crypto/hmac: make Sum idempotent

Fixes #978.

R=rsc
CC=golang-dev
https://golang.org/cl/1967045

src/pkg/crypto/hmac/hmac.go

@@ -34,10 +34,9 @@ const (
 )
 
 type hmac struct {
-	size  int
-	key   []byte
-	tmp   []byte
-	inner hash.Hash
+	size         int
+	key, tmp     []byte
+	outer, inner hash.Hash
 }
 
 func (h *hmac) tmpPad(xor byte) {
@@ -50,14 +49,14 @@ func (h *hmac) tmpPad(xor byte) {
 }
 
 func (h *hmac) Sum() []byte {
-	h.tmpPad(0x5c)
 	sum := h.inner.Sum()
+	h.tmpPad(0x5c)
 	for i, b := range sum {
 		h.tmp[padSize+i] = b
 	}
-	h.inner.Reset()
-	h.inner.Write(h.tmp)
-	return h.inner.Sum()
+	h.outer.Reset()
+	h.outer.Write(h.tmp)
+	return h.outer.Sum()
 }
 
 func (h *hmac) Write(p []byte) (n int, err os.Error) {
@@ -72,27 +71,26 @@ func (h *hmac) Reset() {
 	h.inner.Write(h.tmp[0:padSize])
 }
 
-// New returns a new HMAC hash using the given hash and key.
-func New(h hash.Hash, key []byte) hash.Hash {
+// New returns a new HMAC hash using the given hash generator and key.
+func New(h func() hash.Hash, key []byte) hash.Hash {
+	hm := new(hmac)
+	hm.outer = h()
+	hm.inner = h()
+	hm.size = hm.inner.Size()
+	hm.tmp = make([]byte, padSize+hm.size)
 	if len(key) > padSize {
 		// If key is too big, hash it.
-		h.Write(key)
-		key = h.Sum()
+		hm.outer.Write(key)
+		key = hm.outer.Sum()
 	}
-	hm := new(hmac)
-	hm.inner = h
-	hm.size = h.Size()
 	hm.key = make([]byte, len(key))
-	for i, k := range key {
-		hm.key[i] = k
-	}
-	hm.tmp = make([]byte, padSize+hm.size)
+	copy(hm.key, key)
 	hm.Reset()
 	return hm
 }
 
 // NewMD5 returns a new HMAC-MD5 hash using the given key.
-func NewMD5(key []byte) hash.Hash { return New(md5.New(), key) }
+func NewMD5(key []byte) hash.Hash { return New(md5.New, key) }
 
 // NewSHA1 returns a new HMAC-SHA1 hash using the given key.
-func NewSHA1(key []byte) hash.Hash { return New(sha1.New(), key) }
+func NewSHA1(key []byte) hash.Hash { return New(sha1.New, key) }

src/pkg/crypto/hmac/hmac_test.go

@@ -84,9 +84,13 @@ func TestHMAC(t *testing.T) {
 				t.Errorf("test %d.%d: Write(%d) = %d, %v", i, j, len(tt.in), n, err)
 				continue
 			}
-			sum := fmt.Sprintf("%x", h.Sum())
-			if sum != tt.out {
-				t.Errorf("test %d.%d: have %s want %s\n", i, j, sum, tt.out)
+
+			// Repetive Sum() calls should return the same value
+			for k := 0; k < 2; k++ {
+				sum := fmt.Sprintf("%x", h.Sum())
+				if sum != tt.out {
+					t.Errorf("test %d.%d.%d: have %s want %s\n", i, j, k, sum, tt.out)
+				}
 			}
 
 			// Second iteration: make sure reset works.

src/pkg/crypto/tls/handshake_client.go

@@ -8,7 +8,6 @@ import (
 	"crypto/hmac"
 	"crypto/rc4"
 	"crypto/rsa"
-	"crypto/sha1"
 	"crypto/subtle"
 	"crypto/x509"
 	"io"
@@ -226,7 +225,7 @@ func (c *Conn) clientHandshake() os.Error {
 
 	cipher, _ := rc4.NewCipher(clientKey)
 
-	c.out.prepareCipherSpec(cipher, hmac.New(sha1.New(), clientMAC))
+	c.out.prepareCipherSpec(cipher, hmac.NewSHA1(clientMAC))
 	c.writeRecord(recordTypeChangeCipherSpec, []byte{1})
 
 	finished := new(finishedMsg)
@@ -235,7 +234,7 @@ func (c *Conn) clientHandshake() os.Error {
 	c.writeRecord(recordTypeHandshake, finished.marshal())
 
 	cipher2, _ := rc4.NewCipher(serverKey)
-	c.in.prepareCipherSpec(cipher2, hmac.New(sha1.New(), serverMAC))
+	c.in.prepareCipherSpec(cipher2, hmac.NewSHA1(serverMAC))
 	c.readRecord(recordTypeChangeCipherSpec)
 	if c.err != nil {
 		return c.err

src/pkg/crypto/tls/handshake_server.go

@@ -16,7 +16,6 @@ import (
 	"crypto/hmac"
 	"crypto/rc4"
 	"crypto/rsa"
-	"crypto/sha1"
 	"crypto/subtle"
 	"crypto/x509"
 	"io"
@@ -227,7 +226,7 @@ func (c *Conn) serverHandshake() os.Error {
 		keysFromPreMasterSecret11(preMasterSecret, clientHello.random, hello.random, suite.hashLength, suite.cipherKeyLength)
 
 	cipher, _ := rc4.NewCipher(clientKey)
-	c.in.prepareCipherSpec(cipher, hmac.New(sha1.New(), clientMAC))
+	c.in.prepareCipherSpec(cipher, hmac.NewSHA1(clientMAC))
 	c.readRecord(recordTypeChangeCipherSpec)
 	if err := c.error(); err != nil {
 		return err
@@ -264,7 +263,7 @@ func (c *Conn) serverHandshake() os.Error {
 	finishedHash.Write(clientFinished.marshal())
 
 	cipher2, _ := rc4.NewCipher(serverKey)
-	c.out.prepareCipherSpec(cipher2, hmac.New(sha1.New(), serverMAC))
+	c.out.prepareCipherSpec(cipher2, hmac.NewSHA1(serverMAC))
 	c.writeRecord(recordTypeChangeCipherSpec, []byte{1})
 
 	finished := new(finishedMsg)

src/pkg/crypto/tls/prf.go

@@ -20,7 +20,7 @@ func splitPreMasterSecret(secret []byte) (s1, s2 []byte) {
 }
 
 // pHash implements the P_hash function, as defined in RFC 4346, section 5.
-func pHash(result, secret, seed []byte, hash hash.Hash) {
+func pHash(result, secret, seed []byte, hash func() hash.Hash) {
 	h := hmac.New(hash, secret)
 	h.Write(seed)
 	a := h.Sum()
@@ -46,8 +46,8 @@ func pHash(result, secret, seed []byte, hash hash.Hash) {
 
 // pRF11 implements the TLS 1.1 pseudo-random function, as defined in RFC 4346, section 5.
 func pRF11(result, secret, label, seed []byte) {
-	hashSHA1 := sha1.New()
-	hashMD5 := md5.New()
+	hashSHA1 := sha1.New
+	hashMD5 := md5.New
 
 	labelAndSeed := make([]byte, len(label)+len(seed))
 	copy(labelAndSeed, label)