5 files changed, 42 insertions, 6 deletions

diff --git a/src/lib/math/bigint/bigint.cpp b/src/lib/math/bigint/bigint.cpp
index fd967e66e..8874195af 100644
--- a/src/lib/math/bigint/bigint.cpp
+++ b/src/lib/math/bigint/bigint.cpp
@@ -335,6 +335,18 @@ void BigInt::shrink_to_fit(size_t min_size)
    m_reg.resize(words);
    }
 
+#if defined(BOTAN_HAS_VALGRIND)
+void BigInt::const_time_poison() const
+   {
+   CT::poison(m_reg.data(), m_reg.size());
+   }
+
+void BigInt::const_time_unpoison() const
+   {
+   CT::unpoison(m_reg.data(), m_reg.size());
+   }
+#endif
+
 void BigInt::const_time_lookup(secure_vector<word>& output,
                                const std::vector<BigInt>& vec,
                                size_t idx)
diff --git a/src/lib/math/bigint/bigint.h b/src/lib/math/bigint/bigint.h
index 44177de96..eec7f6176 100644
--- a/src/lib/math/bigint/bigint.h
+++ b/src/lib/math/bigint/bigint.h
@@ -565,6 +565,14 @@ class BOTAN_PUBLIC_API(2,0) BigInt final
      */
      void encode_words(word out[], size_t size) const;
 
+#if defined(BOTAN_HAS_VALGRIND)
+     void const_time_poison() const;
+     void const_time_unpoison() const;
+#else
+     void const_time_poison() const {}
+     void const_time_unpoison() const {}
+#endif
+
      /**
      * @param rng a random number generator
      * @param min the minimum value
diff --git a/src/lib/math/numbertheory/monty.h b/src/lib/math/numbertheory/monty.h
index 9f369f1a5..2af655230 100644
--- a/src/lib/math/numbertheory/monty.h
+++ b/src/lib/math/numbertheory/monty.h
@@ -100,6 +100,9 @@ class Montgomery_Int final
 
       Montgomery_Int& mul_by_8(secure_vector<word>& ws);
 
+      void const_time_poison() const { m_v.const_time_poison(); }
+      void const_time_unpoison() const { return m_v.const_time_unpoison(); }
+
    private:
       std::shared_ptr<const Montgomery_Params> m_params;
       BigInt m_v;
diff --git a/src/lib/math/numbertheory/monty_exp.cpp b/src/lib/math/numbertheory/monty_exp.cpp
index 4bf281fa9..b32a7ab4c 100644
--- a/src/lib/math/numbertheory/monty_exp.cpp
+++ b/src/lib/math/numbertheory/monty_exp.cpp
@@ -20,7 +20,8 @@ class Montgomery_Exponentation_State
    public:
       Montgomery_Exponentation_State(std::shared_ptr<const Montgomery_Params> params,
                                      const BigInt& g,
-                                     size_t window_bits);
+                                     size_t window_bits,
+                                     bool const_time);
 
       BigInt exponentiation(const BigInt& k) const;
 
@@ -29,13 +30,16 @@ class Montgomery_Exponentation_State
       std::shared_ptr<const Montgomery_Params> m_params;
       std::vector<Montgomery_Int> m_g;
       size_t m_window_bits;
+      bool m_const_time;
    };
 
 Montgomery_Exponentation_State::Montgomery_Exponentation_State(std::shared_ptr<const Montgomery_Params> params,
                                                                const BigInt& g,
-                                                               size_t window_bits) :
+                                                               size_t window_bits,
+                                                               bool const_time) :
    m_params(params),
-   m_window_bits(window_bits == 0 ? 4 : window_bits)
+   m_window_bits(window_bits == 0 ? 4 : window_bits),
+   m_const_time(const_time)
    {
    if(m_window_bits < 1 || m_window_bits > 12) // really even 8 is too large ...
       throw Invalid_Argument("Invalid window bits for Montgomery exponentiation");
@@ -59,6 +63,8 @@ Montgomery_Exponentation_State::Montgomery_Exponentation_State(std::shared_ptr<c
    for(size_t i = 0; i != window_size; ++i)
       {
       m_g[i].fix_size();
+      if(const_time)
+         m_g[i].const_time_poison();
       }
    }
 
@@ -91,6 +97,7 @@ void const_time_lookup(secure_vector<word>& output,
 BigInt Montgomery_Exponentation_State::exponentiation(const BigInt& scalar) const
    {
    const size_t exp_nibbles = (scalar.bits() + m_window_bits - 1) / m_window_bits;
+   CT::unpoison(exp_nibbles);
 
    Montgomery_Int x(m_params, m_params->R1(), false);
 
@@ -111,11 +118,14 @@ BigInt Montgomery_Exponentation_State::exponentiation(const BigInt& scalar) cons
       x.mul_by(e_bits, ws);
       }
 
+   x.const_time_unpoison();
    return x.value();
    }
 
 BigInt Montgomery_Exponentation_State::exponentiation_vartime(const BigInt& scalar) const
    {
+   BOTAN_ASSERT_NOMSG(m_const_time == false);
+
    const size_t exp_nibbles = (scalar.bits() + m_window_bits - 1) / m_window_bits;
 
    Montgomery_Int x(m_params, m_params->R1(), false);
@@ -135,15 +145,17 @@ BigInt Montgomery_Exponentation_State::exponentiation_vartime(const BigInt& scal
          x.mul_by(m_g[nibble], ws);
       }
 
+   x.const_time_unpoison();
    return x.value();
    }
 
 std::shared_ptr<const Montgomery_Exponentation_State>
 monty_precompute(std::shared_ptr<const Montgomery_Params> params,
                  const BigInt& g,
-                 size_t window_bits)
+                 size_t window_bits,
+                 bool const_time)
    {
-   return std::make_shared<const Montgomery_Exponentation_State>(params, g, window_bits);
+   return std::make_shared<const Montgomery_Exponentation_State>(params, g, window_bits, const_time);
    }
 
 BigInt monty_execute(const Montgomery_Exponentation_State& precomputed_state,
diff --git a/src/lib/math/numbertheory/monty_exp.h b/src/lib/math/numbertheory/monty_exp.h
index 6eeb88e7f..61da258cc 100644
--- a/src/lib/math/numbertheory/monty_exp.h
+++ b/src/lib/math/numbertheory/monty_exp.h
@@ -24,7 +24,8 @@ class Montgomery_Exponentation_State;
 std::shared_ptr<const Montgomery_Exponentation_State>
 monty_precompute(std::shared_ptr<const Montgomery_Params> params_p,
                  const BigInt& g,
-                 size_t window_bits);
+                 size_t window_bits,
+                 bool const_time = true);
 
 /*
 * Return g^x mod p