Add multiexponentation interface to DL_Group

2 files changed, 17 insertions, 3 deletions

diff --git a/src/lib/pubkey/dl_group/dl_group.cpp b/src/lib/pubkey/dl_group/dl_group.cpp
index ff8ba3727..9bd9d2462 100644
--- a/src/lib/pubkey/dl_group/dl_group.cpp
+++ b/src/lib/pubkey/dl_group/dl_group.cpp
@@ -45,6 +45,9 @@ class DL_Group_Data final
          return m_mod_p.multiply(x, y);
          }
 
+      std::shared_ptr<const Montgomery_Params> monty_params() const
+         { return m_monty_params; }
+
       size_t p_bits() const { return m_p_bits; }
       size_t p_bytes() const { return (m_p_bits + 7) / 8; }
 
@@ -422,6 +425,11 @@ BigInt DL_Group::multiply_mod_p(const BigInt& x, const BigInt& y) const
    return data().multiply_mod_p(x, y);
    }
 
+BigInt DL_Group::multi_exponentiate(const BigInt& x, const BigInt& y, const BigInt& z) const
+   {
+   return monty_multi_exp(data().monty_params(), get_g(), x, y, z);
+   }
+
 BigInt DL_Group::power_g_p(const BigInt& x) const
    {
    return data().power_g_p(x);
diff --git a/src/lib/pubkey/dl_group/dl_group.h b/src/lib/pubkey/dl_group/dl_group.h
index a3dcfbdf0..14ef3c088 100644
--- a/src/lib/pubkey/dl_group/dl_group.h
+++ b/src/lib/pubkey/dl_group/dl_group.h
@@ -166,13 +166,13 @@ class BOTAN_PUBLIC_API(2,0) DL_Group final
       */
       std::vector<uint8_t> DER_encode(Format format) const;
 
-      /*
+      /**
       * Reduce an integer modulo p
       * @return x % p
       */
       BigInt mod_p(const BigInt& x) const;
 
-      /*
+      /**
       * Multiply and reduce an integer modulo p
       * @return (x*y) % p
       */
@@ -180,13 +180,19 @@ class BOTAN_PUBLIC_API(2,0) DL_Group final
 
       BigInt inverse_mod_p(const BigInt& x) const;
 
-      /*
+      /**
       * Modular exponentiation
       * @return (g^x) % p
       */
       BigInt power_g_p(const BigInt& x) const;
 
       /**
+      * Multi-exponentiate
+      * Return (g^x * y^z) % p
+      */
+      BigInt multi_exponentiate(const BigInt& x, const BigInt& y, const BigInt& z) const;
+
+      /**
       * Return the size of p in bits
       * Same as get_p().bits()
       */