Add a canonical way to get an id for Attestation and Certificate (#448)

* add hash() method on Attestation and Certificate

* clippy

nodes/nomos-node/src/bridges/mod.rs

@@ -150,7 +150,7 @@ where
                 &mempool_channel,
                 res_tx,
                 payload.unwrap_or_default(),
-                |cert| cert.blob(),
+                |cert| cert.hash(),
             )
             .await
             {

nodes/nomos-node/src/main.rs

@@ -107,5 +107,5 @@ fn main() -> Result<()> {
 
 fn cert_id(cert: &Certificate) -> <Blob as blob::Blob>::Hash {
     use certificate::Certificate;
-    cert.blob()
+    cert.hash()
 }

nomos-core/src/da/attestation/mod.rs

@@ -4,5 +4,6 @@ use bytes::Bytes;
 pub trait Attestation {
     type Blob: Blob;
     fn blob(&self) -> <Self::Blob as Blob>::Hash;
+    fn hash(&self) -> <Self::Blob as Blob>::Hash;
     fn as_bytes(&self) -> Bytes;
 }

nomos-core/src/da/certificate/mod.rs

@@ -6,7 +6,7 @@ use bytes::Bytes;
 pub trait Certificate {
     type Blob: Blob;
     fn blob(&self) -> <Self::Blob as Blob>::Hash;
-
+    fn hash(&self) -> <Self::Blob as Blob>::Hash;
     fn as_bytes(&self) -> Bytes;
 }
 

nomos-da/full-replication/src/lib.rs

@@ -1,6 +1,6 @@
 // internal
 use nomos_core::da::{
-    attestation,
+    attestation::{self, Attestation as _},
     blob::{self, BlobHasher},
     certificate, DaProtocol,
 };
@@ -120,6 +120,11 @@ impl attestation::Attestation for Attestation {
     fn blob(&self) -> [u8; 32] {
         self.blob
     }
+
+    fn hash(&self) -> <Self::Blob as blob::Blob>::Hash {
+        hash([self.blob, self.voter].concat())
+    }
+
     fn as_bytes(&self) -> Bytes {
         wire::serialize(self)
             .expect("Attestation shouldn't fail to be serialized")
@@ -145,6 +150,17 @@ impl certificate::Certificate for Certificate {
         self.attestations[0].blob
     }
 
+    fn hash(&self) -> <Self::Blob as blob::Blob>::Hash {
+        let mut input = self
+            .attestations
+            .iter()
+            .map(|a| a.hash())
+            .collect::<Vec<_>>();
+        // sort to make the hash deterministic
+        input.sort();
+        hash(input.concat())
+    }
+
     fn as_bytes(&self) -> Bytes {
         wire::serialize(self)
             .expect("Certificate shouldn't fail to be serialized")
@@ -208,3 +224,11 @@ impl DaProtocol for FullReplication<AbsoluteNumber<Attestation, Certificate>> {
             .can_build(&certificate.attestations)
     }
 }
+
+fn hash(item: impl AsRef<[u8]>) -> [u8; 32] {
+    let mut hasher = Blake2bVar::new(32).unwrap();
+    hasher.update(item.as_ref());
+    let mut output = [0; 32];
+    hasher.finalize_variable(&mut output).unwrap();
+    output
+}