X-Git-Url: https://git.openssl.org/?p=openssl.git;a=blobdiff_plain;f=crypto%2Fconstant_time_locl.h;h=6410ca789b07494c1aa3172be4e5e4cd7f7fc1a4;hp=0d3acd58b3a4da97a8ac83b5224209d6ac4aa6ea;hb=1566497495b30054453b05d275c01d6db5211e2a;hpb=e517dfd3d1a1e4dcb37689274aead3daaedc98af

diff --git a/crypto/constant_time_locl.h b/crypto/constant_time_locl.h
index 0d3acd58b3..6410ca789b 100644
--- a/crypto/constant_time_locl.h
+++ b/crypto/constant_time_locl.h
@@ -1,5 +1,5 @@
 /* crypto/constant_time_locl.h */
-/*
+/*-
  * Utilities for constant-time cryptography.
  *
  * Author: Emilia Kasper (emilia@openssl.org)
@@ -53,8 +53,8 @@
 extern "C" {
 #endif
 
-/*
- * The following methods return a bitmask of all ones (0xff...f) for true
+/*-
+ * 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,
  *
@@ -67,7 +67,7 @@ extern "C" {
  * can be written as
  *
  * unsigned int lt = constant_time_lt(a, b);
- * c = a & lt | b & ~lt;
+ * c = constant_time_select(lt, a, b);
  */
 
 /*
@@ -106,20 +106,35 @@ static inline unsigned char constant_time_is_zero_8(unsigned int a);
 static inline unsigned int constant_time_eq(unsigned int a, unsigned int b);
 /* Convenience method for getting an 8-bit mask. */
 static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b);
+/* Signed integers. */
+static inline unsigned int constant_time_eq_int(int a, int b);
+/* Convenience method for getting an 8-bit mask. */
+static inline unsigned char constant_time_eq_int_8(int a, int b);
+
+
+/*-
+ * Returns (mask & a) | (~mask & b).
+ *
+ * When |mask| is all 1s or all 0s (as returned by the methods above),
+ * the select methods return either |a| (if |mask| is nonzero) or |b|
+ * (if |mask| is zero).
+ */
+static inline unsigned int constant_time_select(unsigned int mask,
+	unsigned int a, unsigned int b);
+/* Convenience method for unsigned chars. */
+static inline unsigned char constant_time_select_8(unsigned char mask,
+	unsigned char a, unsigned char b);
+/* Convenience method for signed integers. */
+static inline int constant_time_select_int(unsigned int mask, int a, int b);
 
 static inline unsigned int constant_time_msb(unsigned int a)
 	{
-	return (unsigned int)((int)(a) >> (sizeof(int) * 8 - 1));
+	return 0-(a >> (sizeof(a) * 8 - 1));
 	}
 
 static inline unsigned int constant_time_lt(unsigned int a, unsigned int b)
 	{
-	unsigned int lt;
-	/* Case 1: msb(a) == msb(b). a < b iff the MSB of a - b is set.*/
-	lt = ~(a ^ b) & (a - b);
-	/* Case 2: msb(a) != msb(b). a < b iff the MSB of b is set. */
-	lt |= ~a & b;
-	return constant_time_msb(lt);
+	return constant_time_msb(a^((a^b)|((a-b)^b)));
 	}
 
 static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b)
@@ -129,12 +144,7 @@ static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b)
 
 static inline unsigned int constant_time_ge(unsigned int a, unsigned int b)
 	{
-	unsigned int ge;
-	/* Case 1: msb(a) == msb(b). a >= b iff the MSB of a - b is not set.*/
-	ge = ~((a ^ b) | (a - b));
-	/* Case 2: msb(a) != msb(b). a >= b iff the MSB of a is set. */
-	ge |= a & ~b;
-	return constant_time_msb(ge);
+	return ~constant_time_lt(a, b);
 	}
 
 static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b)
@@ -162,6 +172,33 @@ static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b)
 	return (unsigned char)(constant_time_eq(a, b));
 	}
 
+static inline unsigned int constant_time_eq_int(int a, int b)
+	{
+	return constant_time_eq((unsigned)(a), (unsigned)(b));
+	}
+
+static inline unsigned char constant_time_eq_int_8(int a, int b)
+	{
+	return constant_time_eq_8((unsigned)(a), (unsigned)(b));
+	}
+
+static inline unsigned int constant_time_select(unsigned int mask,
+	unsigned int a, unsigned int b)
+	{
+	return (mask & a) | (~mask & b);
+	}
+
+static inline unsigned char constant_time_select_8(unsigned char mask,
+	unsigned char a, unsigned char b)
+	{
+	return (unsigned char)(constant_time_select(mask, a, b));
+	}
+
+static inline int constant_time_select_int(unsigned int mask, int a, int b)
+	{
+	return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b)));
+	}
+
 #ifdef __cplusplus
 }
 #endif