monero: only mask user features on new polyseed, not on decode

- This commit ensures a polyseed string that has unsupported features correctly errors on decode (rather than panic in debug build or return an incorrect successful response in prod build)
- Also avoids panicking when checksum calculation is unexpectedly wrong

Polyseed reference impl for feature masking:
- polyseed_create: https://github.com/tevador/polyseed/blob/b7c35bb3c6b91e481ecb04fc235eaff69c507fa1/src/polyseed.c#L61
- polyseed_decode: https://github.com/tevador/polyseed/blob/b7c35bb3c6b91e481ecb04fc235eaff69c507fa1/src/polyseed.c#L212

coins/monero/src/tests/seed.rs

@@ -7,7 +7,7 @@ use curve25519_dalek::scalar::Scalar;
 use crate::{
   hash,
   wallet::seed::{
-    Seed, SeedType,
+    Seed, SeedType, SeedError,
     classic::{self, trim_by_lang},
     polyseed,
   },
@@ -405,3 +405,12 @@ fn test_polyseed() {
     }
   }
 }
+
+#[test]
+fn test_invalid_polyseed() {
+  let seed = "include domain claim resemble urban hire lunch bird \
+    crucial fire best wife ring warm ignore model"
+    .into();
+  let res = Seed::from_string(Zeroizing::new(seed));
+  assert_eq!(res, Err(SeedError::UnsupportedFeatures));
+}

coins/monero/src/wallet/seed/polyseed.rs

@@ -179,6 +179,31 @@ fn valid_entropy(entropy: &Zeroizing<[u8; 32]>) -> bool {
   res.into()
 }
 
+fn from_internal(
+  language: Language,
+  masked_features: u8,
+  encoded_birthday: u16,
+  entropy: Zeroizing<[u8; 32]>,
+) -> Result<Polyseed, SeedError> {
+  if !polyseed_features_supported(masked_features) {
+    Err(SeedError::UnsupportedFeatures)?;
+  }
+
+  if !valid_entropy(&entropy) {
+    Err(SeedError::InvalidEntropy)?;
+  }
+
+  let mut res = Polyseed {
+    language,
+    birthday: encoded_birthday,
+    features: masked_features,
+    entropy,
+    checksum: 0,
+  };
+  res.checksum = poly_eval(&res.to_poly());
+  Ok(res)
+}
+
 impl Polyseed {
   // TODO: Clean this
   fn to_poly(&self) -> Poly {
@@ -226,20 +251,7 @@ impl Polyseed {
     birthday: u64,
     entropy: Zeroizing<[u8; 32]>,
   ) -> Result<Polyseed, SeedError> {
-    let features = user_features(features);
-    if !polyseed_features_supported(features) {
-      Err(SeedError::UnsupportedFeatures)?;
-    }
-
-    let birthday = birthday_encode(birthday);
-
-    if !valid_entropy(&entropy) {
-      Err(SeedError::InvalidEntropy)?;
-    }
-
-    let mut res = Polyseed { language, birthday, features, entropy, checksum: 0 };
-    res.checksum = poly_eval(&res.to_poly());
-    Ok(res)
+    from_internal(language, user_features(features), birthday_encode(birthday), entropy)
   }
 
   /// Create a new `Polyseed`.
@@ -375,9 +387,12 @@ impl Polyseed {
     let features =
       u8::try_from(extra >> DATE_BITS).expect("couldn't convert extra >> DATE_BITS to u8");
 
-    let res = Polyseed::from(lang, features, birthday_decode(birthday), entropy);
+    let res = from_internal(lang, features, birthday, entropy);
     if let Ok(res) = res.as_ref() {
-      debug_assert_eq!(res.checksum, checksum);
+      if res.checksum != checksum {
+        // This should never trigger
+        Err(SeedError::InvalidSeed)?;
+      }
     }
     res
   }