Merge pull request #38 from daor-oti/master-set_secure

Abstraction for architecture dependent secure memset.

Author: mczraf

lib/include/tinycrypt/utils.h

@@ -41,6 +41,7 @@
 
 #include <stdint.h>
 #include <stddef.h>
+#include <string.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -69,6 +70,31 @@ unsigned int _copy(uint8_t *to, unsigned int to_len,
  */
 void _set(void *to, uint8_t val, unsigned int len);
 
+/**
+ * @brief Set the value 'val' into the buffer 'to', 'len' times, in a way
+ *         which does not risk getting optimized out by the compiler
+ *        In cases where the compiler does not set __GNUC__ and where the
+ *         optimization level removes the memset, it may be necessary to
+ *         implement a _set_secure function and define the
+ *         TINYCRYPT_ARCH_HAS_SET_SECURE, which then can ensure that the
+ *         memset does not get optimized out.
+ *
+ * @param to OUT -- destination buffer
+ * @param val IN -- value to be set in 'to'
+ * @param len IN -- number of times the value will be copied
+ */
+#ifdef TINYCRYPT_ARCH_HAS_SET_SECURE
+extern void _set_secure(void *to, uint8_t val, unsigned int len);
+#else /* ! TINYCRYPT_ARCH_HAS_SET_SECURE */
+static inline void _set_secure(void *to, uint8_t val, unsigned int len)
+{
+  (void) memset(to, val, len);
+#ifdef __GNUC__
+  __asm__ __volatile__("" :: "g"(to) : "memory");
+#endif /* __GNUC__ */
+}
+#endif /* TINYCRYPT_ARCH_HAS_SET_SECURE */
+
 /*
  * @brief AES specific doubling function, which utilizes
  * the finite field used by AES.

lib/source/ecc_dh.c

@@ -57,6 +57,7 @@
 #include <tinycrypt/constants.h>
 #include <tinycrypt/ecc.h>
 #include <tinycrypt/ecc_dh.h>
+#include <tinycrypt/utils.h>
 #include <string.h>
 
 #if default_RNG_defined
@@ -92,7 +93,7 @@ int uECC_make_key_with_d(uint8_t *public_key, uint8_t *private_key,
 				       _public + curve->num_words);
 
 		/* erasing temporary buffer used to store secret: */
-		memset(_private, 0, NUM_ECC_BYTES);
+		_set_secure(_private, 0, NUM_ECC_BYTES);
 
 		return 1;
 	}
@@ -133,7 +134,7 @@ int uECC_make_key(uint8_t *public_key, uint8_t *private_key, uECC_Curve curve)
 					       _public + curve->num_words);
 
 			/* erasing temporary buffer that stored secret: */
-			memset(_private, 0, NUM_ECC_BYTES);
+			_set_secure(_private, 0, NUM_ECC_BYTES);
 
       			return 1;
     		}
@@ -189,12 +190,9 @@ int uECC_shared_secret(const uint8_t *public_key, const uint8_t *private_key,
 
 clear_and_out:
 	/* erasing temporary buffer used to store secret: */
-	memset(p2, 0, sizeof(p2));
-	__asm__ __volatile__("" :: "g"(p2) : "memory");
-	memset(tmp, 0, sizeof(tmp));
-	__asm__ __volatile__("" :: "g"(tmp) : "memory");
-	memset(_private, 0, sizeof(_private));
-	__asm__ __volatile__("" :: "g"(_private) : "memory");
+	_set_secure(p2, 0, sizeof(p2));
+	_set_secure(tmp, 0, sizeof(tmp));
+	_set_secure(_private, 0, sizeof(_private));
 
 	return r;
 }