From 2b34669d3353d4b451489b9e9f57e2258e8016f2 Mon Sep 17 00:00:00 2001
From: Daniel Sanchez Quiros <sanchez.quiros.daniel@gmail.com>
Date: Wed, 17 Apr 2024 13:04:36 +0200
Subject: [PATCH] Implement verifier new Implement verifier check column

---
 nomos-da/kzgrs-backend/Cargo.toml      |  9 ++--
 nomos-da/kzgrs-backend/src/verifier.rs | 75 +++++++++++++++++++++++++-
 2 files changed, 79 insertions(+), 5 deletions(-)

diff --git a/nomos-da/kzgrs-backend/Cargo.toml b/nomos-da/kzgrs-backend/Cargo.toml
index d5cb4281..52b6855a 100644
--- a/nomos-da/kzgrs-backend/Cargo.toml
+++ b/nomos-da/kzgrs-backend/Cargo.toml
@@ -6,15 +6,18 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-blake2 = "0.10"
+ark-ff = "0.4"
 ark-serialize = "0.4.2"
 ark-poly = "0.4.2"
+blake2 = "0.10"
+blst = "0.3.11"
+itertools = "0.12"
 kzgrs = { path = "../kzgrs" }
+num-bigint = "0.4.4"
 rand = "0.8.5"
 once_cell = "1.19"
 sha3 = "0.10"
 
 [dev-dependencies]
 rand = "0.8"
-itertools = "0.12"
-ark-ff = "0.4"
+
diff --git a/nomos-da/kzgrs-backend/src/verifier.rs b/nomos-da/kzgrs-backend/src/verifier.rs
index 821bfd76..65092926 100644
--- a/nomos-da/kzgrs-backend/src/verifier.rs
+++ b/nomos-da/kzgrs-backend/src/verifier.rs
@@ -1,7 +1,21 @@
-use crate::common::{build_attestation_message, Column};
-use kzgrs::{Commitment, Proof};
+// std
+
+// crates
+use blst::min_sig::{PublicKey, SecretKey, Signature};
+use itertools::Itertools;
+use num_bigint::BigUint;
 use sha3::{Digest, Sha3_256};
 
+// internal
+use crate::common::{build_attestation_message, hash_column_and_commitment, Column};
+use crate::encoder::DaEncoderParams;
+use crate::global::{DOMAIN, GLOBAL_PARAMETERS};
+use kzgrs::common::field_element_from_bytes_le;
+use kzgrs::{
+    bytes_to_polynomial, commit_polynomial, verify_element_proof, Commitment, FieldElement, Proof,
+    BYTES_PER_FIELD_ELEMENT,
+};
+
 pub struct DaBlob {
     column: Column,
     column_commitment: Commitment,
@@ -22,3 +36,60 @@ impl DaBlob {
         hasher.finalize().as_slice().to_vec()
     }
 }
+
+pub struct DaVerifier {
+    // TODO: substitute this for an abstraction to sign things over
+    sk: SecretKey,
+    index: usize,
+}
+
+impl DaVerifier {
+    pub fn new(sk: SecretKey, nodes_public_keys: &[PublicKey]) -> Self {
+        // TODO: `is_sorted` is experimental, and by contract `nodes_public_keys` should be shorted
+        // but not sure how we could enforce it here without re-sorting anyway.
+        // assert!(nodes_public_keys.is_sorted());
+        let self_pk = sk.sk_to_pk();
+        let (index, _) = nodes_public_keys
+            .iter()
+            .find_position(|&pk| pk == &self_pk)
+            .expect("Self pk should be registered");
+        Self { sk, index }
+    }
+
+    fn verify_column(
+        column: &Column,
+        column_commitment: &Commitment,
+        aggregated_column_commitment: &Commitment,
+        aggregated_column_proof: &Proof,
+        index: usize,
+    ) -> bool {
+        // 1. compute commitment for column
+        let Ok((_, polynomial)) =
+            bytes_to_polynomial::<BYTES_PER_FIELD_ELEMENT>(column.as_bytes().as_slice(), *DOMAIN)
+        else {
+            return false;
+        };
+        let Ok(computed_column_commitment) = commit_polynomial(&polynomial, &GLOBAL_PARAMETERS)
+        else {
+            return false;
+        };
+        // 2. if computed column commitment != column commitment, fail
+        if &computed_column_commitment != column_commitment {
+            return false;
+        }
+        // 3. compute column hash
+        let column_hash = hash_column_and_commitment::<
+            { DaEncoderParams::MAX_BLS12_381_ENCODING_CHUNK_SIZE },
+        >(column, column_commitment);
+        // 4. check proof with commitment and proof over the aggregated column commitment
+        let element = field_element_from_bytes_le(column_hash.as_slice());
+        verify_element_proof(
+            index,
+            &element,
+            aggregated_column_commitment,
+            aggregated_column_proof,
+            *DOMAIN,
+            &GLOBAL_PARAMETERS,
+        )
+    }
+}