diff --git a/crypto/bn/check_bn_tests.go b/crypto/bn/check_bn_tests.go
new file mode 100644
index 00000000..61deee27
--- /dev/null
+++ b/crypto/bn/check_bn_tests.go
@@ -0,0 +1,221 @@
+// 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 (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"math/big"
+	"os"
+	"strings"
+)
+
+type test struct {
+	LineNumber int
+	Type       string
+	Values     map[string]*big.Int
+}
+
+type testScanner struct {
+	scanner *bufio.Scanner
+	lineNo  int
+	err     error
+	test    test
+}
+
+func newTestScanner(r io.Reader) *testScanner {
+	return &testScanner{scanner: bufio.NewScanner(r)}
+}
+
+func (s *testScanner) scanLine() bool {
+	if !s.scanner.Scan() {
+		return false
+	}
+	s.lineNo++
+	return true
+}
+
+func (s *testScanner) addAttribute(line string) (key string, ok bool) {
+	fields := strings.SplitN(line, "=", 2)
+	if len(fields) != 2 {
+		s.setError(errors.New("invalid syntax"))
+		return "", false
+	}
+
+	key = strings.TrimSpace(fields[0])
+	value := strings.TrimSpace(fields[1])
+
+	valueInt, ok := new(big.Int).SetString(value, 16)
+	if !ok {
+		s.setError(fmt.Errorf("could not parse %q", value))
+		return "", false
+	}
+	if _, dup := s.test.Values[key]; dup {
+		s.setError(fmt.Errorf("duplicate key %q", key))
+		return "", false
+	}
+	s.test.Values[key] = valueInt
+	return key, true
+}
+
+func (s *testScanner) Scan() bool {
+	s.test = test{
+		Values: make(map[string]*big.Int),
+	}
+
+	// Scan until the first attribute.
+	for {
+		if !s.scanLine() {
+			return false
+		}
+		if len(s.scanner.Text()) != 0 && s.scanner.Text()[0] != '#' {
+			break
+		}
+	}
+
+	var ok bool
+	s.test.Type, ok = s.addAttribute(s.scanner.Text())
+	if !ok {
+		return false
+	}
+	s.test.LineNumber = s.lineNo
+
+	for s.scanLine() {
+		if len(s.scanner.Text()) == 0 {
+			break
+		}
+
+		if s.scanner.Text()[0] == '#' {
+			continue
+		}
+
+		if _, ok := s.addAttribute(s.scanner.Text()); !ok {
+			return false
+		}
+	}
+	return s.scanner.Err() == nil
+}
+
+func (s *testScanner) Test() test {
+	return s.test
+}
+
+func (s *testScanner) Err() error {
+	if s.err != nil {
+		return s.err
+	}
+	return s.scanner.Err()
+}
+
+func (s *testScanner) setError(err error) {
+	s.err = fmt.Errorf("line %d: %s", s.lineNo, err)
+}
+
+func checkKeys(t test, keys ...string) bool {
+	var foundErrors bool
+
+	for _, k := range keys {
+		if _, ok := t.Values[k]; !ok {
+			fmt.Fprintf(os.Stderr, "Line %d: missing key %q.\n", t.LineNumber, k)
+			foundErrors = true
+		}
+	}
+
+	for k, _ := range t.Values {
+		var found bool
+		for _, k2 := range keys {
+			if k == k2 {
+				found = true
+				break
+			}
+		}
+		if !found {
+			fmt.Fprintf(os.Stderr, "Line %d: unexpected key %q.\n", t.LineNumber, k)
+			foundErrors = true
+		}
+	}
+
+	return !foundErrors
+}
+
+func checkResult(t test, expr, key string, r *big.Int) {
+	if t.Values[key].Cmp(r) != 0 {
+		fmt.Fprintf(os.Stderr, "Line %d: %s did not match %s.\n\tGot %s\n", t.LineNumber, expr, key, r.Text(16))
+	}
+}
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Fprintf(os.Stderr, "Usage: %s bn_tests.txt\n", os.Args[0])
+		os.Exit(1)
+	}
+
+	in, err := os.Open(os.Args[1])
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error opening %s: %s.\n", os.Args[0], err)
+		os.Exit(1)
+	}
+	defer in.Close()
+
+	scanner := newTestScanner(in)
+	for scanner.Scan() {
+		test := scanner.Test()
+		switch test.Type {
+		case "Sum":
+			if checkKeys(test, "A", "B", "Sum") {
+				r := new(big.Int).Add(test.Values["A"], test.Values["B"])
+				checkResult(test, "A + B", "Sum", r)
+			}
+		case "LShift1":
+			if checkKeys(test, "A", "LShift1") {
+				r := new(big.Int).Add(test.Values["A"], test.Values["A"])
+				checkResult(test, "A + A", "LShift1", r)
+			}
+		case "LShift":
+			if checkKeys(test, "A", "N", "LShift") {
+				r := new(big.Int).Lsh(test.Values["A"], uint(test.Values["N"].Uint64()))
+				checkResult(test, "A << N", "LShift", r)
+			}
+		case "RShift":
+			if checkKeys(test, "A", "N", "RShift") {
+				r := new(big.Int).Rsh(test.Values["A"], uint(test.Values["N"].Uint64()))
+				checkResult(test, "A >> N", "RShift", r)
+			}
+		case "Square":
+			if checkKeys(test, "A", "Square") {
+				r := new(big.Int).Mul(test.Values["A"], test.Values["A"])
+				checkResult(test, "A * A", "Square", r)
+			}
+		case "Product":
+			if checkKeys(test, "A", "B", "Product") {
+				r := new(big.Int).Mul(test.Values["A"], test.Values["B"])
+				checkResult(test, "A * B", "Product", r)
+			}
+		case "Quotient":
+			if checkKeys(test, "A", "B", "Quotient", "Remainder") {
+				q, r := new(big.Int).QuoRem(test.Values["A"], test.Values["B"], new(big.Int))
+				checkResult(test, "A / B", "Quotient", q)
+				checkResult(test, "A % B", "Remainder", r)
+			}
+		default:
+			fmt.Fprintf(os.Stderr, "Line %d: unknown test type %q.\n", test.LineNumber, test.Type)
+		}
+	}
+	if scanner.Err() != nil {
+		fmt.Fprintf(os.Stderr, "Error reading tests: %s.\n", scanner.Err())
+	}
+}