1 files changed, 15 insertions, 4 deletions
diff --git a/src/pubkey/dsa/dsa.cpp b/src/pubkey/dsa/dsa.cpp
index feac712b8..2b9a73015 100644
--- a/src/pubkey/dsa/dsa.cpp
+++ b/src/pubkey/dsa/dsa.cpp
@@ -8,6 +8,7 @@
 #include <botan/dsa.h>
 #include <botan/numthry.h>
 #include <botan/keypair.h>
+#include <future>
 
 namespace Botan {
 
@@ -95,10 +96,14 @@ DSA_Signature_Operation::sign(const byte msg[], u32bit msg_len,
       k.randomize(rng, q.bits());
    while(k >= q);
 
+   auto future_r = std::async(std::launch::async,
+                              [&]() { return mod_q.reduce(powermod_g_p(k)); });
+
    BigInt i(msg, msg_len);
 
-   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("DSA signature gen failure: r or s was zero");
@@ -134,8 +139,14 @@ bool DSA_Verification_Operation::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);
    }