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/test/hmacunit.c

@@ -0,0 +1,99 @@
+/*
+ * Copyright (c) 2015
+ *	The President and Fellows of Harvard College.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <types.h>
+#include <lib.h>
+#include <spinlock.h>
+#include <synch.h>
+#include <thread.h>
+#include <current.h>
+#include <clock.h>
+#include <test.h>
+#include <kern/secure.h>
+
+/*
+ * Unit tests for hmac/sha256 hashing.
+ */
+
+////////////////////////////////////////////////////////////
+// support code
+
+static
+void
+ok(void)
+{
+	kprintf("Test passed.\n");
+}
+
+/*
+ * Unit test 1
+ *
+ * Test some known msg/key/hashes to make sure we produce the
+ * right results.
+ */
+static const char *plaintext1[] = {
+	"The quick brown fox jumps over the lazy dog",
+	"The only people for me are the mad ones",
+	"I don't exactly know what I mean by that, but I mean it.",
+};
+
+static const char *keys1[] = {
+	"xqWmgzbvGuLIeeKOrwMA",
+	"ZxuvolLXL7C68pDjsclX",
+	"PYeuVzKuB03awYDgJotS",
+};
+
+static const char *hashes1[] = {
+	"251ab1da03c94435daf44898fcd11606669e222270e4ac90d04a18a9df8fdfd6",
+	"75bbf48c53ccba08c244447ef7eff2e0a02f23acfdac6502282ec431823fb393",
+	"6d7d2b5eabcda504f26de7547185483b19f9953a6eaeec6c364bb45e20b28598",
+};
+
+#define N_TESTS_1 3
+
+int
+hmacu1(int nargs, char **args)
+{
+	char *hash;
+	int res;
+
+	(void)nargs; (void)args;
+	int i;
+	for (i = 0; i < N_TESTS_1; i++)
+	{
+		res = hmac(plaintext1[i], strlen(plaintext1[i]), keys1[i], strlen(keys1[i]), &hash);
+		KASSERT(!res);
+		KASSERT(strcmp(hash, hashes1[i]) == 0);
+		kfree(hash);
+	}
+
+	ok();
+	/* clean up */
+	return 0;
+}