crypto/tls: implement TLS 1.3 cryptographic computations

Vendors golang.org/x/crypto/hkdf at e84da0312774c21d64ee2317962ef669b27ffb41

Updates #9671

Change-Id: I2610c4a66756e2a6f21f9823dcbe39edd9c9ea21
Reviewed-on: https://go-review.googlesource.com/c/145298Reviewed-by: Adam Langley <agl@golang.org>

src/crypto/tls/key_schedule.go

+// Copyright 2018 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 tls
+
+import (
+	"golang_org/x/crypto/cryptobyte"
+	"golang_org/x/crypto/hkdf"
+	"hash"
+)
+
+// This file contains the functions necessary to compute the TLS 1.3 key
+// schedule. See RFC 8446, Section 7.
+
+const (
+	resumptionBinderLabel         = "res binder"
+	clientHandshakeTrafficLabel   = "c hs traffic"
+	serverHandshakeTrafficLabel   = "s hs traffic"
+	clientApplicationTrafficLabel = "c ap traffic"
+	serverApplicationTrafficLabel = "s ap traffic"
+	exporterLabel                 = "exp master"
+	resumptionLabel               = "res master"
+	trafficUpdateLabel            = "traffic upd"
+)
+
+// expandLabel implements HKDF-Expand-Label from RFC 8446, Section 7.1.
+func (c *cipherSuiteTLS13) expandLabel(secret []byte, label string, context []byte, length int) []byte {
+	var hkdfLabel cryptobyte.Builder
+	hkdfLabel.AddUint16(uint16(length))
+	hkdfLabel.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
+		b.AddBytes([]byte("tls13 "))
+		b.AddBytes([]byte(label))
+	})
+	hkdfLabel.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
+		b.AddBytes(context)
+	})
+	out := make([]byte, length)
+	n, err := hkdf.Expand(c.hash.New, secret, hkdfLabel.BytesOrPanic()).Read(out)
+	if err != nil || n != length {
+		panic("tls: HKDF-Expand-Label invocation failed unexpectedly")
+	}
+	return out
+}
+
+// deriveSecret implements Derive-Secret from RFC 8446, Section 7.1.
+func (c *cipherSuiteTLS13) deriveSecret(secret []byte, label string, transcript hash.Hash) []byte {
+	if transcript == nil {
+		transcript = c.hash.New()
+	}
+	return c.expandLabel(secret, label, transcript.Sum(nil), c.hash.Size())
+}
+
+// extract implements HKDF-Extract with the cipher suite hash.
+func (c *cipherSuiteTLS13) extract(newSecret, currentSecret []byte) []byte {
+	if newSecret == nil {
+		newSecret = make([]byte, c.hash.Size())
+	}
+	return hkdf.Extract(c.hash.New, newSecret, currentSecret)
+}
+
+// nextTrafficSecret generates the next traffic secret, given the current one,
+// according to RFC 8446, Section 7.2.
+func (c *cipherSuiteTLS13) nextTrafficSecret(trafficSecret []byte) []byte {
+	return c.expandLabel(trafficSecret, trafficUpdateLabel, nil, c.hash.Size())
+}
+
+// trafficKey generates traffic keys according to RFC 8446, Section 7.3.
+func (c *cipherSuiteTLS13) trafficKey(trafficSecret []byte) (key, iv []byte) {
+	key = c.expandLabel(trafficSecret, "key", nil, c.keyLen)
+	iv = c.expandLabel(trafficSecret, "iv", nil, aeadNonceLength)
+	return
+}
+
+// exportKeyingMaterial implements RFC5705 exporters for TLS 1.3 according to
+// RFC 8446, Section 7.5.
+func (c *cipherSuiteTLS13) exportKeyingMaterial(masterSecret []byte, transcript hash.Hash) func(string, []byte, int) ([]byte, error) {
+	expMasterSecret := c.deriveSecret(masterSecret, exporterLabel, transcript)
+	return func(label string, context []byte, length int) ([]byte, error) {
+		secret := c.deriveSecret(expMasterSecret, label, nil)
+		h := c.hash.New()
+		h.Write(context)
+		return c.expandLabel(secret, "exporter", h.Sum(nil), length), nil
+	}
+}

src/crypto/tls/key_schedule_test.go

+// Copyright 2018 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 tls
+
+import (
+	"bytes"
+	"encoding/hex"
+	"hash"
+	"strings"
+	"testing"
+	"unicode"
+)
+
+// This file contains tests derived from draft-ietf-tls-tls13-vectors-07.
+
+func parseVector(v string) []byte {
+	v = strings.Map(func(c rune) rune {
+		if unicode.IsSpace(c) {
+			return -1
+		}
+		return c
+	}, v)
+	parts := strings.Split(v, ":")
+	v = parts[len(parts)-1]
+	res, err := hex.DecodeString(v)
+	if err != nil {
+		panic(err)
+	}
+	return res
+}
+
+func TestDeriveSecret(t *testing.T) {
+	chTranscript := cipherSuitesTLS13[0].hash.New()
+	chTranscript.Write(parseVector(`
+	payload (512 octets):  01 00 01 fc 03 03 1b c3 ce b6 bb e3 9c ff
+	93 83 55 b5 a5 0a db 6d b2 1b 7a 6a f6 49 d7 b4 bc 41 9d 78 76
+	48 7d 95 00 00 06 13 01 13 03 13 02 01 00 01 cd 00 00 00 0b 00
+	09 00 00 06 73 65 72 76 65 72 ff 01 00 01 00 00 0a 00 14 00 12
+	00 1d 00 17 00 18 00 19 01 00 01 01 01 02 01 03 01 04 00 33 00
+	26 00 24 00 1d 00 20 e4 ff b6 8a c0 5f 8d 96 c9 9d a2 66 98 34
+	6c 6b e1 64 82 ba dd da fe 05 1a 66 b4 f1 8d 66 8f 0b 00 2a 00
+	00 00 2b 00 03 02 03 04 00 0d 00 20 00 1e 04 03 05 03 06 03 02
+	03 08 04 08 05 08 06 04 01 05 01 06 01 02 01 04 02 05 02 06 02
+	02 02 00 2d 00 02 01 01 00 1c 00 02 40 01 00 15 00 57 00 00 00
+	00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+	00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+	00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+	00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+	00 29 00 dd 00 b8 00 b2 2c 03 5d 82 93 59 ee 5f f7 af 4e c9 00
+	00 00 00 26 2a 64 94 dc 48 6d 2c 8a 34 cb 33 fa 90 bf 1b 00 70
+	ad 3c 49 88 83 c9 36 7c 09 a2 be 78 5a bc 55 cd 22 60 97 a3 a9
+	82 11 72 83 f8 2a 03 a1 43 ef d3 ff 5d d3 6d 64 e8 61 be 7f d6
+	1d 28 27 db 27 9c ce 14 50 77 d4 54 a3 66 4d 4e 6d a4 d2 9e e0
+	37 25 a6 a4 da fc d0 fc 67 d2 ae a7 05 29 51 3e 3d a2 67 7f a5
+	90 6c 5b 3f 7d 8f 92 f2 28 bd a4 0d da 72 14 70 f9 fb f2 97 b5
+	ae a6 17 64 6f ac 5c 03 27 2e 97 07 27 c6 21 a7 91 41 ef 5f 7d
+	e6 50 5e 5b fb c3 88 e9 33 43 69 40 93 93 4a e4 d3 57 fa d6 aa
+	cb 00 21 20 3a dd 4f b2 d8 fd f8 22 a0 ca 3c f7 67 8e f5 e8 8d
+	ae 99 01 41 c5 92 4d 57 bb 6f a3 1b 9e 5f 9d`))
+
+	type args struct {
+		secret     []byte
+		label      string
+		transcript hash.Hash
+	}
+	tests := []struct {
+		name string
+		args args
+		want []byte
+	}{
+		{
+			`derive secret for handshake "tls13 derived"`,
+			args{
+				parseVector(`PRK (32 octets):  33 ad 0a 1c 60 7e c0 3b 09 e6 cd 98 93 68 0c e2
+				10 ad f3 00 aa 1f 26 60 e1 b2 2e 10 f1 70 f9 2a`),
+				"derived",
+				nil,
+			},
+			parseVector(`expanded (32 octets):  6f 26 15 a1 08 c7 02 c5 67 8f 54 fc 9d ba
+			b6 97 16 c0 76 18 9c 48 25 0c eb ea c3 57 6c 36 11 ba`),
+		},
+		{
+			`derive secret "tls13 c e traffic"`,
+			args{
+				parseVector(`PRK (32 octets):  9b 21 88 e9 b2 fc 6d 64 d7 1d c3 29 90 0e 20 bb
+				41 91 50 00 f6 78 aa 83 9c bb 79 7c b7 d8 33 2c`),
+				"c e traffic",
+				chTranscript,
+			},
+			parseVector(`expanded (32 octets):  3f bb e6 a6 0d eb 66 c3 0a 32 79 5a ba 0e
+			ff 7e aa 10 10 55 86 e7 be 5c 09 67 8d 63 b6 ca ab 62`),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			c := cipherSuitesTLS13[0]
+			if got := c.deriveSecret(tt.args.secret, tt.args.label, tt.args.transcript); !bytes.Equal(got, tt.want) {
+				t.Errorf("cipherSuiteTLS13.deriveSecret() = % x, want % x", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestTrafficKey(t *testing.T) {
+	trafficSecret := parseVector(
+		`PRK (32 octets):  b6 7b 7d 69 0c c1 6c 4e 75 e5 42 13 cb 2d 37 b4
+		e9 c9 12 bc de d9 10 5d 42 be fd 59 d3 91 ad 38`)
+	wantKey := parseVector(
+		`key expanded (16 octets):  3f ce 51 60 09 c2 17 27 d0 f2 e4 e8 6e
+		e4 03 bc`)
+	wantIV := parseVector(
+		`iv expanded (12 octets):  5d 31 3e b2 67 12 76 ee 13 00 0b 30`)
+
+	c := cipherSuitesTLS13[0]
+	gotKey, gotIV := c.trafficKey(trafficSecret)
+	if !bytes.Equal(gotKey, wantKey) {
+		t.Errorf("cipherSuiteTLS13.trafficKey() gotKey = % x, want % x", gotKey, wantKey)
+	}
+	if !bytes.Equal(gotIV, wantIV) {
+		t.Errorf("cipherSuiteTLS13.trafficKey() gotIV = % x, want % x", gotIV, wantIV)
+	}
+}
+
+func TestExtract(t *testing.T) {
+	type args struct {
+		newSecret     []byte
+		currentSecret []byte
+	}
+	tests := []struct {
+		name string
+		args args
+		want []byte
+	}{
+		{
+			`extract secret "early"`,
+			args{
+				nil,
+				nil,
+			},
+			parseVector(`secret (32 octets):  33 ad 0a 1c 60 7e c0 3b 09 e6 cd 98 93 68 0c
+			e2 10 ad f3 00 aa 1f 26 60 e1 b2 2e 10 f1 70 f9 2a`),
+		},
+		{
+			`extract secret "master"`,
+			args{
+				nil,
+				parseVector(`salt (32 octets):  43 de 77 e0 c7 77 13 85 9a 94 4d b9 db 25 90 b5
+				31 90 a6 5b 3e e2 e4 f1 2d d7 a0 bb 7c e2 54 b4`),
+			},
+			parseVector(`secret (32 octets):  18 df 06 84 3d 13 a0 8b f2 a4 49 84 4c 5f 8a
+			47 80 01 bc 4d 4c 62 79 84 d5 a4 1d a8 d0 40 29 19`),
+		},
+		{
+			`extract secret "handshake"`,
+			args{
+				parseVector(`IKM (32 octets):  8b d4 05 4f b5 5b 9d 63 fd fb ac f9 f0 4b 9f 0d
+				35 e6 d6 3f 53 75 63 ef d4 62 72 90 0f 89 49 2d`),
+				parseVector(`salt (32 octets):  6f 26 15 a1 08 c7 02 c5 67 8f 54 fc 9d ba b6 97
+				16 c0 76 18 9c 48 25 0c eb ea c3 57 6c 36 11 ba`),
+			},
+			parseVector(`secret (32 octets):  1d c8 26 e9 36 06 aa 6f dc 0a ad c1 2f 74 1b
+			01 04 6a a6 b9 9f 69 1e d2 21 a9 f0 ca 04 3f be ac`),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			c := cipherSuitesTLS13[0]
+			if got := c.extract(tt.args.newSecret, tt.args.currentSecret); !bytes.Equal(got, tt.want) {
+				t.Errorf("cipherSuiteTLS13.extract() = % x, want % x", got, tt.want)
+			}
+		})
+	}
+}

src/go/build/deps_test.go

@@ -389,7 +389,7 @@ var pkgDeps = map[string][]string{
 
 	// SSL/TLS.
 	"crypto/tls": {
-		"L4", "CRYPTO-MATH", "OS", "golang_org/x/crypto/cryptobyte",
+		"L4", "CRYPTO-MATH", "OS", "golang_org/x/crypto/cryptobyte", "golang_org/x/crypto/hkdf",
 		"container/list", "crypto/x509", "encoding/pem", "net", "syscall",
 	},
 	"crypto/x509": {

src/vendor/golang_org/x/crypto/hkdf/example_test.go

+// Copyright 2014 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 hkdf_test
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/sha256"
+	"fmt"
+	"io"
+
+	"golang_org/x/crypto/hkdf"
+)
+
+// Usage example that expands one master secret into three other
+// cryptographically secure keys.
+func Example_usage() {
+	// Underlying hash function for HMAC.
+	hash := sha256.New
+
+	// Cryptographically secure master secret.
+	secret := []byte{0x00, 0x01, 0x02, 0x03} // i.e. NOT this.
+
+	// Non-secret salt, optional (can be nil).
+	// Recommended: hash-length random value.
+	salt := make([]byte, hash().Size())
+	if _, err := rand.Read(salt); err != nil {
+		panic(err)
+	}
+
+	// Non-secret context info, optional (can be nil).
+	info := []byte("hkdf example")
+
+	// Generate three 128-bit derived keys.
+	hkdf := hkdf.New(hash, secret, salt, info)
+
+	var keys [][]byte
+	for i := 0; i < 3; i++ {
+		key := make([]byte, 16)
+		if _, err := io.ReadFull(hkdf, key); err != nil {
+			panic(err)
+		}
+		keys = append(keys, key)
+	}
+
+	for i := range keys {
+		fmt.Printf("Key #%d: %v\n", i+1, !bytes.Equal(keys[i], make([]byte, 16)))
+	}
+
+	// Output:
+	// Key #1: true
+	// Key #2: true
+	// Key #3: true
+}

src/vendor/golang_org/x/crypto/hkdf/hkdf.go

+// Copyright 2014 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 hkdf implements the HMAC-based Extract-and-Expand Key Derivation
+// Function (HKDF) as defined in RFC 5869.
+//
+// HKDF is a cryptographic key derivation function (KDF) with the goal of
+// expanding limited input keying material into one or more cryptographically
+// strong secret keys.
+package hkdf // import "golang.org/x/crypto/hkdf"
+
+import (
+	"crypto/hmac"
+	"errors"
+	"hash"
+	"io"
+)
+
+// Extract generates a pseudorandom key for use with Expand from an input secret
+// and an optional independent salt.
+//
+// Only use this function if you need to reuse the extracted key with multiple
+// Expand invocations and different context values. Most common scenarios,
+// including the generation of multiple keys, should use New instead.
+func Extract(hash func() hash.Hash, secret, salt []byte) []byte {
+	if salt == nil {
+		salt = make([]byte, hash().Size())
+	}
+	extractor := hmac.New(hash, salt)
+	extractor.Write(secret)
+	return extractor.Sum(nil)
+}
+
+type hkdf struct {
+	expander hash.Hash
+	size     int
+
+	info    []byte
+	counter byte
+
+	prev []byte
+	buf  []byte
+}
+
+func (f *hkdf) Read(p []byte) (int, error) {
+	// Check whether enough data can be generated
+	need := len(p)
+	remains := len(f.buf) + int(255-f.counter+1)*f.size
+	if remains < need {
+		return 0, errors.New("hkdf: entropy limit reached")
+	}
+	// Read any leftover from the buffer
+	n := copy(p, f.buf)
+	p = p[n:]
+
+	// Fill the rest of the buffer
+	for len(p) > 0 {
+		f.expander.Reset()
+		f.expander.Write(f.prev)
+		f.expander.Write(f.info)
+		f.expander.Write([]byte{f.counter})
+		f.prev = f.expander.Sum(f.prev[:0])
+		f.counter++
+
+		// Copy the new batch into p
+		f.buf = f.prev
+		n = copy(p, f.buf)
+		p = p[n:]
+	}
+	// Save leftovers for next run
+	f.buf = f.buf[n:]
+
+	return need, nil
+}
+
+// Expand returns a Reader, from which keys can be read, using the given
+// pseudorandom key and optional context info, skipping the extraction step.
+//
+// The pseudorandomKey should have been generated by Extract, or be a uniformly
+// random or pseudorandom cryptographically strong key. See RFC 5869, Section
+// 3.3. Most common scenarios will want to use New instead.
+func Expand(hash func() hash.Hash, pseudorandomKey, info []byte) io.Reader {
+	expander := hmac.New(hash, pseudorandomKey)
+	return &hkdf{expander, expander.Size(), info, 1, nil, nil}
+}
+
+// New returns a Reader, from which keys can be read, using the given hash,
+// secret, salt and context info. Salt and info can be nil.
+func New(hash func() hash.Hash, secret, salt, info []byte) io.Reader {
+	prk := Extract(hash, secret, salt)
+	return Expand(hash, prk, info)
+}

src/vendor/golang_org/x/crypto/hkdf/hkdf_test.go

+// Copyright 2014 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 hkdf
+
+import (
+	"bytes"
+	"crypto/md5"
+	"crypto/sha1"
+	"crypto/sha256"
+	"crypto/sha512"
+	"hash"
+	"io"
+	"testing"
+)
+
+type hkdfTest struct {
+	hash   func() hash.Hash
+	master []byte
+	salt   []byte
+	prk    []byte
+	info   []byte
+	out    []byte
+}
+
+var hkdfTests = []hkdfTest{
+	// Tests from RFC 5869
+	{
+		sha256.New,
+		[]byte{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+		},
+		[]byte{
+			0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			0x08, 0x09, 0x0a, 0x0b, 0x0c,
+		},
+		[]byte{
+			0x07, 0x77, 0x09, 0x36, 0x2c, 0x2e, 0x32, 0xdf,
+			0x0d, 0xdc, 0x3f, 0x0d, 0xc4, 0x7b, 0xba, 0x63,
+			0x90, 0xb6, 0xc7, 0x3b, 0xb5, 0x0f, 0x9c, 0x31,
+			0x22, 0xec, 0x84, 0x4a, 0xd7, 0xc2, 0xb3, 0xe5,
+		},
+		[]byte{
+			0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+			0xf8, 0xf9,
+		},
+		[]byte{
+			0x3c, 0xb2, 0x5f, 0x25, 0xfa, 0xac, 0xd5, 0x7a,
+			0x90, 0x43, 0x4f, 0x64, 0xd0, 0x36, 0x2f, 0x2a,
+			0x2d, 0x2d, 0x0a, 0x90, 0xcf, 0x1a, 0x5a, 0x4c,
+			0x5d, 0xb0, 0x2d, 0x56, 0xec, 0xc4, 0xc5, 0xbf,
+			0x34, 0x00, 0x72, 0x08, 0xd5, 0xb8, 0x87, 0x18,
+			0x58, 0x65,
+		},
+	},
+	{
+		sha256.New,
+		[]byte{
+			0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+			0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+			0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+			0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
+			0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
+			0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+			0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
+			0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
+			0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+		},
+		[]byte{
+			0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
+			0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+			0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
+			0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
+			0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
+			0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
+			0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
+			0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
+			0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
+			0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
+		},
+		[]byte{
+			0x06, 0xa6, 0xb8, 0x8c, 0x58, 0x53, 0x36, 0x1a,
+			0x06, 0x10, 0x4c, 0x9c, 0xeb, 0x35, 0xb4, 0x5c,
+			0xef, 0x76, 0x00, 0x14, 0x90, 0x46, 0x71, 0x01,
+			0x4a, 0x19, 0x3f, 0x40, 0xc1, 0x5f, 0xc2, 0x44,
+		},
+		[]byte{
+			0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
+			0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
+			0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
+			0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
+			0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
+			0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
+			0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
+			0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
+			0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+			0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
+		},
+		[]byte{
+			0xb1, 0x1e, 0x39, 0x8d, 0xc8, 0x03, 0x27, 0xa1,
+			0xc8, 0xe7, 0xf7, 0x8c, 0x59, 0x6a, 0x49, 0x34,
+			0x4f, 0x01, 0x2e, 0xda, 0x2d, 0x4e, 0xfa, 0xd8,
+			0xa0, 0x50, 0xcc, 0x4c, 0x19, 0xaf, 0xa9, 0x7c,
+			0x59, 0x04, 0x5a, 0x99, 0xca, 0xc7, 0x82, 0x72,
+			0x71, 0xcb, 0x41, 0xc6, 0x5e, 0x59, 0x0e, 0x09,
+			0xda, 0x32, 0x75, 0x60, 0x0c, 0x2f, 0x09, 0xb8,
+			0x36, 0x77, 0x93, 0xa9, 0xac, 0xa3, 0xdb, 0x71,
+			0xcc, 0x30, 0xc5, 0x81, 0x79, 0xec, 0x3e, 0x87,
+			0xc1, 0x4c, 0x01, 0xd5, 0xc1, 0xf3, 0x43, 0x4f,
+			0x1d, 0x87,
+		},
+	},
+	{
+		sha256.New,
+		[]byte{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+		},
+		[]byte{},
+		[]byte{
+			0x19, 0xef, 0x24, 0xa3, 0x2c, 0x71, 0x7b, 0x16,
+			0x7f, 0x33, 0xa9, 0x1d, 0x6f, 0x64, 0x8b, 0xdf,
+			0x96, 0x59, 0x67, 0x76, 0xaf, 0xdb, 0x63, 0x77,
+			0xac, 0x43, 0x4c, 0x1c, 0x29, 0x3c, 0xcb, 0x04,
+		},
+		[]byte{},
+		[]byte{
+			0x8d, 0xa4, 0xe7, 0x75, 0xa5, 0x63, 0xc1, 0x8f,
+			0x71, 0x5f, 0x80, 0x2a, 0x06, 0x3c, 0x5a, 0x31,
+			0xb8, 0xa1, 0x1f, 0x5c, 0x5e, 0xe1, 0x87, 0x9e,
+			0xc3, 0x45, 0x4e, 0x5f, 0x3c, 0x73, 0x8d, 0x2d,
+			0x9d, 0x20, 0x13, 0x95, 0xfa, 0xa4, 0xb6, 0x1a,
+			0x96, 0xc8,
+		},
+	},
+	{
+		sha256.New,
+		[]byte{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+		},
+		nil,
+		[]byte{
+			0x19, 0xef, 0x24, 0xa3, 0x2c, 0x71, 0x7b, 0x16,
+			0x7f, 0x33, 0xa9, 0x1d, 0x6f, 0x64, 0x8b, 0xdf,
+			0x96, 0x59, 0x67, 0x76, 0xaf, 0xdb, 0x63, 0x77,
+			0xac, 0x43, 0x4c, 0x1c, 0x29, 0x3c, 0xcb, 0x04,
+		},
+		nil,
+		[]byte{
+			0x8d, 0xa4, 0xe7, 0x75, 0xa5, 0x63, 0xc1, 0x8f,
+			0x71, 0x5f, 0x80, 0x2a, 0x06, 0x3c, 0x5a, 0x31,
+			0xb8, 0xa1, 0x1f, 0x5c, 0x5e, 0xe1, 0x87, 0x9e,
+			0xc3, 0x45, 0x4e, 0x5f, 0x3c, 0x73, 0x8d, 0x2d,
+			0x9d, 0x20, 0x13, 0x95, 0xfa, 0xa4, 0xb6, 0x1a,
+			0x96, 0xc8,
+		},
+	},
+	{
+		sha1.New,
+		[]byte{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b,
+		},
+		[]byte{
+			0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			0x08, 0x09, 0x0a, 0x0b, 0x0c,
+		},
+		[]byte{
+			0x9b, 0x6c, 0x18, 0xc4, 0x32, 0xa7, 0xbf, 0x8f,
+			0x0e, 0x71, 0xc8, 0xeb, 0x88, 0xf4, 0xb3, 0x0b,
+			0xaa, 0x2b, 0xa2, 0x43,
+		},
+		[]byte{
+			0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+			0xf8, 0xf9,
+		},
+		[]byte{
+			0x08, 0x5a, 0x01, 0xea, 0x1b, 0x10, 0xf3, 0x69,
+			0x33, 0x06, 0x8b, 0x56, 0xef, 0xa5, 0xad, 0x81,
+			0xa4, 0xf1, 0x4b, 0x82, 0x2f, 0x5b, 0x09, 0x15,
+			0x68, 0xa9, 0xcd, 0xd4, 0xf1, 0x55, 0xfd, 0xa2,
+			0xc2, 0x2e, 0x42, 0x24, 0x78, 0xd3, 0x05, 0xf3,
+			0xf8, 0x96,
+		},
+	},
+	{
+		sha1.New,
+		[]byte{
+			0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+			0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+			0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+			0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
+			0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
+			0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+			0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
+			0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
+			0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+		},
+		[]byte{
+			0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
+			0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+			0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
+			0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
+			0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
+			0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
+			0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
+			0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
+			0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
+			0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
+		},
+		[]byte{
+			0x8a, 0xda, 0xe0, 0x9a, 0x2a, 0x30, 0x70, 0x59,
+			0x47, 0x8d, 0x30, 0x9b, 0x26, 0xc4, 0x11, 0x5a,
+			0x22, 0x4c, 0xfa, 0xf6,
+		},
+		[]byte{
+			0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
+			0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
+			0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
+			0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
+			0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
+			0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
+			0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
+			0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
+			0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+			0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
+		},
+		[]byte{
+			0x0b, 0xd7, 0x70, 0xa7, 0x4d, 0x11, 0x60, 0xf7,
+			0xc9, 0xf1, 0x2c, 0xd5, 0x91, 0x2a, 0x06, 0xeb,
+			0xff, 0x6a, 0xdc, 0xae, 0x89, 0x9d, 0x92, 0x19,
+			0x1f, 0xe4, 0x30, 0x56, 0x73, 0xba, 0x2f, 0xfe,
+			0x8f, 0xa3, 0xf1, 0xa4, 0xe5, 0xad, 0x79, 0xf3,
+			0xf3, 0x34, 0xb3, 0xb2, 0x02, 0xb2, 0x17, 0x3c,
+			0x48, 0x6e, 0xa3, 0x7c, 0xe3, 0xd3, 0x97, 0xed,
+			0x03, 0x4c, 0x7f, 0x9d, 0xfe, 0xb1, 0x5c, 0x5e,
+			0x92, 0x73, 0x36, 0xd0, 0x44, 0x1f, 0x4c, 0x43,
+			0x00, 0xe2, 0xcf, 0xf0, 0xd0, 0x90, 0x0b, 0x52,
+			0xd3, 0xb4,
+		},
+	},
+	{
+		sha1.New,
+		[]byte{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+		},
+		[]byte{},
+		[]byte{
+			0xda, 0x8c, 0x8a, 0x73, 0xc7, 0xfa, 0x77, 0x28,
+			0x8e, 0xc6, 0xf5, 0xe7, 0xc2, 0x97, 0x78, 0x6a,
+			0xa0, 0xd3, 0x2d, 0x01,
+		},
+		[]byte{},
+		[]byte{
+			0x0a, 0xc1, 0xaf, 0x70, 0x02, 0xb3, 0xd7, 0x61,
+			0xd1, 0xe5, 0x52, 0x98, 0xda, 0x9d, 0x05, 0x06,
+			0xb9, 0xae, 0x52, 0x05, 0x72, 0x20, 0xa3, 0x06,
+			0xe0, 0x7b, 0x6b, 0x87, 0xe8, 0xdf, 0x21, 0xd0,
+			0xea, 0x00, 0x03, 0x3d, 0xe0, 0x39, 0x84, 0xd3,
+			0x49, 0x18,
+		},
+	},
+	{
+		sha1.New,
+		[]byte{
+			0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c,
+			0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c,
+			0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c,
+		},
+		nil,
+		[]byte{
+			0x2a, 0xdc, 0xca, 0xda, 0x18, 0x77, 0x9e, 0x7c,
+			0x20, 0x77, 0xad, 0x2e, 0xb1, 0x9d, 0x3f, 0x3e,
+			0x73, 0x13, 0x85, 0xdd,
+		},
+		nil,
+		[]byte{
+			0x2c, 0x91, 0x11, 0x72, 0x04, 0xd7, 0x45, 0xf3,
+			0x50, 0x0d, 0x63, 0x6a, 0x62, 0xf6, 0x4f, 0x0a,
+			0xb3, 0xba, 0xe5, 0x48, 0xaa, 0x53, 0xd4, 0x23,
+			0xb0, 0xd1, 0xf2, 0x7e, 0xbb, 0xa6, 0xf5, 0xe5,
+			0x67, 0x3a, 0x08, 0x1d, 0x70, 0xcc, 0xe7, 0xac,
+			0xfc, 0x48,
+		},
+	},
+}
+
+func TestHKDF(t *testing.T) {
+	for i, tt := range hkdfTests {
+		prk := Extract(tt.hash, tt.master, tt.salt)
+		if !bytes.Equal(prk, tt.prk) {
+			t.Errorf("test %d: incorrect PRK: have %v, need %v.", i, prk, tt.prk)
+		}
+
+		hkdf := New(tt.hash, tt.master, tt.salt, tt.info)
+		out := make([]byte, len(tt.out))
+
+		n, err := io.ReadFull(hkdf, out)
+		if n != len(tt.out) || err != nil {
+			t.Errorf("test %d: not enough output bytes: %d.", i, n)
+		}
+
+		if !bytes.Equal(out, tt.out) {
+			t.Errorf("test %d: incorrect output: have %v, need %v.", i, out, tt.out)
+		}
+
+		hkdf = Expand(tt.hash, prk, tt.info)
+
+		n, err = io.ReadFull(hkdf, out)
+		if n != len(tt.out) || err != nil {
+			t.Errorf("test %d: not enough output bytes from Expand: %d.", i, n)
+		}
+
+		if !bytes.Equal(out, tt.out) {
+			t.Errorf("test %d: incorrect output from Expand: have %v, need %v.", i, out, tt.out)
+		}
+	}
+}
+
+func TestHKDFMultiRead(t *testing.T) {
+	for i, tt := range hkdfTests {
+		hkdf := New(tt.hash, tt.master, tt.salt, tt.info)
+		out := make([]byte, len(tt.out))
+
+		for b := 0; b < len(tt.out); b++ {
+			n, err := io.ReadFull(hkdf, out[b:b+1])
+			if n != 1 || err != nil {
+				t.Errorf("test %d.%d: not enough output bytes: have %d, need %d .", i, b, n, len(tt.out))
+			}
+		}
+
+		if !bytes.Equal(out, tt.out) {
+			t.Errorf("test %d: incorrect output: have %v, need %v.", i, out, tt.out)
+		}
+	}
+}
+
+func TestHKDFLimit(t *testing.T) {
+	hash := sha1.New
+	master := []byte{0x00, 0x01, 0x02, 0x03}
+	info := []byte{}
+
+	hkdf := New(hash, master, nil, info)
+	limit := hash().Size() * 255
+	out := make([]byte, limit)
+
+	// The maximum output bytes should be extractable
+	n, err := io.ReadFull(hkdf, out)
+	if n != limit || err != nil {
+		t.Errorf("not enough output bytes: %d, %v.", n, err)
+	}
+
+	// Reading one more should fail
+	n, err = io.ReadFull(hkdf, make([]byte, 1))
+	if n > 0 || err == nil {
+		t.Errorf("key expansion overflowed: n = %d, err = %v", n, err)
+	}
+}
+
+func Benchmark16ByteMD5Single(b *testing.B) {
+	benchmarkHKDFSingle(md5.New, 16, b)
+}
+
+func Benchmark20ByteSHA1Single(b *testing.B) {
+	benchmarkHKDFSingle(sha1.New, 20, b)
+}
+
+func Benchmark32ByteSHA256Single(b *testing.B) {
+	benchmarkHKDFSingle(sha256.New, 32, b)
+}
+
+func Benchmark64ByteSHA512Single(b *testing.B) {
+	benchmarkHKDFSingle(sha512.New, 64, b)
+}
+
+func Benchmark8ByteMD5Stream(b *testing.B) {
+	benchmarkHKDFStream(md5.New, 8, b)
+}
+
+func Benchmark16ByteMD5Stream(b *testing.B) {
+	benchmarkHKDFStream(md5.New, 16, b)
+}
+
+func Benchmark8ByteSHA1Stream(b *testing.B) {
+	benchmarkHKDFStream(sha1.New, 8, b)
+}
+
+func Benchmark20ByteSHA1Stream(b *testing.B) {
+	benchmarkHKDFStream(sha1.New, 20, b)
+}
+
+func Benchmark8ByteSHA256Stream(b *testing.B) {
+	benchmarkHKDFStream(sha256.New, 8, b)
+}
+
+func Benchmark32ByteSHA256Stream(b *testing.B) {
+	benchmarkHKDFStream(sha256.New, 32, b)
+}
+
+func Benchmark8ByteSHA512Stream(b *testing.B) {
+	benchmarkHKDFStream(sha512.New, 8, b)
+}
+
+func Benchmark64ByteSHA512Stream(b *testing.B) {
+	benchmarkHKDFStream(sha512.New, 64, b)
+}
+
+func benchmarkHKDFSingle(hasher func() hash.Hash, block int, b *testing.B) {
+	master := []byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07}
+	salt := []byte{0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17}
+	info := []byte{0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27}
+	out := make([]byte, block)
+
+	b.SetBytes(int64(block))
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		hkdf := New(hasher, master, salt, info)
+		io.ReadFull(hkdf, out)
+	}
+}
+
+func benchmarkHKDFStream(hasher func() hash.Hash, block int, b *testing.B) {
+	master := []byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07}
+	salt := []byte{0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17}
+	info := []byte{0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27}
+	out := make([]byte, block)
+
+	b.SetBytes(int64(block))
+	b.ResetTimer()
+
+	hkdf := New(hasher, master, salt, info)
+	for i := 0; i < b.N; i++ {
+		_, err := io.ReadFull(hkdf, out)
+		if err != nil {
+			hkdf = New(hasher, master, salt, info)
+			i--
+		}
+	}
+}