The gf2m type is an unsigned 16-bit, so under C promotion rules a

shift promotes to signed int rather than an unsigned value. However
here we wish to use a large shift, which can cause a signed overflow.
Add static_cast to force to the desired (unsigned) type.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/lib/pubkey/mce/code_based_key_gen.cpp b/src/lib/pubkey/mce/code_based_key_gen.cpp
index 7adf85112..a3749abef 100644
--- a/src/lib/pubkey/mce/code_based_key_gen.cpp
+++ b/src/lib/pubkey/mce/code_based_key_gen.cpp
@@ -156,7 +156,7 @@ McEliece_PrivateKey generate_mceliece_key( RandomNumberGenerator & rng, u32bit e
          {
          k = (l * ext_deg) / 32;
          j = (l * ext_deg) % 32;
-         sk[k] ^= F[i].get_coef( l) << j;
+         sk[k] ^= static_cast<u32bit>(F[i].get_coef(l)) << j;
          if (j + ext_deg > 32)
             {
             sk[k + 1] ^= F[i].get_coef( l) >> (32 - j);