From e0fa632420adaab5f0c5fb1db7190dcbd7637a18 Mon Sep 17 00:00:00 2001
From: Matt Caswell <matt@openssl.org>
Date: Thu, 1 Feb 2018 13:51:53 +0000
Subject: [PATCH] Add some new constant time functions needed by curve448

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/5105)
---
 include/internal/constant_time_locl.h | 93 +++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)

diff --git a/include/internal/constant_time_locl.h b/include/internal/constant_time_locl.h
index c60e59c6a5..813df63698 100644
--- a/include/internal/constant_time_locl.h
+++ b/include/internal/constant_time_locl.h
@@ -11,6 +11,7 @@
 # define HEADER_CONSTANT_TIME_LOCL_H
 
 # include <stdlib.h>
+# include <string.h>
 # include <openssl/e_os2.h>              /* For 'ossl_inline' */
 
 #ifdef __cplusplus
@@ -33,6 +34,8 @@ extern "C" {
 
 /* Returns the given value with the MSB copied to all the other bits. */
 static ossl_inline unsigned int constant_time_msb(unsigned int a);
+/* Convenience method for uint32_t. */
+static ossl_inline uint32_t constant_time_msb_32(uint32_t a);
 /* Convenience method for uint64_t. */
 static ossl_inline uint64_t constant_time_msb_64(uint64_t a);
 
@@ -56,6 +59,8 @@ static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
 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);
+/* Convenience method for getting a 32-bit mask. */
+static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a);
 
 /* Returns 0xff..f if a == b and 0 otherwise. */
 static ossl_inline unsigned int constant_time_eq(unsigned int a,
@@ -82,6 +87,11 @@ 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 uint32_t. */
+static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
+                                                    uint32_t b);
+
 /* Convenience method for uint64_t. */
 static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
                                                     uint64_t b);
@@ -95,6 +105,12 @@ static ossl_inline unsigned int constant_time_msb(unsigned int a)
     return 0 - (a >> (sizeof(a) * 8 - 1));
 }
 
+
+static ossl_inline uint32_t constant_time_msb_32(uint32_t a)
+{
+    return 0 - (a >> 31);
+}
+
 static ossl_inline uint64_t constant_time_msb_64(uint64_t a)
 {
     return 0 - (a >> 63);
@@ -164,6 +180,11 @@ static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a)
     return (unsigned char)constant_time_is_zero(a);
 }
 
+static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a)
+{
+    return constant_time_msb_32(~a & (a - 1));
+}
+
 static ossl_inline unsigned int constant_time_eq(unsigned int a,
                                                  unsigned int b)
 {
@@ -229,12 +250,84 @@ static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
                                       (unsigned)(b));
 }
 
+static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
+                                                    uint32_t b)
+{
+    return (mask & a) | (~mask & b);
+}
+
 static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
                                                     uint64_t b)
 {
     return (mask & a) | (~mask & b);
 }
 
+/*
+ * mask must be 0xFFFFFFFF or 0x00000000.
+ *
+ * if (mask) {
+ *     uint32_t tmp = *a;
+ *
+ *     *a = *b;
+ *     *b = tmp;
+ * }
+ */
+static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a,
+                                                   uint32_t *b)
+{
+    uint32_t xor = *a ^ *b;
+
+    xor &= mask;
+    *a ^= xor;
+    *b ^= xor;
+}
+
+/*
+ * mask must be 0xFFFFFFFF or 0x00000000.
+ *
+ * if (mask) {
+ *     uint64_t tmp = *a;
+ *
+ *     *a = *b;
+ *     *b = tmp;
+ * }
+ */
+static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a,
+                                                   uint64_t *b)
+{
+    uint64_t xor = *a ^ *b;
+
+    xor &= mask;
+    *a ^= xor;
+    *b ^= xor;
+}
+
+/*
+ * table is a two dimensional array of bytes. Each row has rowsize elements.
+ * Copies row number idx into out. rowsize and numrows are not considered
+ * private.
+ */
+static ossl_inline void constant_time_lookup(void *out,
+                                             const void *table,
+                                             size_t rowsize,
+                                             size_t numrows,
+                                             size_t idx)
+{
+    size_t i, j;
+    const unsigned char *tablec = (const unsigned char *)table;
+    unsigned char *outc = (unsigned char *)out;
+    unsigned char mask;
+
+    memset(out, 0, rowsize);
+
+    /* Note idx may underflow - but that is well defined */
+    for (i = 0; i < numrows; i++, idx--) {
+        mask = (unsigned char)constant_time_is_zero_s(idx);
+        for (j = 0; j < rowsize; j++)
+            *(outc + j) |= constant_time_select_8(mask, *(tablec++), 0);
+    }
+}
+
 #ifdef __cplusplus
 }
 #endif
-- 
2.25.1