Improve CFB8 implementation (#256)

* Add CFB8 tests & benchmark

* Improve CFB8 implementation

* Cleanup code

* Speed up with copy function

* Even faster

* Fix & more tests

* Fix tests

* Fix typo

net/CFB8/cfb8.go

@@ -1,51 +1,108 @@
-// Package CFB8 is copied from https://play.golang.org/p/LTbId4b6M2
+// Package CFB8 implements CFB8 block cipher mode of operation used by Minecraft protocol.
 package CFB8
 
-import "crypto/cipher"
+import (
+	"crypto/cipher"
+	"unsafe"
+)
 
 type CFB8 struct {
 	c         cipher.Block
 	blockSize int
-	iv, tmp   []byte
+	ivPos     int
+	iv        []byte
 	de        bool
 }
 
 func NewCFB8Decrypt(c cipher.Block, iv []byte) *CFB8 {
-	cp := make([]byte, len(iv))
+	return newCFB8(c, iv, true)
-	copy(cp, iv)
-	return &CFB8{
-		c:         c,
-		blockSize: c.BlockSize(),
-		iv:        cp,
-		tmp:       make([]byte, c.BlockSize()),
-		de:        true,
-	}
 }
 
 func NewCFB8Encrypt(c cipher.Block, iv []byte) *CFB8 {
-	cp := make([]byte, len(iv))
+	return newCFB8(c, iv, false)
+}
+
+func newCFB8(c cipher.Block, iv []byte, de bool) *CFB8 {
+	cp := make([]byte, len(iv)*3)
 	copy(cp, iv)
 	return &CFB8{
 		c:         c,
 		blockSize: c.BlockSize(),
 		iv:        cp,
-		tmp:       make([]byte, c.BlockSize()),
+		de:        de,
-		de:        false,
 	}
 }
 
 func (cf *CFB8) XORKeyStream(dst, src []byte) {
-	for i := 0; i < len(src); i++ {
+	if len(dst) < len(src) {
-		val := src[i]
+		panic("cfb8: output smaller than input")
-		copy(cf.tmp, cf.iv)
+	}
-		cf.c.Encrypt(cf.iv, cf.iv)
-		val = val ^ cf.iv[0]
 
-		copy(cf.iv, cf.tmp[1:])
+	// If dst and src does not overlap in first block size,
+	// and the length of src is greater than 2*blockSize,
+	// we can use an optimized implementation.
+	if len(src) > cf.blockSize<<1 &&
+		(uintptr(unsafe.Pointer(&dst[0]))+uintptr(cf.blockSize) <= uintptr(unsafe.Pointer(&src[0])) ||
+			uintptr(unsafe.Pointer(&src[0]))+uintptr(len(src)) <= uintptr(unsafe.Pointer(&dst[0]))) {
+		// encrypt/decrypt first blockSize bytes
+		// After this, the IV will come to the same as
+		// the last blockSize of ciphertext, so
+		// we can reuse them without copy.
+		cf.XORKeyStream(dst, src[:cf.blockSize])
+		var ciphertext []byte
 		if cf.de {
-			cf.iv[15] = src[i]
+			ciphertext = src
 		} else {
-			cf.iv[15] = val
+			ciphertext = dst
+		}
+		dst = dst[cf.blockSize:]
+		src = src[cf.blockSize:]
+		iv := cf.iv
+		_ = iv[0] // bounds check hint to compiler; see golang.org/issue/14808
+		var (
+			i   int
+			val byte
+		)
+		for i, val = range src {
+			cf.c.Encrypt(iv, ciphertext[i:])
+			dst[i] = val ^ iv[0]
+		}
+		// copy the current IV for next operation
+		copy(iv, ciphertext[i+1:i+1+cf.blockSize])
+		cf.ivPos = 0
+		return
+	}
+
+	for i, val := range src {
+		posPlusBlockSize := cf.ivPos + cf.blockSize
+		// fast mod; 2*blockSize must be a non-negative integer power of 2
+		tempPos := posPlusBlockSize & (cf.blockSize<<1 - 1)
+		// reuse space to store encrypted block
+		cf.c.Encrypt(cf.iv[tempPos:], cf.iv[cf.ivPos:])
+		// Only the first byte of the encrypted block is used
+		// for encryption/decryption, other bytes are ignored.
+		val ^= cf.iv[tempPos]
+
+		if cf.ivPos == cf.blockSize<<1 {
+			// bound reached; move to next round for next operation
+			// copy next block to the start of the ring buffer
+			copy(cf.iv, cf.iv[cf.ivPos+1:])
+			// insert the encrypted byte to the end of IV
+			if cf.de {
+				cf.iv[cf.blockSize-1] = src[i]
+			} else {
+				cf.iv[cf.blockSize-1] = val
+			}
+			cf.ivPos = 0
+		} else {
+			// insert the encrypted byte to the end of IV
+			if cf.de {
+				cf.iv[posPlusBlockSize] = src[i]
+			} else {
+				cf.iv[posPlusBlockSize] = val
+			}
+			// move to next block
+			cf.ivPos += 1
 		}
 
 		dst[i] = val

net/CFB8/cfb8_test.go

@@ -0,0 +1,186 @@
+package CFB8
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/rand"
+	"encoding/hex"
+	"testing"
+)
+
+// cfb8Tests contains the test vectors from
+// https://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf, section
+// F.3.7. Modified for Minecraft CFB8 tests.
+var cfb8Tests = []struct {
+	key, iv, plaintext, ciphertext string
+}{
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"000102030405060708090a0b0c0d0e0f",
+		"6bc1bee22e409f96e93d7e117393172a",
+		"3b79424c9c0dd436bace9e0ed4586a4f",
+	},
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"3B3FD92EB72DAD20333449F8E83CFB4A",
+		"ae2d8a571e03ac9c9eb76fac45af8e51",
+		"c8b0723943d71f61a2e5b0e8cedf87c8",
+	},
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"C8A64537A0B3A93FCDE3CDAD9F1CE58B",
+		"30c81c46a35ce411e5fbc1191a0a52ef",
+		"260d20e9395d3501067286d3a2a7002f",
+	},
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"26751F67A3CBB140B1808CF187A4F4DF",
+		"f69f2445df4f9b17ad2b417be66c3710",
+		"c0af633cd9c599309f924802af599ee6",
+	},
+	{
+		"2b7e151628aed2a6abf7158809cf4f3c",
+		"000102030405060708090a0b0c0d0e0f",
+		"0ecbd6d36cd12962ce671b4d96fb95aaa902096aeac366e13a6ae57c05d48673cf320c626689d05548f65fd6a108630c1d4e3aab543b006823c7a9422e97c0431587537c384f99a11488ffd9b2e9b46f49005a7e5cef64e27e2de3cf3fb87c1524766601",
+		"5efb6f6b93cf5f0e135a0c932f59f9aaa2276e4b06cd4f5edca4baba735ac7708dd7c0f9e92c6b89d2245b0d9a6356b0e98529cd45e56df22e914ef9e0792facaab707af90c13162bfad06a240eb6adcbf3365fd84a003f8083f4662a7a27232c72c6c0c",
+	},
+}
+
+func TestCFB8VectorsNonOverlapping(t *testing.T) {
+	for i, test := range cfb8Tests {
+		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 := NewCFB8Encrypt(block, iv)
+		if len(plaintext) > 50 {
+			cfb.XORKeyStream(ciphertext, plaintext[:len(plaintext)/2])
+			cfb.XORKeyStream(ciphertext[len(plaintext)/2:], plaintext[len(plaintext)/2:])
+		} else {
+			cfb.XORKeyStream(ciphertext, plaintext)
+		}
+
+		if !bytes.Equal(ciphertext, expected) {
+			t.Errorf("#%d: wrong output: got %x, expected %x", i, ciphertext, expected)
+		}
+
+		cfbdec := NewCFB8Decrypt(block, iv)
+		plaintextCopy := make([]byte, len(ciphertext))
+		if len(ciphertext) > 50 {
+			cfbdec.XORKeyStream(plaintextCopy, ciphertext[:len(ciphertext)/2])
+			cfbdec.XORKeyStream(plaintextCopy[len(ciphertext)/2:], ciphertext[len(ciphertext)/2:])
+		} else {
+			cfbdec.XORKeyStream(plaintextCopy, ciphertext)
+		}
+
+		if !bytes.Equal(plaintextCopy, plaintext) {
+			t.Errorf("#%d: wrong plaintext: got %x, expected %x", i, plaintextCopy, plaintext)
+		}
+	}
+}
+
+func TestCFB8VectorsOverlapped(t *testing.T) {
+	for i, test := range cfb8Tests {
+		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)
+		}
+
+		buf := make([]byte, len(plaintext))
+		copy(buf, plaintext)
+		cfb := NewCFB8Encrypt(block, iv)
+		if len(buf) > 50 {
+			cfb.XORKeyStream(buf, buf[:len(buf)/2])
+			cfb.XORKeyStream(buf[len(buf)/2:], buf[len(buf)/2:])
+		} else {
+			cfb.XORKeyStream(buf, buf)
+		}
+
+		if !bytes.Equal(buf, expected) {
+			t.Errorf("#%d: wrong output: got %x, expected %x", i, buf, expected)
+		}
+
+		cfbdec := NewCFB8Decrypt(block, iv)
+		if len(buf) > 50 {
+			cfbdec.XORKeyStream(buf, buf[:len(buf)/2])
+			cfbdec.XORKeyStream(buf[len(buf)/2:], buf[len(buf)/2:])
+		} else {
+			cfbdec.XORKeyStream(buf, buf)
+		}
+
+		if !bytes.Equal(buf, plaintext) {
+			t.Errorf("#%d: wrong plaintext: got %x, expected %x", i, buf, plaintext)
+		}
+	}
+}
+
+func BenchmarkCFB8AES1KOverlapped(b *testing.B) {
+	var key [16]byte
+	var iv [16]byte
+	rand.Read(key[:])
+	rand.Read(iv[:])
+	buf := make([]byte, 1024)
+	aes, _ := aes.NewCipher(key[:])
+	stream := NewCFB8Encrypt(aes, iv[:])
+
+	b.SetBytes(int64(len(buf)))
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		stream.XORKeyStream(buf, buf)
+	}
+}
+
+func BenchmarkCFB8AES1KNonOverlapping(b *testing.B) {
+	var key [16]byte
+	var iv [16]byte
+	rand.Read(key[:])
+	rand.Read(iv[:])
+	buf := make([]byte, 1024)
+	buf2 := make([]byte, 1024)
+	aes, _ := aes.NewCipher(key[:])
+	stream := NewCFB8Encrypt(aes, iv[:])
+
+	b.SetBytes(int64(len(buf)))
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		stream.XORKeyStream(buf2, buf)
+	}
+}