Add session ticket padding

psiphon/common/tls/obfuscated.go

@@ -21,6 +21,7 @@ package tls
 
 import (
 	"crypto/rand"
+	"math/big"
 )
 
 // [Psiphon]
@@ -94,11 +95,19 @@ func (cache *obfuscatedClientSessionCache) Get(key string) (*ClientSessionState,
 
 func newObfuscatedClientSessionState(sharedSecret [32]byte) (*ClientSessionState, error) {
 
+	// Pad golang TLS session ticket to a more typical size.
+	paddingSize := 72
+	randomInt, err := rand.Int(rand.Reader, big.NewInt(18))
+	if err != nil {
+		return nil, err
+	}
+	paddingSize += int(randomInt.Int64()) * 2
+
 	// Create a session ticket that wasn't actually issued by the server.
 	vers := uint16(VersionTLS12)
 	cipherSuite := TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
 	masterSecret := make([]byte, masterSecretLength)
-	_, err := rand.Read(masterSecret)
+	_, err = rand.Read(masterSecret)
 	if err != nil {
 		return nil, err
 	}
@@ -107,6 +116,7 @@ func newObfuscatedClientSessionState(sharedSecret [32]byte) (*ClientSessionState
 		cipherSuite:  cipherSuite,
 		masterSecret: masterSecret,
 		certificates: nil,
+		paddingSize:  paddingSize,
 	}
 	c := &Conn{
 		config: &Config{

psiphon/common/tls/ticket.go

@@ -25,6 +25,10 @@ type sessionState struct {
 	// usedOldKey is true if the ticket from which this session came from
 	// was encrypted with an older key and thus should be refreshed.
 	usedOldKey bool
+
+	// [Psiphon]
+	// Padding for obfuscated session tickets
+	paddingSize int
 }
 
 func (s *sessionState) equal(i interface{}) bool {
@@ -58,6 +62,10 @@ func (s *sessionState) marshal() []byte {
 		length += 4 + len(cert)
 	}
 
+	// [Psiphon]
+	// Add padding for obfuscated session tickets
+	length += s.paddingSize
+
 	ret := make([]byte, length)
 	x := ret
 	x[0] = byte(s.vers >> 8)
@@ -126,7 +134,11 @@ func (s *sessionState) unmarshal(data []byte) bool {
 		data = data[certLen:]
 	}
 
-	return len(data) == 0
+	// [Psiphon]
+	// Ignore padding for obfuscated session tickets
+	//return len(data) == 0
+	return true
+
 }
 
 func (c *Conn) encryptTicket(state *sessionState) ([]byte, error) {