Verifiable encryption tz_21: Make XOF generic and refactor encryption scheme in a trait to remove code duplication

Signed-off-by: lovesh <lovesh.bond@gmail.com>

Author: lovesh

oblivious_transfer/src/base_ot/naor_pinkas_ot.rs

@@ -1,22 +1,19 @@
 //! OT based on the paper [Efficient oblivious transfer protocols](https://dl.acm.org/doi/10.5555/365411.365502).
 //! Protocol is described in section 3.1. Allows to run `m` instances of 1-of-n chosen message OTs.
 
+use crate::{configs::OTConfig, error::OTError, util::xor, Message};
 use ark_ec::{AffineRepr, CurveGroup, Group};
 use ark_ff::PrimeField;
 use ark_serialize::{CanonicalDeserialize, CanonicalSerialize};
 use ark_std::{cfg_into_iter, cfg_iter, log2, rand::RngCore, vec, vec::Vec, UniformRand};
 use digest::{ExtendableOutput, Update};
-use itertools::Itertools;
-
-use crate::{util::xor, Message};
 use dock_crypto_utils::msm::WindowTable;
+use itertools::Itertools;
+use sha3::Shake256;
 
 #[cfg(feature = "parallel")]
 use rayon::prelude::*;
 
-use crate::{configs::OTConfig, error::OTError};
-use sha3::Shake256;
-
 /// Setup for running multiple 1-of-n OTs
 #[derive(Clone, Debug, PartialEq, Eq, CanonicalSerialize, CanonicalDeserialize)]
 pub struct OTSenderSetup<G: AffineRepr> {

verifiable_encryption/Cargo.toml

@@ -17,12 +17,12 @@ serde.workspace = true
 serde_with.workspace = true
 zeroize.workspace = true
 dock_crypto_utils = { version = "0.20.0", default-features = false, path = "../utils" }
-sha3 = { version = "0.10.6", default-features = false }
 itertools.workspace = true
 secret_sharing_and_dkg = { version = "0.13.0", default-features = false, path = "../secret_sharing_and_dkg" }
 
 [dev-dependencies]
 blake2.workspace = true
+sha3 = { version = "0.10.6", default-features = false }
 ark-bls12-381.workspace = true
 ark-secp256r1 = { version = "^0.4.0", default-features = false }
 

verifiable_encryption/src/lib.rs

@@ -1,3 +1,5 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
 //! # Verifiable encryption schemes
 //!
 //! Verifiable encryption of discrete log(s) from the paper [Verifiable Encryption from MPC-in-the-Head](https://eprint.iacr.org/2021/1704.pdf).

verifiable_encryption/src/tz_21/dkgith.rs

@@ -0,0 +1,243 @@
+use crate::tz_21::seed_tree::SeedTree;
+use ark_ec::{AffineRepr, CurveGroup};
+use ark_serialize::{CanonicalDeserialize, CanonicalSerialize};
+use ark_std::{
+    cfg_into_iter, cfg_iter, cfg_iter_mut, fmt::Debug, rand::RngCore, vec::Vec, UniformRand,
+};
+use dock_crypto_utils::{
+    aliases::FullDigest,
+    elgamal::{BatchedHashedElgamalCiphertext, HashedElgamalCiphertext},
+    msm::WindowTable,
+};
+
+#[cfg(feature = "parallel")]
+use rayon::prelude::*;
+
+/// A list of Elgamal ciphertexts, one for each message. For each message, encryptor creates fresh
+/// randomness and a thus a new shared secret using Diffie-Hellman key exchange
+#[derive(Clone, Debug, Default, CanonicalSerialize, CanonicalDeserialize)]
+pub struct SimpleBatchElgamalCiphertext<G: AffineRepr>(Vec<HashedElgamalCiphertext<G>>);
+
+/// A trait implemented by schemes encrypting a batch of messages
+pub trait BatchCiphertext<G: AffineRepr>:
+    Sized + Clone + Default + Debug + Send + Sync + CanonicalSerialize + CanonicalDeserialize
+{
+    /// Randomness used in the encryption
+    type Randomness: Clone + Default + CanonicalSerialize + CanonicalDeserialize;
+
+    /// Create a new ciphertext for the batch of messages
+    fn new<D: FullDigest>(
+        msgs: &[G::ScalarField],
+        randomness: &Self::Randomness,
+        public_key: &WindowTable<G::Group>,
+        gen: &WindowTable<G::Group>,
+    ) -> Self;
+
+    fn batch_size(&self) -> usize;
+
+    /// Decrypt the ciphertext to get the message batch back
+    fn decrypt<D: FullDigest>(&self, secret_key: &G::ScalarField) -> Vec<G::ScalarField>;
+
+    /// Add 1 item each from the given `deltas` to a ciphertext
+    fn add_to_ciphertexts(&mut self, deltas: &[G::ScalarField]);
+
+    /// Multiply each ciphertext by the given multiplier `m`
+    fn multiply_with_ciphertexts(&mut self, m: &G::ScalarField);
+
+    /// Multiply the OTP (one time pad) with given `m` before applying the OTP
+    fn decrypt_after_multiplying_otp<D: FullDigest>(
+        &self,
+        m: &G::ScalarField,
+        secret_key: &G::ScalarField,
+    ) -> Vec<G::ScalarField>;
+
+    /// Get randomness for encryption deterministically. Used in DKGitH
+    fn get_randomness_from_seed_tree<
+        const NUM_PARTIES: usize,
+        const DEPTH: usize,
+        const NUM_TOTAL_NODES: usize,
+        const SEED_SIZE: usize,
+        D: FullDigest,
+    >(
+        seed_tree: &SeedTree<NUM_PARTIES, DEPTH, NUM_TOTAL_NODES, SEED_SIZE>,
+        party_index: u16,
+        witness_count: usize,
+    ) -> Self::Randomness;
+
+    /// Get randomness for encryption using the given random number generator. Used in RDKGitH
+    fn get_randomness_from_rng<R: RngCore>(rng: &mut R, witness_count: usize) -> Self::Randomness;
+
+    fn is_randomness_size_correct(randomness: &Self::Randomness, witness_count: usize) -> bool;
+}
+
+impl<G: AffineRepr> BatchCiphertext<G> for SimpleBatchElgamalCiphertext<G> {
+    /// A different random value is created for each message to be encrypted
+    type Randomness = Vec<G::ScalarField>;
+
+    fn new<D: FullDigest>(
+        msgs: &[G::ScalarField],
+        randomness: &Vec<G::ScalarField>,
+        public_key: &WindowTable<G::Group>,
+        gen: &WindowTable<G::Group>,
+    ) -> Self {
+        assert_eq!(msgs.len(), randomness.len());
+        Self(
+            cfg_into_iter!(msgs)
+                .zip(cfg_into_iter!(randomness))
+                .map(|(m, r)| {
+                    HashedElgamalCiphertext::<G>::new_given_randomness_and_window_tables::<D>(
+                        m, r, public_key, gen,
+                    )
+                })
+                .collect(),
+        )
+    }
+
+    fn batch_size(&self) -> usize {
+        self.0.len()
+    }
+
+    fn decrypt<D: FullDigest>(&self, secret_key: &G::ScalarField) -> Vec<G::ScalarField> {
+        cfg_into_iter!(0..self.batch_size())
+            .map(|i| self.0[i].decrypt::<D>(secret_key))
+            .collect()
+    }
+
+    fn add_to_ciphertexts(&mut self, deltas: &[G::ScalarField]) {
+        assert_eq!(deltas.len(), self.batch_size());
+        cfg_iter_mut!(self.0)
+            .zip(cfg_iter!(deltas))
+            .for_each(|(m, d)| {
+                m.encrypted += d;
+            })
+    }
+
+    fn multiply_with_ciphertexts(&mut self, m: &G::ScalarField) {
+        cfg_iter_mut!(self.0).for_each(|c| {
+            c.encrypted *= m;
+        })
+    }
+
+    fn decrypt_after_multiplying_otp<D: FullDigest>(
+        &self,
+        m: &G::ScalarField,
+        secret_key: &G::ScalarField,
+    ) -> Vec<G::ScalarField> {
+        cfg_into_iter!(0..self.batch_size())
+            .map(|i| {
+                let otp = HashedElgamalCiphertext::otp::<D>(
+                    (self.0[i].eph_pk * secret_key).into_affine(),
+                ) * m;
+                self.0[i].encrypted - otp
+            })
+            .collect()
+    }
+
+    fn get_randomness_from_seed_tree<
+        const NUM_PARTIES: usize,
+        const DEPTH: usize,
+        const NUM_TOTAL_NODES: usize,
+        const SEED_SIZE: usize,
+        D: FullDigest,
+    >(
+        seed_tree: &SeedTree<NUM_PARTIES, DEPTH, NUM_TOTAL_NODES, SEED_SIZE>,
+        party_index: u16,
+        witness_count: usize,
+    ) -> Self::Randomness {
+        cfg_into_iter!(0..witness_count)
+            .map(|k| {
+                seed_tree.get_leaf_as_finite_field_element::<G::ScalarField, D>(
+                    party_index,
+                    &(witness_count + k).to_le_bytes(),
+                )
+            })
+            .collect()
+    }
+
+    fn get_randomness_from_rng<R: RngCore>(rng: &mut R, witness_count: usize) -> Self::Randomness {
+        (0..witness_count)
+            .map(|_| G::ScalarField::rand(rng))
+            .collect()
+    }
+
+    fn is_randomness_size_correct(randomness: &Self::Randomness, witness_count: usize) -> bool {
+        randomness.len() == witness_count
+    }
+}
+
+impl<G: AffineRepr> BatchCiphertext<G> for BatchedHashedElgamalCiphertext<G> {
+    /// Only a single value is created and then OTPs are generated by "appending" counters for each message to be encrypted
+    type Randomness = G::ScalarField;
+
+    fn new<D: FullDigest>(
+        msgs: &[G::ScalarField],
+        randomness: &G::ScalarField,
+        public_key: &WindowTable<G::Group>,
+        gen: &WindowTable<G::Group>,
+    ) -> Self {
+        BatchedHashedElgamalCiphertext::new_given_randomness_and_window_tables::<D>(
+            msgs, randomness, public_key, gen,
+        )
+    }
+
+    fn batch_size(&self) -> usize {
+        self.batch_size()
+    }
+
+    fn decrypt<D: FullDigest>(&self, secret_key: &G::ScalarField) -> Vec<G::ScalarField> {
+        self.decrypt::<D>(secret_key)
+    }
+
+    fn add_to_ciphertexts(&mut self, deltas: &[G::ScalarField]) {
+        cfg_iter_mut!(self.encrypted)
+            .zip(cfg_into_iter!(deltas))
+            .for_each(|(e_j, s_j)| {
+                *e_j += s_j;
+            })
+    }
+
+    fn multiply_with_ciphertexts(&mut self, m: &G::ScalarField) {
+        cfg_iter_mut!(self.encrypted).for_each(|c| {
+            *c *= m;
+        })
+    }
+
+    fn decrypt_after_multiplying_otp<D: FullDigest>(
+        &self,
+        m: &G::ScalarField,
+        secret_key: &G::ScalarField,
+    ) -> Vec<G::ScalarField> {
+        let shared_secret = (self.eph_pk * secret_key).into_affine();
+        cfg_into_iter!(0..self.batch_size())
+            .map(|i| {
+                let otp = BatchedHashedElgamalCiphertext::otp::<D>(&shared_secret, i as u32) * m;
+                self.encrypted[i] - otp
+            })
+            .collect()
+    }
+
+    fn get_randomness_from_seed_tree<
+        const NUM_PARTIES: usize,
+        const DEPTH: usize,
+        const NUM_TOTAL_NODES: usize,
+        const SEED_SIZE: usize,
+        D: FullDigest,
+    >(
+        seed_tree: &SeedTree<NUM_PARTIES, DEPTH, NUM_TOTAL_NODES, SEED_SIZE>,
+        party_index: u16,
+        witness_count: usize,
+    ) -> Self::Randomness {
+        seed_tree.get_leaf_as_finite_field_element::<G::ScalarField, D>(
+            party_index,
+            &(witness_count + party_index as usize).to_le_bytes(),
+        )
+    }
+
+    fn get_randomness_from_rng<R: RngCore>(rng: &mut R, _witness_count: usize) -> Self::Randomness {
+        G::ScalarField::rand(rng)
+    }
+
+    fn is_randomness_size_correct(_randomness: &Self::Randomness, _witness_count: usize) -> bool {
+        true
+    }
+}

verifiable_encryption/src/tz_21/dkgith_batched_elgamal.rs

@@ -18,11 +18,13 @@
 //!
 //! More docs in the corresponding modules.
 
+// TODO: Replace asserts with error handling in non-test code.
+
 #[macro_use]
 pub mod util;
 
+pub mod seed_tree;
+
 pub mod dkgith;
-pub mod dkgith_batched_elgamal;
+pub mod encryption;
 pub mod rdkgith;
-pub mod rdkgith_batched_elgamal;
-pub mod seed_tree;