Add missing q == 0 check in DL_Scheme_PublicKey::check_key() as q may not be available in all groups

1 files changed, 19 insertions, 7 deletions

diff --git a/src/lib/pubkey/dl_algo/dl_algo.cpp b/src/lib/pubkey/dl_algo/dl_algo.cpp
index 472b979b1..85576e9bf 100644
--- a/src/lib/pubkey/dl_algo/dl_algo.cpp
+++ b/src/lib/pubkey/dl_algo/dl_algo.cpp
@@ -35,8 +35,8 @@ std::vector<byte> DL_Scheme_PublicKey::public_key_bits() const
    }
 
 DL_Scheme_PublicKey::DL_Scheme_PublicKey(const AlgorithmIdentifier& alg_id,
-                                         const std::vector<byte>& key_bits,
-                                         DL_Group::Format format)
+      const std::vector<byte>& key_bits,
+      DL_Group::Format format)
    {
    m_group.BER_decode(alg_id.parameters, format);
 
@@ -49,8 +49,8 @@ secure_vector<byte> DL_Scheme_PrivateKey::private_key_bits() const
    }
 
 DL_Scheme_PrivateKey::DL_Scheme_PrivateKey(const AlgorithmIdentifier& alg_id,
-                                           const secure_vector<byte>& key_bits,
-                                           DL_Group::Format format)
+      const secure_vector<byte>& key_bits,
+      DL_Group::Format format)
    {
    m_group.BER_decode(alg_id.parameters, format);
 
@@ -63,12 +63,24 @@ DL_Scheme_PrivateKey::DL_Scheme_PrivateKey(const AlgorithmIdentifier& alg_id,
 bool DL_Scheme_PublicKey::check_key(RandomNumberGenerator& rng,
                                     bool strong) const
    {
-   if(m_y < 2 || m_y >= group_p())
+   const BigInt& p = group_p();
+
+   if(m_y < 2 || m_y >= p)
       return false;
    if(!m_group.verify_group(rng, strong))
       return false;
-   if(power_mod(m_y,group_q(),group_p()) != 1)
-      return false;
+
+   try
+      {
+      const BigInt& q = group_q();
+      if(power_mod(m_y, q, p) != 1)
+         return false;
+      }
+   catch(const Invalid_State& e)
+      {
+      return true;
+      }
+
    return true;
    }