go.crypto/hkdf: implement hash-based, key derivation.

Detailed description in RFC 5869.

LGTM=agl
R=agl, minux.ma
CC=golang-codereviews
https://golang.org/cl/7474049

hkdf/example_test.go

@@ -0,0 +1,61 @@
+// 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"
+	"code.google.com/p/go.crypto/hkdf"
+	"crypto/rand"
+	"crypto/sha256"
+	"fmt"
+	"io"
+)
+
+// Usage example that expands one master key into three other cryptographically
+// secure keys.
+func Example_usage() {
+	// Underlying hash function to use
+	hash := sha256.New
+
+	// Cryptographically secure master key.
+	master := []byte{0x00, 0x01, 0x02, 0x03} // i.e. NOT this.
+
+	// Non secret salt, optional (can be nil)
+	// Recommended: hash-length sized random
+	salt := make([]byte, hash().Size())
+	n, err := io.ReadFull(rand.Reader, salt)
+	if n != len(salt) || err != nil {
+		fmt.Println("error:", err)
+		return
+	}
+
+	// Non secret context specific info, optional (can be nil).
+	// Note, independent from the master key.
+	info := []byte{0x03, 0x14, 0x15, 0x92, 0x65}
+
+	// Create the key derivation function
+	hkdf := hkdf.New(hash, master, salt, info)
+
+	// Generate the required keys
+	keys := make([][]byte, 3)
+	for i := 0; i < len(keys); i++ {
+		keys[i] = make([]byte, 24)
+		n, err := io.ReadFull(hkdf, keys[i])
+		if n != len(keys[i]) || err != nil {
+			fmt.Println("error:", err)
+			return
+		}
+	}
+
+	// Keys should contain 192 bit random keys
+	for i := 1; i <= len(keys); i++ {
+		fmt.Printf("Key #%d: %v\n", i, !bytes.Equal(keys[i-1], make([]byte, 24)))
+	}
+
+	// Output:
+	// Key #1: true
+	// Key #2: true
+	// Key #3: true
+}

hkdf/hkdf.go

@@ -0,0 +1,77 @@
+// 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.
+//
+// RFC 5869: https://tools.ietf.org/html/rfc5869
+package hkdf
+
+import (
+	"crypto/hmac"
+	"errors"
+	"hash"
+	"io"
+)
+
+type hkdf struct {
+	expander hash.Hash
+	size     int
+
+	info    []byte
+	counter byte
+
+	prev  []byte
+	cache []byte
+}
+
+func (f *hkdf) Read(p []byte) (int, error) {
+	// Check whether enough data can be generated
+	need := len(p)
+	remains := len(f.cache) + int(255-f.counter+1)*f.size
+	if remains < need {
+		return 0, errors.New("hkdf: entropy limit reached")
+	}
+	// Read from the cache, if enough data is present
+	n := copy(p, f.cache)
+	p = p[n:]
+
+	// Fill the buffer
+	var input []byte
+	for len(p) > 0 {
+		input = append(f.prev, f.info...)
+		input = append(input, f.counter)
+
+		f.expander.Reset()
+		f.expander.Write(input)
+		f.prev = f.expander.Sum(f.prev[:0])
+		f.counter++
+
+		// Copy the new batch into p
+		f.cache = f.prev
+		n = copy(p, f.cache)
+		p = p[n:]
+	}
+	// Save leftovers for next run
+	f.cache = f.cache[n:]
+
+	return need, nil
+}
+
+// New returns a new HKDF using the given hash, the secret keying material to expand
+// and optional salt and info fields.
+func New(hash func() hash.Hash, secret, salt, info []byte) io.Reader {
+	if salt == nil {
+		salt = make([]byte, hash().Size())
+	}
+	extractor := hmac.New(hash, salt)
+	extractor.Write(secret)
+	prk := extractor.Sum(nil)
+
+	return &hkdf{hmac.New(hash, prk), extractor.Size(), info, 1, nil, nil}
+}

hkdf/hkdf_test.go

@@ -0,0 +1,370 @@
+// 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
+	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{
+			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{
+			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{},
+		[]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{
+			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{
+			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{},
+		[]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{},
+		[]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 {
+		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)
+		}
+	}
+}
+
+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--
+		}
+	}
+}