1 files changed, 70 insertions, 0 deletions
diff --git a/src/fuzzer/pow_mod.cpp b/src/fuzzer/pow_mod.cpp
new file mode 100644
index 000000000..2244c2004
--- /dev/null
+++ b/src/fuzzer/pow_mod.cpp
@@ -0,0 +1,70 @@
+/*
+* (C) 2016 Jack Lloyd
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include "fuzzers.h"
+#include <botan/numthry.h>
+#include <botan/reducer.h>
+#include <botan/pow_mod.h>
+
+namespace {
+
+Botan::BigInt simple_power_mod(Botan::BigInt x,
+                               Botan::BigInt n,
+                               const Botan::BigInt& p,
+                               const Botan::Modular_Reducer& mod_p)
+   {
+   if(n == 0)
+      {
+      if(p == 1)
+         return 0;
+      return 1;
+      }
+
+   Botan::BigInt y = 1;
+
+   while(n > 1)
+      {
+      if(n.is_odd())
+         {
+         y = mod_p.multiply(x, y);
+         }
+      x = mod_p.square(x);
+      n >>= 1;
+      }
+   return mod_p.multiply(x, y);
+   }
+
+}
+
+void fuzz(const uint8_t in[], size_t len)
+   {
+   static const size_t p_bits = 1024;
+   static const Botan::BigInt p = random_prime(fuzzer_rng(), p_bits);
+   static Botan::Modular_Reducer mod_p(p);
+
+   if(len == 0 || len > p_bits/8)
+      return;
+
+   try
+      {
+      const Botan::BigInt g = Botan::BigInt::decode(in, len / 2);
+      const Botan::BigInt x = Botan::BigInt::decode(in + len / 2, len / 2);
+
+      const Botan::BigInt ref = simple_power_mod(g, x, p, mod_p);
+      const Botan::BigInt z = Botan::power_mod(g, x, p);
+
+      if(ref != z)
+         {
+         std::cout << "G = " << g << "\n"
+                   << "X = " << x << "\n"
+                   << "P = " << p << "\n"
+                   << "Z = " << z << "\n"
+                   << "R = " << ref << "\n";
+         abort();
+         }
+      }
+   catch(Botan::Exception& e) {}
+   }