refactor(core): decouple encoder from mpz (#692)

* WIP: Adding new encoding logic...

* feat: add new encoder

* add feedback

* rename conversions

Cargo.toml

@@ -110,6 +110,7 @@ http = { version = "1.1" }
 http-body-util = { version = "0.1" }
 hyper = { version = "1.1" }
 hyper-util = { version = "0.1" }
+itybity = { version = "0.2" }
 k256 = { version = "0.13" }
 log = { version = "0.4" }
 once_cell = { version = "1.19" }

crates/core/Cargo.toml

@@ -30,6 +30,7 @@ opaque-debug = { workspace = true }
 p256 = { workspace = true, features = ["serde"] }
 rand = { workspace = true }
 rand_core = { workspace = true }
+rand_chacha = { workspace = true }
 rs_merkle = { workspace = true, features = ["serde"] }
 rstest = { workspace = true, optional = true }
 serde = { workspace = true }
@@ -38,6 +39,7 @@ thiserror = { workspace = true }
 tiny-keccak = { version = "2.0", features = ["keccak"] }
 web-time = { workspace = true }
 webpki-roots = { workspace = true }
+itybity = { workspace = true }
 
 [dev-dependencies]
 bincode = { workspace = true }

crates/core/src/attestation/builder.rs

@@ -12,6 +12,7 @@ use crate::{
     request::Request,
     serialize::CanonicalSerialize,
     signing::SignatureAlgId,
+    transcript::encoding::EncoderSecret,
     CryptoProvider,
 };
 
@@ -25,7 +26,7 @@ pub struct Sign {
     server_ephemeral_key: Option<ServerEphemKey>,
     cert_commitment: ServerCertCommitment,
     encoding_commitment_root: Option<TypedHash>,
-    encoding_seed: Option<Vec<u8>>,
+    encoder_secret: Option<EncoderSecret>,
 }
 
 /// An attestation builder.
@@ -91,7 +92,7 @@ impl<'a> AttestationBuilder<'a, Accept> {
                 server_ephemeral_key: None,
                 cert_commitment,
                 encoding_commitment_root,
-                encoding_seed: None,
+                encoder_secret: None,
             },
         })
     }
@@ -110,9 +111,9 @@ impl AttestationBuilder<'_, Sign> {
         self
     }
 
-    /// Sets the encoding seed.
-    pub fn encoding_seed(&mut self, seed: Vec<u8>) -> &mut Self {
-        self.state.encoding_seed = Some(seed);
+    /// Sets the encoder secret.
+    pub fn encoder_secret(&mut self, secret: EncoderSecret) -> &mut Self {
+        self.state.encoder_secret = Some(secret);
         self
     }
 
@@ -125,7 +126,7 @@ impl AttestationBuilder<'_, Sign> {
             server_ephemeral_key,
             cert_commitment,
             encoding_commitment_root,
-            encoding_seed,
+            encoder_secret,
         } = self.state;
 
         let hasher = provider.hash.get(&hash_alg).map_err(|_| {
@@ -144,14 +145,14 @@ impl AttestationBuilder<'_, Sign> {
         })?;
 
         let encoding_commitment = if let Some(root) = encoding_commitment_root {
-            let Some(seed) = encoding_seed else {
+            let Some(secret) = encoder_secret else {
                 return Err(AttestationBuilderError::new(
                     ErrorKind::Field,
-                    "encoding commitment requested but seed was not set",
+                    "encoding commitment requested but encoder_secret was not set",
                 ));
             };
 
-            Some(EncodingCommitment { root, seed })
+            Some(EncodingCommitment { root, secret })
         } else {
             None
         };
@@ -246,7 +247,7 @@ mod test {
     use crate::{
         connection::{HandshakeData, HandshakeDataV1_2},
         fixtures::{
-            encoder_seed, encoding_provider, request_fixture, ConnectionFixture, RequestFixture,
+            encoder_secret, encoding_provider, request_fixture, ConnectionFixture, RequestFixture,
         },
         hash::Blake3,
         transcript::Transcript,
@@ -435,7 +436,7 @@ mod test {
 
         attestation_builder
             .connection_info(connection_info)
-            .encoding_seed(encoder_seed().to_vec());
+            .encoder_secret(encoder_secret());
 
         let err = attestation_builder.build(crypto_provider).err().unwrap();
         assert!(matches!(err.kind, ErrorKind::Field));
@@ -471,7 +472,7 @@ mod test {
 
         attestation_builder
             .server_ephemeral_key(server_ephemeral_key)
-            .encoding_seed(encoder_seed().to_vec());
+            .encoder_secret(encoder_secret());
 
         let err = attestation_builder.build(crypto_provider).err().unwrap();
         assert!(matches!(err.kind, ErrorKind::Field));

crates/core/src/fixtures.rs

@@ -2,7 +2,7 @@
 
 mod provider;
 
-pub use provider::ChaChaProvider;
+pub use provider::FixtureEncodingProvider;
 
 use hex::FromHex;
 use p256::ecdsa::SigningKey;
@@ -17,7 +17,7 @@ use crate::{
     request::{Request, RequestConfig},
     signing::SignatureAlgId,
     transcript::{
-        encoding::{EncodingProvider, EncodingTree},
+        encoding::{EncoderSecret, EncodingProvider, EncodingTree},
         Transcript, TranscriptCommitConfigBuilder,
     },
     CryptoProvider,
@@ -131,12 +131,26 @@ impl ConnectionFixture {
 
 /// Returns an encoding provider fixture.
 pub fn encoding_provider(tx: &[u8], rx: &[u8]) -> impl EncodingProvider {
-    ChaChaProvider::new(encoder_seed(), Transcript::new(tx, rx))
+    let secret = encoder_secret();
+    FixtureEncodingProvider::new(&secret, Transcript::new(tx, rx))
 }
 
-/// Returns an encoder seed fixture.
-pub fn encoder_seed() -> [u8; 32] {
-    [0u8; 32]
+/// Seed fixture.
+const SEED: [u8; 32] = [0; 32];
+
+/// Delta fixture.
+const DELTA: [u8; 16] = [1; 16];
+
+/// Returns an encoder secret fixture.
+pub fn encoder_secret() -> EncoderSecret {
+    EncoderSecret::new(SEED, DELTA)
+}
+
+/// Returns a tampered encoder secret fixture.
+pub fn encoder_secret_tampered_seed() -> EncoderSecret {
+    let mut seed = SEED;
+    seed[0] += 1;
+    EncoderSecret::new(seed, DELTA)
 }
 
 /// Returns a notary signing key fixture.
@@ -205,7 +219,7 @@ pub fn attestation_fixture(
     request: Request,
     connection: ConnectionFixture,
     signature_alg: SignatureAlgId,
-    encoding_seed: Vec<u8>,
+    secret: EncoderSecret,
 ) -> Attestation {
     let ConnectionFixture {
         connection_info,
@@ -237,7 +251,7 @@ pub fn attestation_fixture(
     attestation_builder
         .connection_info(connection_info)
         .server_ephemeral_key(server_ephemeral_key)
-        .encoding_seed(encoding_seed);
+        .encoder_secret(secret);
 
     attestation_builder.build(&provider).unwrap()
 }

crates/core/src/fixtures/provider.rs

@@ -1,27 +1,25 @@
-use mpz_garble_core::ChaChaEncoder;
-
 use crate::transcript::{
-    encoding::{Encoder, EncodingProvider},
+    encoding::{new_encoder, Encoder, EncoderSecret, EncodingProvider},
     Direction, Idx, Transcript,
 };
 
-/// A ChaCha encoding provider fixture.
-pub struct ChaChaProvider {
-    encoder: ChaChaEncoder,
+/// A encoding provider fixture.
+pub struct FixtureEncodingProvider {
+    encoder: Box<dyn Encoder>,
     transcript: Transcript,
 }
 
-impl ChaChaProvider {
-    /// Creates a new ChaCha encoding provider.
-    pub(crate) fn new(seed: [u8; 32], transcript: Transcript) -> Self {
+impl FixtureEncodingProvider {
+    /// Creates a new encoding provider fixture.
+    pub(crate) fn new(secret: &EncoderSecret, transcript: Transcript) -> Self {
         Self {
-            encoder: ChaChaEncoder::new(seed),
+            encoder: Box::new(new_encoder(secret)),
             transcript,
         }
     }
 }
 
-impl EncodingProvider for ChaChaProvider {
+impl EncodingProvider for FixtureEncodingProvider {
     fn provide_encoding(&self, direction: Direction, idx: &Idx) -> Option<Vec<u8>> {
         let seq = self.transcript.get(direction, idx)?;
         Some(self.encoder.encode_subsequence(direction, &seq))

crates/core/src/request.rs

@@ -97,7 +97,7 @@ mod test {
     use crate::{
         connection::{ServerCertOpening, TranscriptLength},
         fixtures::{
-            attestation_fixture, encoder_seed, encoding_provider, request_fixture,
+            attestation_fixture, encoder_secret, encoding_provider, request_fixture,
             ConnectionFixture, RequestFixture,
         },
         hash::{Blake3, Hash, HashAlgId},
@@ -122,7 +122,7 @@ mod test {
             request.clone(),
             connection,
             SignatureAlgId::SECP256K1,
-            encoder_seed().to_vec(),
+            encoder_secret(),
         );
 
         assert!(request.validate(&attestation).is_ok())
@@ -144,7 +144,7 @@ mod test {
             request.clone(),
             connection,
             SignatureAlgId::SECP256K1,
-            encoder_seed().to_vec(),
+            encoder_secret(),
         );
 
         request.signature_alg = SignatureAlgId::SECP256R1;
@@ -169,7 +169,7 @@ mod test {
             request.clone(),
             connection,
             SignatureAlgId::SECP256K1,
-            encoder_seed().to_vec(),
+            encoder_secret(),
         );
 
         request.hash_alg = HashAlgId::SHA256;
@@ -194,7 +194,7 @@ mod test {
             request.clone(),
             connection,
             SignatureAlgId::SECP256K1,
-            encoder_seed().to_vec(),
+            encoder_secret(),
         );
 
         let ConnectionFixture {
@@ -229,7 +229,7 @@ mod test {
             request.clone(),
             connection,
             SignatureAlgId::SECP256K1,
-            encoder_seed().to_vec(),
+            encoder_secret(),
         );
 
         request.encoding_commitment_root = Some(TypedHash {

crates/core/src/transcript.rs

@@ -52,11 +52,6 @@ pub use proof::{
     TranscriptProof, TranscriptProofBuilder, TranscriptProofBuilderError, TranscriptProofError,
 };
 
-/// Sent data transcript ID.
-pub static TX_TRANSCRIPT_ID: &str = "tx";
-/// Received data transcript ID.
-pub static RX_TRANSCRIPT_ID: &str = "rx";
-
 /// A transcript contains all the data communicated over a TLS connection.
 #[derive(Clone, Serialize, Deserialize)]
 pub struct Transcript {
@@ -588,17 +583,6 @@ impl Subsequence {
 #[error("invalid subsequence: {0}")]
 pub struct InvalidSubsequence(&'static str);
 
-/// Returns the value ID for each byte in the provided range set.
-#[doc(hidden)]
-pub fn get_value_ids(direction: Direction, idx: &Idx) -> impl Iterator<Item = String> + '_ {
-    let id = match direction {
-        Direction::Sent => TX_TRANSCRIPT_ID,
-        Direction::Received => RX_TRANSCRIPT_ID,
-    };
-
-    idx.iter().map(move |idx| format!("{}/{}", id, idx))
-}
-
 mod validation {
     use super::*;
 

crates/core/src/transcript/encoding.rs

@@ -8,6 +8,7 @@ mod proof;
 mod provider;
 mod tree;
 
+pub use encoder::EncoderSecret;
 pub(crate) use encoder::{new_encoder, Encoder};
 pub use proof::{EncodingProof, EncodingProofError};
 pub use provider::EncodingProvider;
@@ -32,7 +33,7 @@ pub struct EncodingCommitment {
     /// Merkle root of the encoding commitments.
     pub root: TypedHash,
     /// Seed used to generate the encodings.
-    pub seed: Vec<u8>,
+    pub secret: EncoderSecret,
 }
 
 impl_domain_separator!(EncodingCommitment);