Added ksecprintf for securely printing messages from the kernel.

If SECRET_TESTING is defined, the function will compute and print
a salt value and the hmac/sha256 hash of the message, which can be
verified from the test161 server.

kern/include/kern/secret.h

@@ -45,6 +45,6 @@
  */
 
 #undef SECRET_TESTING
-#define SECRET 0
+#define SECRET ""
 
 #endif /* _SECRET_H_ */

kern/include/test.h

@@ -174,7 +174,9 @@ int ll16test(int, char **);
 #define SUCCESS 0
 #define FAIL 1
 
-void success(bool, uint32_t, const char *);
+int success(bool, const char *, const char *);
+
+int ksecprintf(const char *secret, const char *msg, const char *name);
 
 void random_yielder(uint32_t);
 void random_spinner(uint32_t);

kern/test/lib.c

@@ -3,55 +3,54 @@
 #include <thread.h>
 #include <test.h>
 #include <lib.h>
+#include <kern/secure.h>
 
 /*
- * Main success function for kernel tests. Prints a multiple of the secret if
- * the secret is non-zero and the test succeeded. Otherwise prints a random
- * number.
- *
- * Ideally we would multiply the secret (a large prime) by another large prime
- * to ensure that factoring was hard, but that would require either primality
- * testing (slow) or augmenting sys161 with a prime number generator. This is
- * sufficient for now to prevent replay attacks.
+ * Common success function for kernel tests. If SECRET_TESTING is defined,
+ * ksecprintf will compute the hmac/sha256 hash of any message using the
+ * shared secret and a random salt value. The (secure) server also knows
+ * the secret and can verify the message was generated by a trusted source.
+ * The salt value prevents against replay attacks.
  */
-
-#define MIN_MULTIPLIER 0x80000000
+int
+success(bool status, const char * secret, const char * name) {
+	if (status == SUCCESS) {
+		return ksecprintf(secret, "SUCCESS", name);
+	} else {
+		return ksecprintf(secret, "FAIL", name);
+	}
+}
 
 #ifndef SECRET_TESTING
-void
-success(bool status, uint32_t secret, const char * name) {
+
+int
+ksecprintf(const char * secret, const char * msg, const char * name)
+{
 	(void)secret;
-	if (status == SUCCESS) {
-		kprintf("%s: SUCCESS\n", name);
-	} else {	
-		kprintf("%s: FAIL\n", name);
-	}
-	return;
+	return kprintf("%s: %s\n", name, msg);
 }
+
 #else
-void
-success(bool status, uint32_t secret, const char * name) {
-	uint32_t multiplier;
-	// Make sure we can get large random numbers
-	KASSERT(randmax() == 0xffffffff);
-	while (1) {
-		multiplier = random();
-		// We can at least remove the obvious non-primes...
-		if (multiplier % 2 == 0) {
-			continue;
-		}
-		if (multiplier > MIN_MULTIPLIER) {
-			break;
-		}
-	}
-	uint64_t big_secret = (uint64_t) secret * (uint64_t) multiplier;
-	if (status == SUCCESS) {
-		kprintf("%s: SUCCESS (%llu)\n", name, big_secret);
-	} else {	
-		kprintf("%s: FAIL (%llu)\n", name, big_secret);
-	}
-	return;
+
+int
+ksecprintf(const char * secret, const char * msg, const char * name)
+{
+	char *hash;
+	char *salt;
+	int res;
+
+	res = hmac_salted(msg, strlen(msg), secret, strlen(secret), &hash, &salt);
+	if (res)
+		return -res;
+
+	res = kprintf("(%s, %s, %s, %s: %s)\n", name, hash, salt, name, msg);
+
+	kfree(hash);
+	kfree(salt);
+
+	return res;
 }
+
 #endif
 
 /*