Adding identity element checks and ensuring non-zero scalar selection

src/messages.rs

@@ -28,6 +28,14 @@ pub struct RegistrationRequest<CS: CipherSuite> {
     pub(crate) alpha: CS::Group,
 }
 
+impl<CS: CipherSuite> RegistrationRequest<CS> {
+    /// Only used for testing purposes
+    #[cfg(test)]
+    pub fn get_alpha_for_testing(&self) -> CS::Group {
+        self.alpha
+    }
+}
+
 // Cannot be derived because it would require for CS to be Clone.
 impl<CS: CipherSuite> Clone for RegistrationRequest<CS> {
     fn clone(&self) -> Self {
@@ -49,6 +57,11 @@ impl<CS: CipherSuite> RegistrationRequest<CS> {
         // correct subgroup
         let arr = GenericArray::from_slice(checked_slice);
         let alpha = CS::Group::from_element_slice(arr)?;
+
+        // Throw an error if the identity group element is encountered
+        if alpha.is_identity() {
+            return Err(PakeError::IdentityGroupElementError.into());
+        }
         Ok(Self { alpha })
     }
 }
@@ -91,6 +104,13 @@ impl<CS: CipherSuite> RegistrationResponse<CS> {
         // correct subgroup
         let arr = GenericArray::from_slice(&checked_slice[..elem_len]);
         let beta = CS::Group::from_element_slice(arr)?;
+
+        // Throw an error if the identity group element is encountered
+        if beta.is_identity() {
+            return Err(PakeError::IdentityGroupElementError.into());
+        }
+
+        // Ensure that public key is valid
         let server_s_pk = KeyPair::<CS::Group>::check_public_key(PublicKey::from_bytes(
             &checked_slice[elem_len..],
         )?)?;
@@ -188,6 +208,11 @@ impl<CS: CipherSuite> CredentialRequest<CS> {
         let arr = GenericArray::from_slice(&checked_slice[..elem_len]);
         let alpha = CS::Group::from_element_slice(arr)?;
 
+        // Throw an error if the identity group element is encountered
+        if alpha.is_identity() {
+            return Err(PakeError::IdentityGroupElementError.into());
+        }
+
         let ke1_message =
             <CS::KeyExchange as KeyExchange<CS::Hash, CS::Group>>::KE1Message::from_bytes::<CS>(
                 &checked_slice[elem_len..],
@@ -258,6 +283,11 @@ impl<CS: CipherSuite> CredentialResponse<CS> {
         let arr = GenericArray::from_slice(beta_bytes);
         let beta = CS::Group::from_element_slice(arr)?;
 
+        // Throw an error if the identity group element is encountered
+        if beta.is_identity() {
+            return Err(PakeError::IdentityGroupElementError.into());
+        }
+
         let unchecked_server_s_pk =
             PublicKey::from_bytes(&checked_slice[elem_len..elem_len + key_len])?;
         let server_s_pk = KeyPair::<CS::Group>::check_public_key(unchecked_server_s_pk)?;