1 files changed, 61 insertions, 0 deletions
diff --git a/src/crypto/issue21104_test.go b/src/crypto/issue21104_test.go
new file mode 100644
index 0000000..b4276df
--- /dev/null
+++ b/src/crypto/issue21104_test.go
@@ -0,0 +1,61 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rc4"
+	"testing"
+)
+
+func TestRC4OutOfBoundsWrite(t *testing.T) {
+	// This cipherText is encrypted "0123456789"
+	cipherText := []byte{238, 41, 187, 114, 151, 2, 107, 13, 178, 63}
+	cipher, err := rc4.NewCipher([]byte{0})
+	if err != nil {
+		panic(err)
+	}
+	test(t, "RC4", cipherText, cipher.XORKeyStream)
+}
+func TestCTROutOfBoundsWrite(t *testing.T) {
+	testBlock(t, "CTR", cipher.NewCTR)
+}
+func TestOFBOutOfBoundsWrite(t *testing.T) {
+	testBlock(t, "OFB", cipher.NewOFB)
+}
+func TestCFBEncryptOutOfBoundsWrite(t *testing.T) {
+	testBlock(t, "CFB Encrypt", cipher.NewCFBEncrypter)
+}
+func TestCFBDecryptOutOfBoundsWrite(t *testing.T) {
+	testBlock(t, "CFB Decrypt", cipher.NewCFBDecrypter)
+}
+func testBlock(t *testing.T, name string, newCipher func(cipher.Block, []byte) cipher.Stream) {
+	// This cipherText is encrypted "0123456789"
+	cipherText := []byte{86, 216, 121, 231, 219, 191, 26, 12, 176, 117}
+	var iv, key [16]byte
+	block, err := aes.NewCipher(key[:])
+	if err != nil {
+		panic(err)
+	}
+	stream := newCipher(block, iv[:])
+	test(t, name, cipherText, stream.XORKeyStream)
+}
+func test(t *testing.T, name string, cipherText []byte, xor func([]byte, []byte)) {
+	want := "abcdefghij"
+	plainText := []byte(want)
+	shorterLen := len(cipherText) / 2
+	defer func() {
+		err := recover()
+		if err == nil {
+			t.Errorf("%v XORKeyStream expected to panic on len(dst) < len(src), but didn't", name)
+		}
+		const plain = "0123456789"
+		if plainText[shorterLen] == plain[shorterLen] {
+			t.Errorf("%v XORKeyStream did out of bounds write, want %v, got %v", name, want, string(plainText))
+		}
+	}()
+	xor(plainText[:shorterLen], cipherText)
+}