crypto/cipher: add CFB test vectors.

Fixes #8576.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/136720043

src/pkg/crypto/cipher/cfb_test.go

@@ -9,10 +9,85 @@ import (
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/rand"
+	"encoding/hex"
 	"testing"
 )
 
-func TestCFB(t *testing.T) {
+// cfbTests contains the test vectors from
+// http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf, section
+// F.3.13.
+var cfbTests = []struct {
+	key, iv, plaintext, ciphertext string
+}{
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"000102030405060708090a0b0c0d0e0f",
+		"6bc1bee22e409f96e93d7e117393172a",
+		"3b3fd92eb72dad20333449f8e83cfb4a",
+	},
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"3B3FD92EB72DAD20333449F8E83CFB4A",
+		"ae2d8a571e03ac9c9eb76fac45af8e51",
+		"c8a64537a0b3a93fcde3cdad9f1ce58b",
+	},
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"C8A64537A0B3A93FCDE3CDAD9F1CE58B",
+		"30c81c46a35ce411e5fbc1191a0a52ef",
+		"26751f67a3cbb140b1808cf187a4f4df",
+	},
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"26751F67A3CBB140B1808CF187A4F4DF",
+		"f69f2445df4f9b17ad2b417be66c3710",
+		"c04b05357c5d1c0eeac4c66f9ff7f2e6",
+	},
+}
+
+func TestCFBVectors(t *testing.T) {
+	for i, test := range cfbTests {
+		key, err := hex.DecodeString(test.key)
+		if err != nil {
+			t.Fatal(err)
+		}
+		iv, err := hex.DecodeString(test.iv)
+		if err != nil {
+			t.Fatal(err)
+		}
+		plaintext, err := hex.DecodeString(test.plaintext)
+		if err != nil {
+			t.Fatal(err)
+		}
+		expected, err := hex.DecodeString(test.ciphertext)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		block, err := aes.NewCipher(key)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		ciphertext := make([]byte, len(plaintext))
+		cfb := cipher.NewCFBEncrypter(block, iv)
+		cfb.XORKeyStream(ciphertext, plaintext)
+
+		if !bytes.Equal(ciphertext, expected) {
+			t.Errorf("#%d: wrong output: got %x, expected %x", i, ciphertext, expected)
+		}
+
+		cfbdec := cipher.NewCFBDecrypter(block, iv)
+		plaintextCopy := make([]byte, len(ciphertext))
+		cfbdec.XORKeyStream(plaintextCopy, ciphertext)
+
+		if !bytes.Equal(plaintextCopy, plaintextCopy) {
+			t.Errorf("#%d: wrong plaintext: got %x, expected %x", i, plaintextCopy, plaintext)
+		}
+	}
+}
+
+func TestCFBInverse(t *testing.T) {
 	block, err := aes.NewCipher(commonKey128)
 	if err != nil {
 		t.Error(err)