feat(mpc-tls): improve error message for incorrect transcript config (#754)

* feat(mpc-tls): improve error message for incorrect transcript config

* rustfmt

---------

Co-authored-by: dan <themighty1@users.noreply.github.com>

crates/mpc-tls/src/config.rs

@@ -50,7 +50,7 @@ impl ConfigBuilder {
         let mut max_recv_online = self
             .max_recv_online
             .ok_or(ConfigBuilderError::UninitializedField("max_recv_online"))?;
-        let max_recv = self
+        let mut max_recv = self
             .max_recv
             .ok_or(ConfigBuilderError::UninitializedField("max_recv"))?;
 
@@ -61,6 +61,7 @@ impl ConfigBuilder {
         }
 
         max_recv_online += MIN_RECV;
+        max_recv += MIN_RECV;
 
         let max_sent_records = self
             .max_sent_records

crates/mpc-tls/src/follower.rs

@@ -135,6 +135,7 @@ impl MpcTlsFollower {
                 self.config.max_recv_records,
                 self.config.max_sent,
                 self.config.max_recv_online,
+                self.config.max_recv,
             )?;
 
             (keys, cf_vd, sf_vd)

crates/mpc-tls/src/leader.rs

@@ -169,6 +169,7 @@ impl MpcTlsLeader {
             self.config.max_recv_records,
             self.config.max_sent,
             self.config.max_recv_online,
+            self.config.max_recv,
         )?;
 
         self.state = State::Setup {

crates/mpc-tls/src/record_layer.rs

@@ -80,6 +80,18 @@ pub(crate) struct RecordLayer {
     state: State,
     /// Whether the record layer has started processing application data.
     started: bool,
+    /// Number of bytes sent.
+    sent: usize,
+    /// Number of bytes received and decrypted online.
+    recv_online: usize,
+    /// Number of bytes received.
+    recv: usize,
+    /// Maximum number of bytes sent.
+    max_sent: usize,
+    /// Maximum number of bytes received to be decrypted online.
+    max_recv_online: usize,
+    /// Maximum number of bytes received.
+    max_recv: usize,
 
     encrypt_buffer: Vec<EncryptOp>,
     decrypt_buffer: Vec<DecryptOp>,
@@ -99,6 +111,12 @@ impl RecordLayer {
             aes_ctr: AesCtr::new(role),
             state: State::Init,
             started: false,
+            sent: 0,
+            recv_online: 0,
+            recv: 0,
+            max_sent: 0,
+            max_recv_online: 0,
+            max_recv: 0,
             encrypt_buffer: Vec::new(),
             decrypt_buffer: Vec::new(),
             encrypted_buffer: VecDeque::new(),
@@ -114,6 +132,8 @@ impl RecordLayer {
     /// * `sent_records` - Number of sent records to allocate.
     /// * `recv_records` - Number of received records to allocate.
     /// * `sent_len` - Total length of sent records to allocate.
+    /// * `recv_len_online` - Total length of received records to be decrypted
+    ///   online.
     /// * `recv_len` - Total length of received records to allocate.
     pub(crate) fn alloc(
         &mut self,
@@ -121,6 +141,7 @@ impl RecordLayer {
         sent_records: usize,
         recv_records: usize,
         sent_len: usize,
+        recv_len_online: usize,
         recv_len: usize,
     ) -> Result<(), MpcTlsError> {
         let State::Init = self.state.take() else {
@@ -142,12 +163,12 @@ impl RecordLayer {
             .map_err(MpcTlsError::record_layer)?;
 
         decrypt
-            .alloc(vm, recv_records, recv_len)
+            .alloc(vm, recv_records, recv_len_online)
             .map_err(MpcTlsError::record_layer)?;
 
         let recv_otp = match self.role {
             Role::Leader => {
-                let mut recv_otp = vec![0u8; recv_len];
+                let mut recv_otp = vec![0u8; recv_len_online];
                 rand::rng().fill_bytes(&mut recv_otp);
 
                 Some(recv_otp)
@@ -157,6 +178,10 @@ impl RecordLayer {
 
         self.aes_ctr.alloc(vm)?;
 
+        self.max_sent += sent_len;
+        self.max_recv_online += recv_len_online;
+        self.max_recv += recv_len;
+
         self.state = State::Online {
             recv_otp,
             sent_records: Vec::new(),
@@ -267,9 +292,15 @@ impl RecordLayer {
     ) -> Result<(), MpcTlsError> {
         if self.encrypt_buffer.len() >= MAX_BUFFER_SIZE {
             return Err(MpcTlsError::peer("encrypt buffer is full"));
+        } else if self.sent + len > self.max_sent {
+            return Err(MpcTlsError::record_layer(format!(
+                "attempted to send more data than was configured, increase `max_sent` in the config: current={}, additional={}, max={}",
+                self.sent, len, self.max_sent
+            )));
         }
 
         let (seq, explicit_nonce, aad) = self.next_write(typ, version, len);
+        self.sent += len;
         self.encrypt_buffer.push(EncryptOp::new(
             seq,
             typ,
@@ -295,9 +326,15 @@ impl RecordLayer {
     ) -> Result<(), MpcTlsError> {
         if self.decrypt_buffer.len() >= MAX_BUFFER_SIZE {
             return Err(MpcTlsError::peer("decrypt buffer is full"));
+        } else if self.recv + ciphertext.len() > self.max_recv {
+            return Err(MpcTlsError::record_layer(format!(
+                "attempted to receive more data than was configured, increase `max_recv` in the config: current={}, additional={}, max={}",
+                self.recv, ciphertext.len(), self.max_recv
+            )));
         }
 
         let (seq, aad) = self.next_read(typ, version, ciphertext.len());
+        self.recv += ciphertext.len();
         self.decrypt_buffer.push(DecryptOp::new(
             seq,
             typ,
@@ -386,6 +423,18 @@ impl RecordLayer {
             return Ok(());
         }
 
+        if is_decrypting {
+            let decrypt_len: usize = decrypt_ops.iter().map(|op| op.ciphertext.len()).sum();
+            if self.recv_online + decrypt_len > self.max_recv_online {
+                return Err(MpcTlsError::record_layer(format!(
+                    "attempted to decrypt more data in the online phase than was configured, increase `max_recv_online` in the config: current={}, additional={}, max={}",
+                    self.recv_online, decrypt_len, self.max_recv_online
+                )));
+            } else {
+                self.recv_online += decrypt_len;
+            }
+        }
+
         debug!(
             "processing {} encrypt ops and {} decrypt ops",
             encrypt_ops.len(),