Added sha256 hash function and hmac functions (with and without salt) to the kernel

and userspace.

In userspace, this is accessed through #include <secure.h>
In the kernel, this is access through #include <kern/secure.h>

There is a unit test for this (hm1) that computes the hmac and compares it to
the known value.  The salted vesion tested offline.

-----

Also, fixed usespace compile issue with not changing KERNEL_SECRET => SECRET.

kern/include/kern/secure.h

@@ -0,0 +1,18 @@
+#ifndef _KERN_SECURE_H_
+#define _KERN_SECURE_H_
+
+/*
+ * Compute the FIPS 198-1 complient HMAC of msg using SHA256.
+ *
+ * hmac_with_salt uses a salted key and sets salt_str to this value (in hex). 
+ * Both functions below create hash_str with the hex readable version of the hash.
+ *
+ * Callers need to free hash_str (and salt_str) when done.
+ */
+int hmac(const char *msg, size_t msg_len, const char *key, size_t key_len, 
+		char **hash_str);
+
+int hmac_salted(const char *msg, size_t msg_len, const char *key, size_t key_len, 
+		char **hash_str, char **salt_str);
+
+#endif //_KERN_SECURE_H_

kern/include/test.h

@@ -96,6 +96,9 @@ int longstress(int, char **);
 int createstress(int, char **);
 int printfile(int, char **);
 
+/* HMAC/hash tests */
+int hmacu1(int, char**);
+
 /* other tests */
 int kmalloctest(int, char **);
 int kmallocstress(int, char **);