fix(core): zeroize keyfile decode intermediate + clearer errors + error-arm tests

crates/relicario-core/src/keyfile.rs

@@ -40,15 +40,21 @@ pub fn keyfile_decode(bytes: &[u8]) -> Result<Zeroizing<[u8; 32]>> {
     if lines.next() != Some(HEADER) {
         return Err(RelicarioError::Format("bad key-file header".into()));
     }
-    let b64 = lines.next().unwrap_or("").trim();
-    let decoded = STANDARD
-        .decode(b64)
-        .map_err(|_| RelicarioError::Format("key-file body not base64".into()))?;
-    let arr: [u8; 32] = decoded
-        .as_slice()
-        .try_into()
-        .map_err(|_| RelicarioError::Format("key-file secret must be 32 bytes".into()))?;
-    Ok(Zeroizing::new(arr))
+    let b64 = match lines.next() {
+        Some(line) => line.trim(),
+        None => return Err(RelicarioError::Format("key-file missing body line".into())),
+    };
+    let decoded: Zeroizing<Vec<u8>> = Zeroizing::new(
+        STANDARD
+            .decode(b64)
+            .map_err(|_| RelicarioError::Format("key-file body not base64".into()))?,
+    );
+    if decoded.len() != 32 {
+        return Err(RelicarioError::Format("key-file secret must be 32 bytes".into()));
+    }
+    let mut arr = Zeroizing::new([0u8; 32]);
+    arr.copy_from_slice(&decoded);
+    Ok(arr)
 }
 
 #[cfg(test)]
@@ -70,4 +76,12 @@ mod tests {
     fn rejects_wrong_length() {
         assert!(keyfile_decode(b"relicario-keyfile-v1\nAAAA\n").is_err()); // decodes to <32 bytes
     }
+    #[test]
+    fn rejects_non_utf8() {
+        assert!(keyfile_decode(b"\xff\xfe\nAAAA\n").is_err());
+    }
+    #[test]
+    fn rejects_missing_body() {
+        assert!(keyfile_decode(b"relicario-keyfile-v1\n").is_err());
+    }
 }