Adds missing XMSS signature length check.

- Fixes out of bounds read in `XMSS_Signature` constructor when the raw
  signature data supplied as arguments is shorter than the signature size
  defined by the XMSS parameter set encoded in the `XMSS_PublicKey`.
- Fixes valid signatures with arbitrary appended data to be verified as
  correct signature.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/lib/pubkey/xmss/xmss_signature.h b/src/lib/pubkey/xmss/xmss_signature.h
index 838aae2e8..25e168fd8 100644
--- a/src/lib/pubkey/xmss/xmss_signature.h
+++ b/src/lib/pubkey/xmss/xmss_signature.h
@@ -117,7 +117,7 @@ class XMSS_Signature final
       secure_vector<uint8_t> bytes() const;
 
    private:
-      size_t m_leaf_idx;
+      uint64_t m_leaf_idx;
       secure_vector<uint8_t> m_randomness;
       XMSS_WOTS_PublicKey::TreeSignature m_tree_sig;
    };