/*
- * Copyright 2014-2016 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 2014-2018 The OpenSSL Project Authors. All Rights Reserved.
*
- * Licensed under the OpenSSL license (the "License"). You may not use
+ * Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
# define HEADER_CONSTANT_TIME_LOCL_H
# include <stdlib.h>
+# include <string.h>
# include <openssl/e_os2.h> /* For 'ossl_inline' */
-#ifdef __cplusplus
-extern "C" {
-#endif
-
/*-
* 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);
*/
-/*
- * Returns the given value with the MSB copied to all the other
- * bits. Uses the fact that arithmetic shift shifts-in the sign bit.
- * However, this is not ensured by the C standard so you may need to
- * replace this with something else on odd CPUs.
- */
+/* 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);
-/*
- * 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);
+/* 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.
- */
+/* 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. */
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);
/* 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 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);
+}
+
static ossl_inline size_t constant_time_msb_s(size_t a)
{
return 0 - (a >> (sizeof(a) * 8 - 1));
static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
unsigned int b)
{
- return (unsigned char)(constant_time_lt(a, b));
+ 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,
static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
unsigned int b)
{
- return (unsigned char)(constant_time_ge(a, b));
+ return (unsigned char)constant_time_ge(a, b);
}
static ossl_inline unsigned char constant_time_ge_8_s(size_t a, size_t b)
{
- return (unsigned char)(constant_time_ge_s(a, b));
+ return (unsigned char)constant_time_ge_s(a, b);
}
static ossl_inline unsigned int constant_time_is_zero(unsigned int a)
static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a)
{
- return (unsigned char)(constant_time_is_zero(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,
static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
unsigned int b)
{
- return (unsigned char)(constant_time_eq(a, b));
+ return (unsigned char)constant_time_eq(a, b);
}
static ossl_inline unsigned char constant_time_eq_8_s(size_t a, size_t b)
{
- return (unsigned char)(constant_time_eq_s(a, b));
+ return (unsigned char)constant_time_eq_s(a, b);
}
static ossl_inline unsigned int constant_time_eq_int(int a, int b)
return constant_time_eq_8((unsigned)(a), (unsigned)(b));
}
+/*
+ * Returns the value unmodified, but avoids optimizations.
+ * The barriers prevent the compiler from narrowing down the
+ * possible value range of the mask and ~mask in the select
+ * statements, which avoids the recognition of the select
+ * and turning it into a conditional load or branch.
+ */
+static ossl_inline unsigned int value_barrier(unsigned int a)
+{
+#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
+ unsigned int r;
+ __asm__("" : "=r"(r) : "0"(a));
+#else
+ volatile unsigned int r = a;
+#endif
+ return r;
+}
+
+/* Convenience method for uint32_t. */
+static ossl_inline uint32_t value_barrier_32(uint32_t a)
+{
+#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
+ uint32_t r;
+ __asm__("" : "=r"(r) : "0"(a));
+#else
+ volatile uint32_t r = a;
+#endif
+ return r;
+}
+
+/* Convenience method for uint64_t. */
+static ossl_inline uint64_t value_barrier_64(uint64_t a)
+{
+#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
+ uint64_t r;
+ __asm__("" : "=r"(r) : "0"(a));
+#else
+ volatile uint64_t r = a;
+#endif
+ return r;
+}
+
+/* Convenience method for size_t. */
+static ossl_inline size_t value_barrier_s(size_t a)
+{
+#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
+ size_t r;
+ __asm__("" : "=r"(r) : "0"(a));
+#else
+ volatile size_t r = a;
+#endif
+ return r;
+}
+
static ossl_inline unsigned int constant_time_select(unsigned int mask,
unsigned int a,
unsigned int b)
{
- return (mask & a) | (~mask & b);
+ return (value_barrier(mask) & a) | (value_barrier(~mask) & b);
}
static ossl_inline size_t constant_time_select_s(size_t mask,
size_t a,
size_t b)
{
- return (mask & a) | (~mask & b);
+ return (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b);
}
static ossl_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));
+ return (unsigned char)constant_time_select(mask, a, b);
}
static ossl_inline int constant_time_select_int(unsigned int mask, int a,
int b)
{
- return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b)));
+ return (int)constant_time_select(mask, (unsigned)(a), (unsigned)(b));
}
static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
{
- return (int)(constant_time_select((unsigned)mask, (unsigned)(a),
- (unsigned)(b)));
+ return (int)constant_time_select((unsigned)mask, (unsigned)(a),
+ (unsigned)(b));
+}
+
+static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
+ uint32_t b)
+{
+ return (value_barrier_32(mask) & a) | (value_barrier_32(~mask) & b);
}
-#ifdef __cplusplus
+static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
+ uint64_t b)
+{
+ return (value_barrier_64(mask) & a) | (value_barrier_64(~mask) & b);
}
-#endif
+
+/*
+ * 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);
+ }
+}
+
+/*
+ * Expected usage pattern is to unconditionally set error and then
+ * wipe it if there was no actual error. |clear| is 1 or 0.
+ */
+void err_clear_last_constant_time(int clear);
#endif /* HEADER_CONSTANT_TIME_LOCL_H */
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