Add constant-time 64

Standardize comments.
Reviewed-by: NAndy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3727)

include/internal/constant_time_locl.h

@@ -21,17 +21,14 @@ extern "C" {
  * The boolean methods return a bitmask of all ones (0xff...f) for true
  * and 0 for false. This is useful for choosing a value based on the result
  * of a conditional in constant time. For example,
- *
- * if (a < b) {
- *   c = a;
- * } else {
- *   c = b;
- * }
- *
+ *      if (a < b) {
+ *        c = a;
+ *      } else {
+ *        c = b;
+ *      }
  * can be written as
- *
- * unsigned int lt = constant_time_lt(a, b);
- * c = constant_time_select(lt, a, b);
+ *      unsigned int lt = constant_time_lt(a, b);
+ *      c = constant_time_select(lt, a, b);
  */
 
 /*
@@ -41,35 +38,31 @@ extern "C" {
  * replace this with something else on odd CPUs.
  */
 static ossl_inline unsigned int constant_time_msb(unsigned int a);
+/* Convenience method for uint64_t. */
+static ossl_inline uint64_t constant_time_msb_64(uint64_t a);
 
-/*
- * Returns 0xff..f if a < b and 0 otherwise.
- */
+/* Returns 0xff..f if a < b and 0 otherwise. */
 static ossl_inline unsigned int constant_time_lt(unsigned int a,
                                                  unsigned int b);
 /* Convenience method for getting an 8-bit mask. */
 static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
                                                     unsigned int b);
+/* Convenience method for uint64_t. */
+static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b);
 
-/*
- * Returns 0xff..f if a >= b and 0 otherwise.
- */
+/* Returns 0xff..f if a >= b and 0 otherwise. */
 static ossl_inline unsigned int constant_time_ge(unsigned int a,
                                                  unsigned int b);
 /* Convenience method for getting an 8-bit mask. */
 static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
                                                     unsigned int b);
 
-/*
- * Returns 0xff..f if a == 0 and 0 otherwise.
- */
+/* Returns 0xff..f if a == 0 and 0 otherwise. */
 static ossl_inline unsigned int constant_time_is_zero(unsigned int a);
 /* Convenience method for getting an 8-bit mask. */
 static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a);
 
-/*
- * Returns 0xff..f if a == b and 0 otherwise.
- */
+/* Returns 0xff..f if a == b and 0 otherwise. */
 static ossl_inline unsigned int constant_time_eq(unsigned int a,
                                                  unsigned int b);
 /* Convenience method for getting an 8-bit mask. */
@@ -94,15 +87,24 @@ static ossl_inline unsigned int constant_time_select(unsigned int mask,
 static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
                                                         unsigned char a,
                                                         unsigned char b);
+/* Convenience method for uint64_t. */
+static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
+                                                    uint64_t b);
 /* Convenience method for signed integers. */
 static ossl_inline int constant_time_select_int(unsigned int mask, int a,
                                                 int b);
 
+
 static ossl_inline unsigned int constant_time_msb(unsigned int a)
 {
     return 0 - (a >> (sizeof(a) * 8 - 1));
 }
 
+static ossl_inline uint64_t constant_time_msb_64(uint64_t a)
+{
+    return 0 - (a >> 63);
+}
+
 static ossl_inline size_t constant_time_msb_s(size_t a)
 {
     return 0 - (a >> (sizeof(a) * 8 - 1));
@@ -125,6 +127,11 @@ static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
     return (unsigned char)(constant_time_lt(a, b));
 }
 
+static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b)
+{
+    return constant_time_msb_64(a ^ ((a ^ b) | ((a - b) ^ b)));
+}
+
 static ossl_inline unsigned int constant_time_ge(unsigned int a,
                                                  unsigned int b)
 {
@@ -227,6 +234,12 @@ static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
                                       (unsigned)(b)));
 }
 
+static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
+                                                    uint64_t b)
+{
+    return (mask & a) | (~mask & b);
+}
+
 #ifdef __cplusplus
 }
 #endif

test/constant_time_test.c

@@ -21,6 +21,8 @@ static const unsigned char CONSTTIME_TRUE_8 = 0xff;
 static const unsigned char CONSTTIME_FALSE_8 = 0;
 static const size_t CONSTTIME_TRUE_S = ~((size_t)0);
 static const size_t CONSTTIME_FALSE_S = 0;
+static uint64_t CONSTTIME_TRUE_64 = (uint64_t)(~(uint64_t)0);
+static uint64_t CONSTTIME_FALSE_64 = 0;
 
 static int test_binary_op(unsigned int (*op) (unsigned int a, unsigned int b),
                           const char *op_name, unsigned int a, unsigned int b,
@@ -56,6 +58,25 @@ static int test_binary_op_s(size_t (*op) (size_t a, size_t b),
     return 1;
 }
 
+static int test_binary_op_64(uint64_t (*op)(uint64_t a, uint64_t b),
+                             const char *op_name, uint64_t a, uint64_t b,
+                             int is_true)
+{
+    uint64_t c = op(a, b);
+
+    if (is_true && c != CONSTTIME_TRUE_64) {
+        TEST_error("TRUE %s op failed", op_name);
+        BIO_printf(bio_err, "a=%jx b=%jx\n", a, b);
+        return 0;
+    } else if (!is_true && c != CONSTTIME_FALSE_64) {
+        TEST_error("FALSE %s op failed", op_name);
+        BIO_printf(bio_err, "a=%jx b=%jx\n", a, b);
+        return 0;
+    }
+    return 1;
+}
+
+
 static int test_is_zero(unsigned int a)
 {
     if (a == 0 && !TEST_uint_eq(constant_time_is_zero(a), CONSTTIME_TRUE))
@@ -110,6 +131,23 @@ static int test_select_s(unsigned char a, unsigned char b)
     return 1;
 }
 
+static int test_select_64(uint64_t a, uint64_t b)
+{
+    uint64_t selected = constant_time_select_64(CONSTTIME_TRUE_64, a, b);
+
+    if (selected != a) {
+        TEST_error("test_select_64 TRUE failed");
+        BIO_printf(bio_err, "a=%jx b=%jx got %jx wanted a\n", a, b, selected);
+        return 0;
+    }
+    selected = constant_time_select_64(CONSTTIME_FALSE_64, a, b);
+    if (selected != b) {
+        BIO_printf(bio_err, "a=%jx b=%jx got %jx wanted b\n", a, b, selected);
+        return 0;
+    }
+    return 1;
+}
+
 static int test_select_int(int a, int b)
 {
     if (!TEST_int_eq(constant_time_select_int(CONSTTIME_TRUE, a, b), a))
@@ -146,26 +184,33 @@ static int test_eq_int(int a, int b)
     return 1;
 }
 
-static unsigned int test_values[] =
-    { 0, 1, 1024, 12345, 32000, UINT_MAX / 2 - 1,
+static unsigned int test_values[] = {
+    0, 1, 1024, 12345, 32000, UINT_MAX / 2 - 1,
     UINT_MAX / 2, UINT_MAX / 2 + 1, UINT_MAX - 1,
     UINT_MAX
 };
 
-static unsigned char test_values_8[] =
-    { 0, 1, 2, 20, 32, 127, 128, 129, 255 };
+static unsigned char test_values_8[] = {
+    0, 1, 2, 20, 32, 127, 128, 129, 255
+};
 
-static int signed_test_values[] = { 0, 1, -1, 1024, -1024, 12345, -12345,
+static int signed_test_values[] = {
+    0, 1, -1, 1024, -1024, 12345, -12345,
     32000, -32000, INT_MAX, INT_MIN, INT_MAX - 1,
     INT_MIN + 1
 };
 
-static size_t test_values_s[] =
-    { 0, 1, 1024, 12345, 32000, SIZE_MAX / 2 - 1,
+static size_t test_values_s[] = {
+    0, 1, 1024, 12345, 32000, SIZE_MAX / 2 - 1,
     SIZE_MAX / 2, SIZE_MAX / 2 + 1, SIZE_MAX - 1,
     SIZE_MAX
 };
 
+static uint64_t test_values_64[] = {
+    0, 1, 1024, 12345, 32000, 32000000, 32000000001, UINT64_MAX / 2,
+    UINT64_MAX / 2 + 1, UINT64_MAX - 1, UINT64_MAX
+};
+
 static int test_sizeofs(void)
 {
     if (!TEST_uint_eq(OSSL_NELEM(test_values), OSSL_NELEM(test_values_s)))
@@ -264,6 +309,23 @@ static int test_8values(int i)
     return ret;
 }
 
+static int test_64values(int i)
+{
+    uint64_t g = test_values_64[i];
+    int j, ret = 1;
+
+    for (j = i + 1; j < (int)OSSL_NELEM(test_values_64); j++) {
+        uint64_t h = test_values_64[j];
+
+        if (!test_binary_op_64(&constant_time_lt_64, "constant_time_lt_64",
+                               g, h, g < h)
+                || !test_select_64(g, h)) {
+            TEST_info("test_64values failed i=%d j=%d", i, j);
+            ret = 0;
+        }
+    }
+    return ret;
+}
 
 void register_tests(void)
 {
@@ -271,4 +333,5 @@ void register_tests(void)
     ADD_ALL_TESTS(test_binops, OSSL_NELEM(test_values));
     ADD_ALL_TESTS(test_signed, OSSL_NELEM(signed_test_values));
     ADD_ALL_TESTS(test_8values, sizeof(test_values_8));
+    ADD_ALL_TESTS(test_64values, sizeof(test_values_64));
 }