draft new ciphertext api

ferveo-python/ferveo/__init__.py

@@ -9,6 +9,7 @@
     Transcript,
     Dkg,
     Ciphertext,
+    CiphertextHeader,
     DecryptionShareSimple,
     DecryptionSharePrecomputed,
     AggregatedTranscript,

ferveo-python/ferveo/__init__.pyi

@@ -126,6 +126,15 @@ class Ciphertext:
     def __bytes__(self) -> bytes:
         ...
 
+@final
+class CiphertextHeader:
+    @staticmethod
+    def from_bytes(data: bytes) -> Ciphertext:
+        ...
+
+    def __bytes__(self) -> bytes:
+        ...
+
 
 @final
 class DecryptionShareSimple:

ferveo/src/api.rs

@@ -12,7 +12,7 @@ use serde::{Deserialize, Serialize};
 use serde_with::serde_as;
 pub use tpke::api::{
     prepare_combine_simple, share_combine_precomputed, share_combine_simple,
-    Ciphertext, Fr, G1Affine, G1Prepared, SecretBox, E,
+    Fr, G1Affine, G1Prepared, G2Affine, SecretBox, E,
 };
 
 pub type PublicKey = ferveo_common::PublicKey<E>;
@@ -55,7 +55,7 @@ pub fn encrypt(
 ) -> Result<Ciphertext> {
     let mut rng = rand::thread_rng();
     let ciphertext = tpke::api::encrypt(message, aad, &pubkey.0, &mut rng)?;
-    Ok(ciphertext)
+    Ok(Ciphertext(ciphertext))
 }
 
 pub fn decrypt_with_shared_secret(
@@ -65,14 +65,43 @@ pub fn decrypt_with_shared_secret(
 ) -> Result<Vec<u8>> {
     let dkg_public_params = DkgPublicParameters::default();
     tpke::api::decrypt_with_shared_secret(
-        ciphertext,
+        &ciphertext.0,
         aad,
         &shared_secret.0,
         &dkg_public_params.g1_inv,
     )
     .map_err(Error::from)
 }
 
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Eq)]
+pub struct Ciphertext(pub(crate) tpke::api::Ciphertext);
+
+impl Ciphertext {
+    pub fn header(&self) -> CiphertextHeader {
+        let ciphertext_hash = self.0.ciphertext_hash();
+        CiphertextHeader {
+            commitment: self.0.commitment,
+            auth_tag: self.0.auth_tag,
+            ciphertext_hash,
+        }
+    }
+
+    pub fn payload(&self) -> Vec<u8> {
+        // TODO: Do we want to return a Vec<u8> here or rather obfuscate the type with a newtype/struct?
+        self.0.ciphertext.clone()
+    }
+}
+
+#[serde_as]
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
+pub struct CiphertextHeader {
+    #[serde_as(as = "serialization::SerdeAs")]
+    commitment: G1Affine,
+    #[serde_as(as = "serialization::SerdeAs")]
+    auth_tag: G2Affine,
+    ciphertext_hash: [u8; 32],
+}
+
 /// The ferveo variant to use for the decryption share derivation.
 #[derive(
     PartialEq, Eq, Debug, Serialize, Deserialize, Copy, Clone, PartialOrd,
@@ -297,7 +326,7 @@ impl AggregatedTranscript {
             .take(dkg.0.dkg_params.shares_num as usize)
             .collect();
         self.0.make_decryption_share_simple_precomputed(
-            ciphertext,
+            &ciphertext.0,
             aad,
             &validator_keypair.decryption_key,
             dkg.0.me.share_index,
@@ -314,7 +343,7 @@ impl AggregatedTranscript {
         validator_keypair: &Keypair,
     ) -> Result<DecryptionShareSimple> {
         let share = self.0.make_decryption_share_simple(
-            ciphertext,
+            &ciphertext.0,
             aad,
             &validator_keypair.decryption_key,
             dkg.0.me.share_index,
@@ -458,14 +487,10 @@ mod test_ferveo_api {
             // In the meantime, the client creates a ciphertext and decryption request
             let msg = "my-msg".as_bytes().to_vec();
             let aad: &[u8] = "my-aad".as_bytes();
-            let rng = &mut thread_rng();
-            let ciphertext = tpke::api::encrypt(
-                SecretBox::new(msg.clone()),
-                aad,
-                &dkg_public_key.0,
-                rng,
-            )
-            .unwrap();
+            let _rng = &mut thread_rng();
+            let ciphertext =
+                encrypt(SecretBox::new(msg.clone()), aad, &dkg_public_key)
+                    .unwrap();
 
             // Having aggregated the transcripts, the validators can now create decryption shares
             let decryption_shares: Vec<_> =
@@ -557,14 +582,9 @@ mod test_ferveo_api {
             // In the meantime, the client creates a ciphertext and decryption request
             let msg = "my-msg".as_bytes().to_vec();
             let aad: &[u8] = "my-aad".as_bytes();
-            let rng = &mut thread_rng();
-            let ciphertext = tpke::api::encrypt(
-                SecretBox::new(msg.clone()),
-                aad,
-                &public_key.0,
-                rng,
-            )
-            .unwrap();
+            let _rng = &mut thread_rng();
+            let ciphertext =
+                encrypt(SecretBox::new(msg.clone()), aad, &public_key).unwrap();
 
             // Having aggregated the transcripts, the validators can now create decryption shares
             let decryption_shares: Vec<_> =

ferveo/src/bindings_python.rs

@@ -514,6 +514,22 @@ pub struct Ciphertext(api::Ciphertext);
 
 generate_bytes_serialization!(Ciphertext);
 
+#[pyclass(module = "ferveo")]
+#[derive(
+    Clone,
+    Debug,
+    PartialEq,
+    Eq,
+    Serialize,
+    Deserialize,
+    derive_more::From,
+    derive_more::AsRef,
+    derive_more::Into,
+)]
+pub struct CiphertextHeader(api::CiphertextHeader);
+
+generate_bytes_serialization!(CiphertextHeader);
+
 #[pyclass(module = "ferveo")]
 #[derive(Clone, derive_more::AsRef, derive_more::From)]
 pub struct DecryptionShareSimple(api::DecryptionShareSimple);
@@ -631,6 +647,7 @@ pub fn make_ferveo_py_module(py: Python<'_>, m: &PyModule) -> PyResult<()> {
     m.add_class::<Transcript>()?;
     m.add_class::<Dkg>()?;
     m.add_class::<Ciphertext>()?;
+    m.add_class::<CiphertextHeader>()?;
     m.add_class::<DecryptionShareSimple>()?;
     m.add_class::<DecryptionSharePrecomputed>()?;
     m.add_class::<AggregatedTranscript>()?;

tpke/src/api.rs

@@ -3,6 +3,7 @@
 pub type E = ark_bls12_381::Bls12_381;
 pub type G1Prepared = <E as ark_ec::pairing::Pairing>::G1Prepared;
 pub type G1Affine = <E as ark_ec::pairing::Pairing>::G1Affine;
+pub type G2Affine = <E as ark_ec::pairing::Pairing>::G2Affine;
 pub type Fr = ark_bls12_381::Fr;
 pub type PrivateKey = ark_bls12_381::G2Affine;
 pub type Result<T> = crate::Result<T>;

tpke/src/ciphertext.rs

@@ -55,6 +55,10 @@ impl<E: Pairing> Ciphertext<E> {
             + self.auth_tag.serialized_size(Compress::No)
             + self.ciphertext.len()
     }
+
+    pub fn ciphertext_hash(&self) -> [u8; 32] {
+        sha256(&self.ciphertext)
+    }
 }
 
 pub fn encrypt<E: Pairing>(
@@ -165,11 +169,11 @@ pub fn decrypt_with_shared_secret<E: Pairing>(
     decrypt_with_shared_secret_unchecked(ciphertext, shared_secret)
 }
 
-fn sha256(input: &[u8]) -> Vec<u8> {
+fn sha256(input: &[u8]) -> [u8; 32] {
     let mut hasher = Sha256::new();
     hasher.update(input);
     let result = hasher.finalize();
-    result.to_vec()
+    result.into()
 }
 
 pub fn shared_secret_to_chacha<E: Pairing>(