diff --git a/util/diff_asm.go b/util/diff_asm.go
new file mode 100644
index 00000000..0a0888b0
--- /dev/null
+++ b/util/diff_asm.go
@@ -0,0 +1,112 @@
+/* Copyright (c) 2016, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"syscall"
+)
+
+var (
+	boringsslDir = flag.String("boringssl", ".", "The path to the BoringSSL checkout.")
+	opensslDir   = flag.String("openssl", filepath.Join("..", "openssl"), "The path to the OpenSSL checkout.")
+)
+
+func mapName(path string) string {
+	switch filepath.ToSlash(path) {
+	case "crypto/rand/asm/rdrand-x86_64.pl":
+		return ""
+	case "crypto/ec/asm/p256-x86_64-asm.pl":
+		return filepath.FromSlash("crypto/ec/asm/ecp_nistz256-x86_64.pl")
+	}
+	return path
+}
+
+func diff(from, to string) error {
+	cmd := exec.Command("diff", "-u", "--", from, to)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	// diff returns exit code 1 if the files differ but it was otherwise
+	// successful.
+	if exitError, ok := err.(*exec.ExitError); ok && exitError.Sys().(syscall.WaitStatus).ExitStatus() == 1 {
+		return nil
+	}
+	return err
+}
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "Usage: diff_asm [flag...] [filter...]\n")
+		fmt.Fprintf(os.Stderr, "Filter arguments limit to assembly files which match arguments.\n")
+		fmt.Fprintf(os.Stderr, "If not using a filter, piping to `diffstat` may be useful.\n\n")
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	// Find all the assembly files.
+	var files []string
+	err := filepath.Walk(*boringsslDir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return nil
+		}
+
+		path, err = filepath.Rel(*boringsslDir, path)
+		if err != nil {
+			return err
+		}
+
+		dir := filepath.Base(filepath.Dir(path))
+		if !info.IsDir() && (dir == "asm" || dir == "perlasm") && strings.HasSuffix(filepath.Base(path), ".pl") {
+			files = append(files, path)
+		}
+
+		return nil
+	})
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error finding assembly: %s\n", err)
+		os.Exit(1)
+	}
+
+	for _, file := range files {
+		opensslFile := mapName(file)
+		if len(opensslFile) == 0 {
+			continue
+		}
+
+		if flag.NArg() > 0 {
+			var found bool
+			for _, arg := range flag.Args() {
+				if strings.Contains(file, arg) {
+					found = true
+					break
+				}
+			}
+			if !found {
+				continue
+			}
+		}
+
+		if err := diff(filepath.Join(*opensslDir, opensslFile), filepath.Join(*boringsslDir, file)); err != nil {
+			fmt.Fprintf(os.Stderr, "Error comparing %s: %s\n", file, err)
+			os.Exit(1)
+		}
+	}
+}