diff --git a/kernel/is_valid.c b/kernel/is_valid.c
new file mode 100644
index 0000000..69f592a
--- /dev/null
+++ b/kernel/is_valid.c
@@ -0,0 +1,162 @@
+/*
+Copyright (C) 2016-2019 The University of Notre Dame
+This software is distributed under the GNU General Public License.
+See the file LICENSE for details.
+*/
+
+#include "is_valid.h"
+#include "string.h"
+#include "kobject.h"
+#include "process.h"
+#include "kmalloc.h"
+
+// Does this string comprise a valid path?
+// Valid paths are comprised of the following characters:
+// CHARS		|	ASCII CODE
+// '-'			|	45
+// '.'			|	46
+// '/'			|	47
+// [0-9]		|	[48-57]
+// [a-z]		|	[65-90]
+// '_'			|	95
+// [A-Z]		|	[97-122]
+
+int is_valid_path(const char * s)
+{
+	int length = strlen(s);
+	for (int i = 0; i < length; i++) {
+		if (s[i] < 45) return 0;
+		if (s[i] > 57 && s[i] < 65) return 0;
+		if (s[i] > 90 && s[i] < 95) return 0;
+		if (s[i] > 95 && s[i] < 97) return 0;
+		if (s[i] > 122) return 0;
+	}
+	return 1;
+}
+
+// Does this string comprise a valid tag? 
+// CHARS		|	ASCII CODE
+// [0-9]		|	[48-57]
+// [a-z]		|	[65-90]
+// [A-Z]		|	[97-122]
+
+int is_valid_tag(const char * s)
+{
+	int length = strlen(s);
+	for (int i = 0; i < length; i++) {
+		if (s[i] < 48) return 0;
+		if (s[i] > 57 && s[i] < 65) return 0;
+		if (s[i] > 90 && s[i] < 95) return 0;
+		if (s[i] > 95 && s[i] < 97) return 0;
+		if (s[i] > 122) return 0;
+	}
+	return 1;
+}
+
+// Does this string point to a valid resource (i.e. is it a legitimate
+// tag-path concatenation)?
+// CHARS		|	ASCII CODE
+// ':'			|	58
+
+int is_valid_location(const char * s)
+{
+	int length = strlen(s);
+	char * mutable_test = kmalloc(sizeof(char) * (length+1));
+	strcpy(mutable_test, s);
+
+	int path_index = 0;
+	while (path_index < length && s[path_index] != 58) {
+		path_index += 1;
+	}
+	mutable_test[path_index++] = 0;
+
+	if (is_valid_tag(mutable_test)
+		&& is_valid_path(mutable_test + path_index)) {
+		return 1;
+	}
+	return 0;
+}
+
+// Return true if file desciptor is in range and refers to a live object.
+int is_valid_object( int fd )
+{
+	return fd>=0 && fd<PROCESS_MAX_OBJECTS && current->ktable[fd];
+}
+
+// Return true if fd valid and object is also of indicated type.
+int is_valid_object_type( int fd, kobject_type_t type )
+{
+	return is_valid_object(fd) && kobject_get_type(current->ktable[fd])==type;
+}
+
+// Return true if (ptr,length) describes a valid area in user space.
+// XXX Needs to be implemented!
+
+int is_valid_pointer( void *ptr, int length )
+{
+	return 1;
+}
+
+// Return true if string points to a valid area in user space.
+// XXX Needs to be implemented!
+
+int is_valid_string( const char *str )
+{
+	return 1;
+}
+
+#ifdef TEST
+void is_valid_test()
+{
+	printf("Testing PATH validations...\n");
+	char * s = "/root/is-valid.path";
+	if (!is_valid_path(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "abcdefghijklmnopqrstuvwxyz";
+	if (!is_valid_path(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+	if (!is_valid_path(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "0123456789";
+	if (!is_valid_path(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "/root/isn't/valid:";
+	if (is_valid_path(s))
+		printf("ERROR: Did not invalidate %s\n", s);
+
+	printf("Testing Tag Validations...\n");
+	s = "TAG";
+	if (!is_valid_tag(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "abcdefghijklmnopqrstuvwxyz";
+	if (!is_valid_tag(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+	if (!is_valid_tag(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "0123456789";
+	if (!is_valid_tag(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = ":NOT-A-TAG";
+	if (is_valid_tag(s))
+		printf("ERROR: Did not invalidate %s\n", s);
+
+	printf("Testing Location Validations...\n");
+	s = "HOME:path/to/root/dir";
+	if (!is_valid_location(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "TAG";
+	if (!is_valid_tag(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "/root/is-valid.path";
+	if (!is_valid_path(s))
+		printf("ERROR: Did not validate %s\n", s);
+	s = "BAD-TAG:p@th/:/root/dir";
+	if (is_valid_location(s))
+		printf("ERROR: Did not invalidate %s\n", s);
+
+}
+
+#endif
+