1 // Copyright 2012 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
17 "golang.org/x/crypto/cryptobyte"
20 // A SessionState is a resumable session.
21 type SessionState struct {
22 // Encoded as a SessionState (in the language of RFC 8446, Section 3).
24 // enum { server(1), client(2) } SessionStateType;
26 // opaque Certificate<1..2^24-1>;
28 // Certificate CertificateChain<0..2^24-1>;
32 // SessionStateType type;
33 // uint16 cipher_suite;
35 // opaque secret<1..2^8-1>;
36 // opaque extra<0..2^24-1>;
37 // uint8 ext_master_secret = { 0, 1 };
38 // uint8 early_data = { 0, 1 };
39 // CertificateEntry certificate_list<0..2^24-1>;
40 // select (SessionState.early_data) {
42 // case 1: opaque alpn<1..2^8-1>;
44 // select (SessionState.type) {
45 // case server: /* empty */;
46 // case client: struct {
47 // CertificateChain verified_chains<0..2^24-1>; /* excluding leaf */
48 // select (SessionState.version) {
49 // case VersionTLS10..VersionTLS12: /* empty */;
50 // case VersionTLS13: struct {
60 // Extra is ignored by crypto/tls, but is encoded by [SessionState.Bytes]
61 // and parsed by [ParseSessionState].
63 // This allows [Config.UnwrapSession]/[Config.WrapSession] and
64 // [ClientSessionCache] implementations to store and retrieve additional
67 // If Extra is already set, the implementation must preserve the previous
68 // value across a round-trip, for example by appending and stripping a
69 // fixed-length suffix.
72 // EarlyData indicates whether the ticket can be used for 0-RTT in a QUIC
73 // connection. The application may set this to false if it is true to
74 // decline to offer 0-RTT even if supported.
80 // createdAt is the generation time of the secret on the sever (which for
81 // TLS 1.0–1.2 might be earlier than the current session) and the time at
82 // which the ticket was received on the client.
83 createdAt uint64 // seconds since UNIX epoch
84 secret []byte // master secret for TLS 1.2, or the PSK for TLS 1.3
86 peerCertificates []*x509.Certificate
87 activeCertHandles []*activeCert
90 alpnProtocol string // only set if EarlyData is true
92 // Client-side fields.
93 verifiedChains [][]*x509.Certificate
95 // Client-side TLS 1.3-only fields.
96 useBy uint64 // seconds since UNIX epoch
100 // Bytes encodes the session, including any private fields, so that it can be
101 // parsed by [ParseSessionState]. The encoding contains secret values critical
102 // to the security of future and possibly past sessions.
104 // The specific encoding should be considered opaque and may change incompatibly
105 // between Go versions.
106 func (s *SessionState) Bytes() ([]byte, error) {
107 var b cryptobyte.Builder
108 b.AddUint16(s.version)
110 b.AddUint8(2) // client
112 b.AddUint8(1) // server
114 b.AddUint16(s.cipherSuite)
115 addUint64(&b, s.createdAt)
116 b.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
119 b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
122 if s.extMasterSecret {
132 marshalCertificate(&b, s.certificate())
134 b.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
135 b.AddBytes([]byte(s.alpnProtocol))
139 b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
140 for _, chain := range s.verifiedChains {
141 b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
142 // We elide the first certificate because it's always the leaf.
144 b.SetError(errors.New("tls: internal error: empty verified chain"))
147 for _, cert := range chain[1:] {
148 b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
155 if s.version >= VersionTLS13 {
156 addUint64(&b, s.useBy)
157 b.AddUint32(s.ageAdd)
163 func (s *SessionState) certificate() Certificate {
165 Certificate: certificatesToBytesSlice(s.peerCertificates),
166 OCSPStaple: s.ocspResponse,
167 SignedCertificateTimestamps: s.scts,
171 func certificatesToBytesSlice(certs []*x509.Certificate) [][]byte {
172 s := make([][]byte, 0, len(certs))
173 for _, c := range certs {
179 // ParseSessionState parses a [SessionState] encoded by [SessionState.Bytes].
180 func ParseSessionState(data []byte) (*SessionState, error) {
181 ss := &SessionState{}
182 s := cryptobyte.String(data)
183 var typ, extMasterSecret, earlyData uint8
185 if !s.ReadUint16(&ss.version) ||
186 !s.ReadUint8(&typ) ||
187 (typ != 1 && typ != 2) ||
188 !s.ReadUint16(&ss.cipherSuite) ||
189 !readUint64(&s, &ss.createdAt) ||
190 !readUint8LengthPrefixed(&s, &ss.secret) ||
191 !readUint24LengthPrefixed(&s, &ss.Extra) ||
192 !s.ReadUint8(&extMasterSecret) ||
193 !s.ReadUint8(&earlyData) ||
194 len(ss.secret) == 0 ||
195 !unmarshalCertificate(&s, &cert) {
196 return nil, errors.New("tls: invalid session encoding")
198 switch extMasterSecret {
200 ss.extMasterSecret = false
202 ss.extMasterSecret = true
204 return nil, errors.New("tls: invalid session encoding")
212 return nil, errors.New("tls: invalid session encoding")
214 for _, cert := range cert.Certificate {
215 c, err := globalCertCache.newCert(cert)
219 ss.activeCertHandles = append(ss.activeCertHandles, c)
220 ss.peerCertificates = append(ss.peerCertificates, c.cert)
222 ss.ocspResponse = cert.OCSPStaple
223 ss.scts = cert.SignedCertificateTimestamps
226 if !readUint8LengthPrefixed(&s, &alpn) {
227 return nil, errors.New("tls: invalid session encoding")
229 ss.alpnProtocol = string(alpn)
231 if isClient := typ == 2; !isClient {
233 return nil, errors.New("tls: invalid session encoding")
238 if len(ss.peerCertificates) == 0 {
239 return nil, errors.New("tls: no server certificates in client session")
241 var chainList cryptobyte.String
242 if !s.ReadUint24LengthPrefixed(&chainList) {
243 return nil, errors.New("tls: invalid session encoding")
245 for !chainList.Empty() {
246 var certList cryptobyte.String
247 if !chainList.ReadUint24LengthPrefixed(&certList) {
248 return nil, errors.New("tls: invalid session encoding")
250 var chain []*x509.Certificate
251 chain = append(chain, ss.peerCertificates[0])
252 for !certList.Empty() {
254 if !readUint24LengthPrefixed(&certList, &cert) {
255 return nil, errors.New("tls: invalid session encoding")
257 c, err := globalCertCache.newCert(cert)
261 ss.activeCertHandles = append(ss.activeCertHandles, c)
262 chain = append(chain, c.cert)
264 ss.verifiedChains = append(ss.verifiedChains, chain)
266 if ss.version < VersionTLS13 {
268 return nil, errors.New("tls: invalid session encoding")
272 if !s.ReadUint64(&ss.useBy) || !s.ReadUint32(&ss.ageAdd) || !s.Empty() {
273 return nil, errors.New("tls: invalid session encoding")
278 // sessionState returns a partially filled-out [SessionState] with information
279 // from the current connection.
280 func (c *Conn) sessionState() (*SessionState, error) {
281 var verifiedChains [][]*x509.Certificate
283 verifiedChains = c.verifiedChains
284 if len(c.peerCertificates) == 0 {
285 return nil, errors.New("tls: internal error: empty peer certificates")
288 return &SessionState{
290 cipherSuite: c.cipherSuite,
291 createdAt: uint64(c.config.time().Unix()),
292 alpnProtocol: c.clientProtocol,
293 peerCertificates: c.peerCertificates,
294 activeCertHandles: c.activeCertHandles,
295 ocspResponse: c.ocspResponse,
297 isClient: c.isClient,
298 extMasterSecret: c.extMasterSecret,
299 verifiedChains: verifiedChains,
303 // EncryptTicket encrypts a ticket with the Config's configured (or default)
304 // session ticket keys. It can be used as a [Config.WrapSession] implementation.
305 func (c *Config) EncryptTicket(cs ConnectionState, ss *SessionState) ([]byte, error) {
306 ticketKeys := c.ticketKeys(nil)
307 stateBytes, err := ss.Bytes()
311 return c.encryptTicket(stateBytes, ticketKeys)
314 var _ = &Config{WrapSession: (&Config{}).EncryptTicket}
316 func (c *Config) encryptTicket(state []byte, ticketKeys []ticketKey) ([]byte, error) {
317 if len(ticketKeys) == 0 {
318 return nil, errors.New("tls: internal error: session ticket keys unavailable")
321 encrypted := make([]byte, aes.BlockSize+len(state)+sha256.Size)
322 iv := encrypted[:aes.BlockSize]
323 ciphertext := encrypted[aes.BlockSize : len(encrypted)-sha256.Size]
324 authenticated := encrypted[:len(encrypted)-sha256.Size]
325 macBytes := encrypted[len(encrypted)-sha256.Size:]
327 if _, err := io.ReadFull(c.rand(), iv); err != nil {
331 block, err := aes.NewCipher(key.aesKey[:])
333 return nil, errors.New("tls: failed to create cipher while encrypting ticket: " + err.Error())
335 cipher.NewCTR(block, iv).XORKeyStream(ciphertext, state)
337 mac := hmac.New(sha256.New, key.hmacKey[:])
338 mac.Write(authenticated)
339 mac.Sum(macBytes[:0])
341 return encrypted, nil
344 // DecryptTicket decrypts a ticket encrypted by [Config.EncryptTicket]. It can
345 // be used as a [Config.UnwrapSession] implementation.
347 // If the ticket can't be decrypted or parsed, DecryptTicket returns (nil, nil).
348 func (c *Config) DecryptTicket(identity []byte, cs ConnectionState) (*SessionState, error) {
349 ticketKeys := c.ticketKeys(nil)
350 stateBytes := c.decryptTicket(identity, ticketKeys)
351 if stateBytes == nil {
354 s, err := ParseSessionState(stateBytes)
356 return nil, nil // drop unparsable tickets on the floor
361 var _ = &Config{UnwrapSession: (&Config{}).DecryptTicket}
363 func (c *Config) decryptTicket(encrypted []byte, ticketKeys []ticketKey) []byte {
364 if len(encrypted) < aes.BlockSize+sha256.Size {
368 iv := encrypted[:aes.BlockSize]
369 ciphertext := encrypted[aes.BlockSize : len(encrypted)-sha256.Size]
370 authenticated := encrypted[:len(encrypted)-sha256.Size]
371 macBytes := encrypted[len(encrypted)-sha256.Size:]
373 for _, key := range ticketKeys {
374 mac := hmac.New(sha256.New, key.hmacKey[:])
375 mac.Write(authenticated)
376 expected := mac.Sum(nil)
378 if subtle.ConstantTimeCompare(macBytes, expected) != 1 {
382 block, err := aes.NewCipher(key.aesKey[:])
386 plaintext := make([]byte, len(ciphertext))
387 cipher.NewCTR(block, iv).XORKeyStream(plaintext, ciphertext)
395 // ClientSessionState contains the state needed by a client to
396 // resume a previous TLS session.
397 type ClientSessionState struct {
399 session *SessionState
402 // ResumptionState returns the session ticket sent by the server (also known as
403 // the session's identity) and the state necessary to resume this session.
405 // It can be called by [ClientSessionCache.Put] to serialize (with
406 // [SessionState.Bytes]) and store the session.
407 func (cs *ClientSessionState) ResumptionState() (ticket []byte, state *SessionState, err error) {
408 return cs.ticket, cs.session, nil
411 // NewResumptionState returns a state value that can be returned by
412 // [ClientSessionCache.Get] to resume a previous session.
414 // state needs to be returned by [ParseSessionState], and the ticket and session
415 // state must have been returned by [ClientSessionState.ResumptionState].
416 func NewResumptionState(ticket []byte, state *SessionState) (*ClientSessionState, error) {
417 return &ClientSessionState{
418 ticket: ticket, session: state,