1 files changed, 17 insertions, 5 deletions
diff --git a/src/pubkey/dsa/dsa_op.cpp b/src/pubkey/dsa/dsa_op.cpp
index 5b921441d..e83fd83b7 100644
--- a/src/pubkey/dsa/dsa_op.cpp
+++ b/src/pubkey/dsa/dsa_op.cpp
@@ -1,11 +1,12 @@
 /*
 * DSA Operations
-* (C) 1999-2007 Jack Lloyd
+* (C) 1999-2009 Jack Lloyd
 *
 * Distributed under the terms of the Botan license
 */
 
 #include <botan/dsa_op.h>
+#include <future>
 
 namespace Botan {
 
@@ -40,8 +41,14 @@ bool Default_DSA_Op::verify(const byte msg[], u32bit msg_len,
       return false;
 
    s = inverse_mod(s, q);
-   s = mod_p.multiply(powermod_g_p(mod_q.multiply(s, i)),
-                      powermod_y_p(mod_q.multiply(s, r)));
+
+   auto future_s_i = std::async(std::launch::async,
+      [&]() { return powermod_g_p(mod_q.multiply(s, i)); });
+
+   BigInt s_r = powermod_y_p(mod_q.multiply(s, r));
+   BigInt s_i = future_s_i.get();
+
+   s = mod_p.multiply(s_i, s_r);
 
    return (mod_q.reduce(s) == r);
    }
@@ -55,11 +62,16 @@ SecureVector<byte> Default_DSA_Op::sign(const byte in[], u32bit length,
    if(x == 0)
       throw Internal_Error("Default_DSA_Op::sign: No private key");
 
+   auto future_r = std::async(std::launch::async,
+                              [&]() { return mod_q.reduce(powermod_g_p(k)); });
+
    const BigInt& q = group.get_q();
    BigInt i(in, length);
 
-   BigInt r = mod_q.reduce(powermod_g_p(k));
-   BigInt s = mod_q.multiply(inverse_mod(k, q), mul_add(x, r, i));
+   BigInt s = inverse_mod(k, q);
+   BigInt r = future_r.get();
+
+   s = mod_q.multiply(s, mul_add(x, r, i));
 
    if(r.is_zero() || s.is_zero())
       throw Internal_Error("Default_DSA_Op::sign: r or s was zero");