recovered = S::decode::<T>(&p_recovered);
+
+            assert_eq!(m.remodule::<T>(), m_recovered.remodule::<T>());
+        }
+
+        Ok(())
+    }
+}