4 files changed, 51 insertions, 28 deletions

diff --git a/src/lib/utils/ct_utils.h b/src/lib/utils/ct_utils.h
index 709b6d9e5..1a88cee20 100644
--- a/src/lib/utils/ct_utils.h
+++ b/src/lib/utils/ct_utils.h
@@ -95,6 +95,12 @@ inline T expand_mask(T x)
    }
 
 template<typename T>
+inline T expand_top_bit(T a)
+   {
+   return expand_mask<T>(a >> (sizeof(T)*8-1));
+   }
+
+template<typename T>
 inline T select(T mask, T from0, T from1)
    {
    return (from0 & mask) | (from1 & ~mask);
@@ -119,19 +125,15 @@ inline T is_equal(T x, T y)
    }
 
 template<typename T>
-inline T is_less(T x, T y)
+inline T is_less(T a, T b)
    {
-   /*
-   This expands to a constant time sequence with GCC 5.2.0 on x86-64
-   but something more complicated may be needed for portable const time.
-   */
-   return expand_mask<T>(x < y);
+   return expand_top_bit(a ^ ((a^b) | ((a-b)^a)));
    }
 
 template<typename T>
-inline T is_lte(T x, T y)
+inline T is_lte(T a, T b)
    {
-   return expand_mask<T>(x <= y);
+   return CT::is_less(a, b) | CT::is_equal(a, b);
    }
 
 template<typename T>
@@ -163,26 +165,6 @@ inline void cond_zero_mem(T cond,
       }
    }
 
-template<typename T>
-inline T expand_top_bit(T a)
-   {
-   return expand_mask<T>(a >> (sizeof(T)*8-1));
-   }
-
-template<typename T>
-inline T max(T a, T b)
-   {
-   const T a_larger = b - a; // negative if a is larger
-   return select(expand_top_bit(a), a, b);
-   }
-
-template<typename T>
-inline T min(T a, T b)
-   {
-   const T a_larger = b - a; // negative if a is larger
-   return select(expand_top_bit(b), b, a);
-   }
-
 inline secure_vector<uint8_t> strip_leading_zeros(const uint8_t in[], size_t length)
    {
    size_t leading_zeros = 0;
diff --git a/src/tests/test_utils.cpp b/src/tests/test_utils.cpp
index 0ca79b6e9..d4035de65 100644
--- a/src/tests/test_utils.cpp
+++ b/src/tests/test_utils.cpp
@@ -13,6 +13,7 @@
 #include <botan/calendar.h>
 #include <botan/internal/rounding.h>
 #include <botan/internal/poly_dbl.h>
+#include <botan/internal/ct_utils.h>
 #include <botan/charset.h>
 #include <botan/parsing.h>
 
@@ -64,10 +65,44 @@ class Utility_Function_Tests : public Text_Based_Test
          std::vector<Test::Result> results;
 
          results.push_back(test_loadstore());
+         results.push_back(test_ct_utils());
 
          return results;
          }
 
+      Test::Result test_ct_utils()
+         {
+         Test::Result result("CT utils");
+
+         result.test_eq_sz("CT::is_zero8", Botan::CT::is_zero<uint8_t>(0), 0xFF);
+         result.test_eq_sz("CT::is_zero8", Botan::CT::is_zero<uint8_t>(1), 0x00);
+         result.test_eq_sz("CT::is_zero8", Botan::CT::is_zero<uint8_t>(0xFF), 0x00);
+
+         result.test_eq_sz("CT::is_zero16", Botan::CT::is_zero<uint16_t>(0), 0xFFFF);
+         result.test_eq_sz("CT::is_zero16", Botan::CT::is_zero<uint16_t>(1), 0x0000);
+         result.test_eq_sz("CT::is_zero16", Botan::CT::is_zero<uint16_t>(0xFF), 0x0000);
+
+         result.test_eq_sz("CT::is_zero32", Botan::CT::is_zero<uint32_t>(0), 0xFFFFFFFF);
+         result.test_eq_sz("CT::is_zero32", Botan::CT::is_zero<uint32_t>(1), 0x00000000);
+         result.test_eq_sz("CT::is_zero32", Botan::CT::is_zero<uint32_t>(0xFF), 0x00000000);
+
+         result.test_eq_sz("CT::is_less8", Botan::CT::is_less<uint8_t>(0, 1), 0xFF);
+         result.test_eq_sz("CT::is_less8", Botan::CT::is_less<uint8_t>(1, 0), 0x00);
+         result.test_eq_sz("CT::is_less8", Botan::CT::is_less<uint8_t>(0xFF, 5), 0x00);
+
+         result.test_eq_sz("CT::is_less16", Botan::CT::is_less<uint16_t>(0, 1), 0xFFFF);
+         result.test_eq_sz("CT::is_less16", Botan::CT::is_less<uint16_t>(1, 0), 0x0000);
+         result.test_eq_sz("CT::is_less16", Botan::CT::is_less<uint16_t>(0xFFFF, 5), 0x0000);
+
+         result.test_eq_sz("CT::is_less32", Botan::CT::is_less<uint32_t>(0, 1), 0xFFFFFFFF);
+         result.test_eq_sz("CT::is_less32", Botan::CT::is_less<uint32_t>(1, 0), 0x00000000);
+         result.test_eq_sz("CT::is_less32", Botan::CT::is_less<uint32_t>(0xFFFF5, 5), 0x00000000);
+         result.test_eq_sz("CT::is_less32", Botan::CT::is_less<uint32_t>(0xFFFFFFFF, 5), 0x00000000);
+         result.test_eq_sz("CT::is_less32", Botan::CT::is_less<uint32_t>(5, 0xFFFFFFFF), 0xFFFFFFFF);
+
+         return result;
+         }
+
       Test::Result test_loadstore()
          {
          Test::Result result("Util load/store");
diff --git a/src/tests/tests.cpp b/src/tests/tests.cpp
index 930d7c623..af2cd5909 100644
--- a/src/tests/tests.cpp
+++ b/src/tests/tests.cpp
@@ -233,6 +233,11 @@ bool Test::Result::test_eq(const std::string& what, size_t produced, size_t expe
    return test_is_eq(what, produced, expected);
    }
 
+bool Test::Result::test_eq_sz(const std::string& what, size_t produced, size_t expected)
+   {
+   return test_is_eq(what, produced, expected);
+   }
+
 bool Test::Result::test_eq(const std::string& what, OctetString produced, OctetString expected)
    {
    std::ostringstream out;
diff --git a/src/tests/tests.h b/src/tests/tests.h
index 0673705d9..16b968bd4 100644
--- a/src/tests/tests.h
+++ b/src/tests/tests.h
@@ -203,6 +203,7 @@ class Test
             bool test_eq(const std::string& what, bool produced, bool expected);
 
             bool test_eq(const std::string& what, size_t produced, size_t expected);
+            bool test_eq_sz(const std::string& what, size_t produced, size_t expected);
 
             bool test_eq(const std::string& what, OctetString produced, OctetString expected);