crypto/tls: don't rely on map iteration order.

Previously we were using the map iteration order to set the order of
the cipher suites in the ClientHello.

R=bradfitz
CC=golang-dev
https://golang.org/cl/5440048

src/pkg/crypto/tls/cipher_suites.go

@@ -37,6 +37,7 @@ type keyAgreement interface {
 // A cipherSuite is a specific combination of key agreement, cipher and MAC
 // function. All cipher suites currently assume RSA key agreement.
 type cipherSuite struct {
+	id uint16
 	// the lengths, in bytes, of the key material needed for each component.
 	keyLen int
 	macLen int
@@ -50,13 +51,13 @@ type cipherSuite struct {
 	mac      func(version uint16, macKey []byte) macFunction
 }
 
-var cipherSuites = map[uint16]*cipherSuite{
-	TLS_RSA_WITH_RC4_128_SHA:            &cipherSuite{16, 20, 0, rsaKA, false, cipherRC4, macSHA1},
-	TLS_RSA_WITH_3DES_EDE_CBC_SHA:       &cipherSuite{24, 20, 8, rsaKA, false, cipher3DES, macSHA1},
-	TLS_RSA_WITH_AES_128_CBC_SHA:        &cipherSuite{16, 20, 16, rsaKA, false, cipherAES, macSHA1},
-	TLS_ECDHE_RSA_WITH_RC4_128_SHA:      &cipherSuite{16, 20, 0, ecdheRSAKA, true, cipherRC4, macSHA1},
-	TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA: &cipherSuite{24, 20, 8, ecdheRSAKA, true, cipher3DES, macSHA1},
-	TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA:  &cipherSuite{16, 20, 16, ecdheRSAKA, true, cipherAES, macSHA1},
+var cipherSuites = []*cipherSuite{
+	&cipherSuite{TLS_RSA_WITH_RC4_128_SHA, 16, 20, 0, rsaKA, false, cipherRC4, macSHA1},
+	&cipherSuite{TLS_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, rsaKA, false, cipher3DES, macSHA1},
+	&cipherSuite{TLS_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, rsaKA, false, cipherAES, macSHA1},
+	&cipherSuite{TLS_ECDHE_RSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheRSAKA, true, cipherRC4, macSHA1},
+	&cipherSuite{TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, ecdheRSAKA, true, cipher3DES, macSHA1},
+	&cipherSuite{TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, ecdheRSAKA, true, cipherAES, macSHA1},
 }
 
 func cipherRC4(key, iv []byte, isRead bool) interface{} {
@@ -159,15 +160,20 @@ func ecdheRSAKA() keyAgreement {
 	return new(ecdheRSAKeyAgreement)
 }
 
-// mutualCipherSuite returns a cipherSuite and its id given a list of supported
+// mutualCipherSuite returns a cipherSuite given a list of supported
 // ciphersuites and the id requested by the peer.
-func mutualCipherSuite(have []uint16, want uint16) (suite *cipherSuite, id uint16) {
+func mutualCipherSuite(have []uint16, want uint16) *cipherSuite {
 	for _, id := range have {
 		if id == want {
-			return cipherSuites[id], id
+			for _, suite := range cipherSuites {
+				if suite.id == want {
+					return suite
+				}
+			}
+			return nil
 		}
 	}
-	return
+	return nil
 }
 
 // A list of the possible cipher suite ids. Taken from

src/pkg/crypto/tls/common.go

@@ -315,9 +315,7 @@ var (
 
 func initDefaultCipherSuites() {
 	varDefaultCipherSuites = make([]uint16, len(cipherSuites))
-	i := 0
-	for id := range cipherSuites {
-		varDefaultCipherSuites[i] = id
-		i++
+	for i, suite := range cipherSuites {
+		varDefaultCipherSuites[i] = suite.id
 	}
 }

src/pkg/crypto/tls/handshake_client.go

@@ -72,7 +72,7 @@ func (c *Conn) clientHandshake() error {
 		return errors.New("server advertised unrequested NPN")
 	}
 
-	suite, suiteId := mutualCipherSuite(c.config.cipherSuites(), serverHello.cipherSuite)
+	suite := mutualCipherSuite(c.config.cipherSuites(), serverHello.cipherSuite)
 	if suite == nil {
 		return c.sendAlert(alertHandshakeFailure)
 	}
@@ -292,7 +292,7 @@ func (c *Conn) clientHandshake() error {
 	}
 
 	c.handshakeComplete = true
-	c.cipherSuite = suiteId
+	c.cipherSuite = suite.id
 	return nil
 }
 

src/pkg/crypto/tls/handshake_server.go

@@ -56,18 +56,25 @@ Curves:
 	ellipticOk := supportedCurve && supportedPointFormat
 
 	var suite *cipherSuite
-	var suiteId uint16
 FindCipherSuite:
 	for _, id := range clientHello.cipherSuites {
 		for _, supported := range config.cipherSuites() {
 			if id == supported {
-				suite = cipherSuites[id]
+				suite = nil
+				for _, s := range cipherSuites {
+					if s.id == id {
+						suite = s
+						break
+					}
+				}
+				if suite == nil {
+					continue
+				}
 				// Don't select a ciphersuite which we can't
 				// support for this client.
 				if suite.elliptic && !ellipticOk {
 					continue
 				}
-				suiteId = id
 				break FindCipherSuite
 			}
 		}
@@ -87,7 +94,7 @@ FindCipherSuite:
 	}
 
 	hello.vers = vers
-	hello.cipherSuite = suiteId
+	hello.cipherSuite = suite.id
 	t := uint32(config.time())
 	hello.random = make([]byte, 32)
 	hello.random[0] = byte(t >> 24)
@@ -296,7 +303,7 @@ FindCipherSuite:
 	c.writeRecord(recordTypeHandshake, finished.marshal())
 
 	c.handshakeComplete = true
-	c.cipherSuite = suiteId
+	c.cipherSuite = suite.id
 
 	return nil
 }