diff --git a/src/pkg/crypto/tls/ca_set.go b/src/pkg/crypto/tls/ca_set.go
index fe2a540f4db..ae00ac55868 100644
--- a/src/pkg/crypto/tls/ca_set.go
+++ b/src/pkg/crypto/tls/ca_set.go
@@ -16,6 +16,7 @@ type CASet struct {
 	byName         map[string][]*x509.Certificate
 }
 
+// NewCASet returns a new, empty CASet.
 func NewCASet() *CASet {
 	return &CASet{
 		make(map[string][]*x509.Certificate),
diff --git a/src/pkg/crypto/tls/common.go b/src/pkg/crypto/tls/common.go
index a4f2b804f10..4fb17ad3a89 100644
--- a/src/pkg/crypto/tls/common.go
+++ b/src/pkg/crypto/tls/common.go
@@ -78,6 +78,7 @@ const (
 	// Rest of these are reserved by the TLS spec
 )
 
+// ConnectionState records basic TLS details about the connection.
 type ConnectionState struct {
 	HandshakeComplete  bool
 	CipherSuite        uint16
@@ -88,28 +89,65 @@ type ConnectionState struct {
 // has been passed to a TLS function it must not be modified.
 type Config struct {
 	// Rand provides the source of entropy for nonces and RSA blinding.
+	// If Rand is nil, TLS uses the cryptographic random reader in package
+	// crypto/rand.
 	Rand io.Reader
+
 	// Time returns the current time as the number of seconds since the epoch.
+	// If Time is nil, TLS uses the system time.Seconds.
 	Time func() int64
-	// Certificates contains one or more certificate chains.
+
+	// Certificates contains one or more certificate chains
+	// to present to the other side of the connection.
+	// Server configurations must include at least one certificate.
 	Certificates []Certificate
-	RootCAs      *CASet
+
+	// RootCAs defines the set of root certificate authorities
+	// that clients use when verifying server certificates.
+	// If RootCAs is nil, TLS uses the host's root CA set.
+	RootCAs *CASet
+
 	// NextProtos is a list of supported, application level protocols.
 	// Currently only server-side handling is supported.
 	NextProtos []string
+
 	// ServerName is included in the client's handshake to support virtual
 	// hosting.
 	ServerName string
-	// AuthenticateClient determines if a server will request a certificate
+
+	// AuthenticateClient controls whether a server will request a certificate
 	// from the client. It does not require that the client send a
-	// certificate nor, if it does, that the certificate is anything more
-	// than self-signed.
+	// certificate nor does it require that the certificate sent be
+	// anything more than self-signed.
 	AuthenticateClient bool
 }
 
+func (c *Config) rand() io.Reader {
+	r := c.Rand
+	if r == nil {
+		return rand.Reader
+	}
+	return r
+}
+
+func (c *Config) time() int64 {
+	t := c.Time
+	if t == nil {
+		t = time.Seconds
+	}
+	return t()
+}
+
+func (c *Config) rootCAs() *CASet {
+	s := c.RootCAs
+	if s == nil {
+		s = defaultRoots()
+	}
+	return s
+}
+
+// A Certificate is a chain of one or more certificates, leaf first.
 type Certificate struct {
-	// Certificate contains a chain of one or more certificates. Leaf
-	// certificate first.
 	Certificate [][]byte
 	PrivateKey  *rsa.PrivateKey
 }
@@ -143,14 +181,10 @@ func mutualVersion(vers uint16) (uint16, bool) {
 	return vers, true
 }
 
-// The defaultConfig is used in place of a nil *Config in the TLS server and client.
-var varDefaultConfig *Config
-
-var once sync.Once
+var emptyConfig Config
 
 func defaultConfig() *Config {
-	once.Do(initDefaultConfig)
-	return varDefaultConfig
+	return &emptyConfig
 }
 
 // Possible certificate files; stop after finding one.
@@ -162,7 +196,16 @@ var certFiles = []string{
 	"/usr/share/curl/curl-ca-bundle.crt", // OS X
 }
 
-func initDefaultConfig() {
+var once sync.Once
+
+func defaultRoots() *CASet {
+	once.Do(initDefaultRoots)
+	return varDefaultRoots
+}
+
+var varDefaultRoots *CASet
+
+func initDefaultRoots() {
 	roots := NewCASet()
 	for _, file := range certFiles {
 		data, err := ioutil.ReadFile(file)
@@ -171,10 +214,5 @@ func initDefaultConfig() {
 			break
 		}
 	}
-
-	varDefaultConfig = &Config{
-		Rand:    rand.Reader,
-		Time:    time.Seconds,
-		RootCAs: roots,
-	}
+	varDefaultRoots = roots
 }
diff --git a/src/pkg/crypto/tls/handshake_client.go b/src/pkg/crypto/tls/handshake_client.go
index b6b0e0fad37..4cddba33030 100644
--- a/src/pkg/crypto/tls/handshake_client.go
+++ b/src/pkg/crypto/tls/handshake_client.go
@@ -30,12 +30,12 @@ func (c *Conn) clientHandshake() os.Error {
 		serverName:         c.config.ServerName,
 	}
 
-	t := uint32(c.config.Time())
+	t := uint32(c.config.time())
 	hello.random[0] = byte(t >> 24)
 	hello.random[1] = byte(t >> 16)
 	hello.random[2] = byte(t >> 8)
 	hello.random[3] = byte(t)
-	_, err := io.ReadFull(c.config.Rand, hello.random[4:])
+	_, err := io.ReadFull(c.config.rand(), hello.random[4:])
 	if err != nil {
 		c.sendAlert(alertInternalError)
 		return os.ErrorString("short read from Rand")
@@ -217,12 +217,12 @@ func (c *Conn) clientHandshake() os.Error {
 	preMasterSecret := make([]byte, 48)
 	preMasterSecret[0] = byte(hello.vers >> 8)
 	preMasterSecret[1] = byte(hello.vers)
-	_, err = io.ReadFull(c.config.Rand, preMasterSecret[2:])
+	_, err = io.ReadFull(c.config.rand(), preMasterSecret[2:])
 	if err != nil {
 		return c.sendAlert(alertInternalError)
 	}
 
-	ckx.ciphertext, err = rsa.EncryptPKCS1v15(c.config.Rand, pub, preMasterSecret)
+	ckx.ciphertext, err = rsa.EncryptPKCS1v15(c.config.rand(), pub, preMasterSecret)
 	if err != nil {
 		return c.sendAlert(alertInternalError)
 	}
@@ -235,7 +235,7 @@ func (c *Conn) clientHandshake() os.Error {
 		var digest [36]byte
 		copy(digest[0:16], finishedHash.serverMD5.Sum())
 		copy(digest[16:36], finishedHash.serverSHA1.Sum())
-		signed, err := rsa.SignPKCS1v15(c.config.Rand, c.config.Certificates[0].PrivateKey, rsa.HashMD5SHA1, digest[0:])
+		signed, err := rsa.SignPKCS1v15(c.config.rand(), c.config.Certificates[0].PrivateKey, rsa.HashMD5SHA1, digest[0:])
 		if err != nil {
 			return c.sendAlert(alertInternalError)
 		}
diff --git a/src/pkg/crypto/tls/handshake_server.go b/src/pkg/crypto/tls/handshake_server.go
index 22550384610..6db2a6a1bf6 100644
--- a/src/pkg/crypto/tls/handshake_server.go
+++ b/src/pkg/crypto/tls/handshake_server.go
@@ -84,13 +84,13 @@ func (c *Conn) serverHandshake() os.Error {
 
 	hello.vers = vers
 	hello.cipherSuite = suite.id
-	t := uint32(config.Time())
+	t := uint32(config.time())
 	hello.random = make([]byte, 32)
 	hello.random[0] = byte(t >> 24)
 	hello.random[1] = byte(t >> 16)
 	hello.random[2] = byte(t >> 8)
 	hello.random[3] = byte(t)
-	_, err = io.ReadFull(config.Rand, hello.random[4:])
+	_, err = io.ReadFull(config.rand(), hello.random[4:])
 	if err != nil {
 		return c.sendAlert(alertInternalError)
 	}
@@ -209,12 +209,12 @@ func (c *Conn) serverHandshake() os.Error {
 	}
 
 	preMasterSecret := make([]byte, 48)
-	_, err = io.ReadFull(config.Rand, preMasterSecret[2:])
+	_, err = io.ReadFull(config.rand(), preMasterSecret[2:])
 	if err != nil {
 		return c.sendAlert(alertInternalError)
 	}
 
-	err = rsa.DecryptPKCS1v15SessionKey(config.Rand, config.Certificates[0].PrivateKey, ckx.ciphertext, preMasterSecret)
+	err = rsa.DecryptPKCS1v15SessionKey(config.rand(), config.Certificates[0].PrivateKey, ckx.ciphertext, preMasterSecret)
 	if err != nil {
 		return c.sendAlert(alertHandshakeFailure)
 	}
diff --git a/src/pkg/crypto/tls/tls.go b/src/pkg/crypto/tls/tls.go
index 61f0a9702dc..b11d3225daa 100644
--- a/src/pkg/crypto/tls/tls.go
+++ b/src/pkg/crypto/tls/tls.go
@@ -15,19 +15,31 @@ import (
 	"strings"
 )
 
+// Server returns a new TLS server side connection
+// using conn as the underlying transport.
+// The configuration config must be non-nil and must have
+// at least one certificate.
 func Server(conn net.Conn, config *Config) *Conn {
 	return &Conn{conn: conn, config: config}
 }
 
+// Client returns a new TLS client side connection
+// using conn as the underlying transport.
+// Client interprets a nil configuration as equivalent to
+// the zero configuration; see the documentation of Config
+// for the defaults.
 func Client(conn net.Conn, config *Config) *Conn {
 	return &Conn{conn: conn, config: config, isClient: true}
 }
 
+// A Listener implements a network listener (net.Listener) for TLS connections.
 type Listener struct {
 	listener net.Listener
 	config   *Config
 }
 
+// Accept waits for and returns the next incoming TLS connection.
+// The returned connection c is a *tls.Conn.
 func (l *Listener) Accept() (c net.Conn, err os.Error) {
 	c, err = l.listener.Accept()
 	if err != nil {
@@ -37,8 +49,10 @@ func (l *Listener) Accept() (c net.Conn, err os.Error) {
 	return
 }
 
+// Close closes the listener.
 func (l *Listener) Close() os.Error { return l.listener.Close() }
 
+// Addr returns the listener's network address.
 func (l *Listener) Addr() net.Addr { return l.listener.Addr() }
 
 // NewListener creates a Listener which accepts connections from an inner
@@ -52,7 +66,11 @@ func NewListener(listener net.Listener, config *Config) (l *Listener) {
 	return
 }
 
-func Listen(network, laddr string, config *Config) (net.Listener, os.Error) {
+// Listen creates a TLS listener accepting connections on the
+// given network address using net.Listen.
+// The configuration config must be non-nil and must have
+// at least one certificate.
+func Listen(network, laddr string, config *Config) (*Listener, os.Error) {
 	if config == nil || len(config.Certificates) == 0 {
 		return nil, os.NewError("tls.Listen: no certificates in configuration")
 	}
@@ -63,7 +81,13 @@ func Listen(network, laddr string, config *Config) (net.Listener, os.Error) {
 	return NewListener(l, config), nil
 }
 
-func Dial(network, laddr, raddr string) (net.Conn, os.Error) {
+// Dial connects to the given network address using net.Dial
+// and then initiates a TLS handshake, returning the resulting
+// TLS connection.
+// Dial interprets a nil configuration as equivalent to
+// the zero configuration; see the documentation of Config
+// for the defaults.
+func Dial(network, laddr, raddr string, config *Config) (*Conn, os.Error) {
 	c, err := net.Dial(network, laddr, raddr)
 	if err != nil {
 		return nil, err
@@ -75,15 +99,21 @@ func Dial(network, laddr, raddr string) (net.Conn, os.Error) {
 	}
 	hostname := raddr[:colonPos]
 
-	config := defaultConfig()
-	config.ServerName = hostname
-	conn := Client(c, config)
-	err = conn.Handshake()
-	if err == nil {
-		return conn, nil
+	if config == nil {
+		config = defaultConfig()
 	}
-	c.Close()
-	return nil, err
+	if config.ServerName != "" {
+		// Make a copy to avoid polluting argument or default.
+		c := *config
+		c.ServerName = hostname
+		config = &c
+	}
+	conn := Client(c, config)
+	if err = conn.Handshake(); err != nil {
+		c.Close()
+		return nil, err
+	}
+	return conn, nil
 }
 
 // LoadX509KeyPair reads and parses a public/private key pair from a pair of
diff --git a/src/pkg/http/client.go b/src/pkg/http/client.go
index e902369e7c2..29678ee32ae 100644
--- a/src/pkg/http/client.go
+++ b/src/pkg/http/client.go
@@ -63,7 +63,7 @@ func send(req *Request) (resp *Response, err os.Error) {
 			return nil, err
 		}
 	} else { // https
-		conn, err = tls.Dial("tcp", "", addr)
+		conn, err = tls.Dial("tcp", "", addr, nil)
 		if err != nil {
 			return nil, err
 		}
diff --git a/src/pkg/websocket/client.go b/src/pkg/websocket/client.go
index caf63f16f65..09134594405 100644
--- a/src/pkg/websocket/client.go
+++ b/src/pkg/websocket/client.go
@@ -111,7 +111,7 @@ func Dial(url, protocol, origin string) (ws *Conn, err os.Error) {
 		client, err = net.Dial("tcp", "", parsedUrl.Host)
 
 	case "wss":
-		client, err = tls.Dial("tcp", "", parsedUrl.Host)
+		client, err = tls.Dial("tcp", "", parsedUrl.Host, nil)
 
 	default:
 		err = ErrBadScheme