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 // CertificateEntry certificate_list<0..2^24-1>;
38 // select (SessionState.type) {
39 // case server: /* empty */;
40 // case client: struct {
41 // CertificateChain verified_chains<0..2^24-1>; /* excluding leaf */
42 // select (SessionState.version) {
43 // case VersionTLS10..VersionTLS12: /* empty */;
44 // case VersionTLS13: struct {
54 // Extra is ignored by crypto/tls, but is encoded by [SessionState.Bytes]
55 // and parsed by [ParseSessionState].
57 // This allows [Config.UnwrapSession]/[Config.WrapSession] and
58 // [ClientSessionCache] implementations to store and retrieve additional
61 // If Extra is already set, the implementation must preserve the previous
62 // value across a round-trip, for example by appending and stripping a
63 // fixed-length suffix.
69 // createdAt is the generation time of the secret on the sever (which for
70 // TLS 1.0–1.2 might be earlier than the current session) and the time at
71 // which the ticket was received on the client.
72 createdAt uint64 // seconds since UNIX epoch
73 secret []byte // master secret for TLS 1.2, or the PSK for TLS 1.3
74 peerCertificates []*x509.Certificate
75 activeCertHandles []*activeCert
79 // Client-side fields.
80 verifiedChains [][]*x509.Certificate
82 // Client-side TLS 1.3-only fields.
83 useBy uint64 // seconds since UNIX epoch
87 // Bytes encodes the session, including any private fields, so that it can be
88 // parsed by [ParseSessionState]. The encoding contains secret values critical
89 // to the security of future and possibly past sessions.
91 // The specific encoding should be considered opaque and may change incompatibly
92 // between Go versions.
93 func (s *SessionState) Bytes() ([]byte, error) {
94 var b cryptobyte.Builder
95 b.AddUint16(s.version)
97 b.AddUint8(2) // client
99 b.AddUint8(1) // server
101 b.AddUint16(s.cipherSuite)
102 addUint64(&b, s.createdAt)
103 b.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
106 b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
109 marshalCertificate(&b, s.certificate())
111 b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
112 for _, chain := range s.verifiedChains {
113 b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
114 // We elide the first certificate because it's always the leaf.
116 b.SetError(errors.New("tls: internal error: empty verified chain"))
119 for _, cert := range chain[1:] {
120 b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
127 if s.version >= VersionTLS13 {
128 addUint64(&b, s.useBy)
129 b.AddUint32(s.ageAdd)
135 func (s *SessionState) certificate() Certificate {
137 Certificate: certificatesToBytesSlice(s.peerCertificates),
138 OCSPStaple: s.ocspResponse,
139 SignedCertificateTimestamps: s.scts,
143 func certificatesToBytesSlice(certs []*x509.Certificate) [][]byte {
144 s := make([][]byte, 0, len(certs))
145 for _, c := range certs {
151 // ParseSessionState parses a [SessionState] encoded by [SessionState.Bytes].
152 func ParseSessionState(data []byte) (*SessionState, error) {
153 ss := &SessionState{}
154 s := cryptobyte.String(data)
157 if !s.ReadUint16(&ss.version) ||
158 !s.ReadUint8(&typ) ||
159 (typ != 1 && typ != 2) ||
160 !s.ReadUint16(&ss.cipherSuite) ||
161 !readUint64(&s, &ss.createdAt) ||
162 !readUint8LengthPrefixed(&s, &ss.secret) ||
163 !readUint24LengthPrefixed(&s, &ss.Extra) ||
164 len(ss.secret) == 0 ||
165 !unmarshalCertificate(&s, &cert) {
166 return nil, errors.New("tls: invalid session encoding")
168 for _, cert := range cert.Certificate {
169 c, err := globalCertCache.newCert(cert)
173 ss.activeCertHandles = append(ss.activeCertHandles, c)
174 ss.peerCertificates = append(ss.peerCertificates, c.cert)
176 ss.ocspResponse = cert.OCSPStaple
177 ss.scts = cert.SignedCertificateTimestamps
178 if isClient := typ == 2; !isClient {
180 return nil, errors.New("tls: invalid session encoding")
185 if len(ss.peerCertificates) == 0 {
186 return nil, errors.New("tls: no server certificates in client session")
188 var chainList cryptobyte.String
189 if !s.ReadUint24LengthPrefixed(&chainList) {
190 return nil, errors.New("tls: invalid session encoding")
192 for !chainList.Empty() {
193 var certList cryptobyte.String
194 if !chainList.ReadUint24LengthPrefixed(&certList) {
195 return nil, errors.New("tls: invalid session encoding")
197 var chain []*x509.Certificate
198 chain = append(chain, ss.peerCertificates[0])
199 for !certList.Empty() {
201 if !readUint24LengthPrefixed(&certList, &cert) {
202 return nil, errors.New("tls: invalid session encoding")
204 c, err := globalCertCache.newCert(cert)
208 ss.activeCertHandles = append(ss.activeCertHandles, c)
209 chain = append(chain, c.cert)
211 ss.verifiedChains = append(ss.verifiedChains, chain)
213 if ss.version < VersionTLS13 {
215 return nil, errors.New("tls: invalid session encoding")
219 if !s.ReadUint64(&ss.useBy) || !s.ReadUint32(&ss.ageAdd) || !s.Empty() {
220 return nil, errors.New("tls: invalid session encoding")
225 // sessionState returns a partially filled-out [SessionState] with information
226 // from the current connection.
227 func (c *Conn) sessionState() (*SessionState, error) {
228 var verifiedChains [][]*x509.Certificate
230 verifiedChains = c.verifiedChains
231 if len(c.peerCertificates) == 0 {
232 return nil, errors.New("tls: internal error: empty peer certificates")
235 return &SessionState{
237 cipherSuite: c.cipherSuite,
238 createdAt: uint64(c.config.time().Unix()),
239 peerCertificates: c.peerCertificates,
240 activeCertHandles: c.activeCertHandles,
241 ocspResponse: c.ocspResponse,
243 isClient: c.isClient,
244 verifiedChains: verifiedChains,
248 // EncryptTicket encrypts a ticket with the Config's configured (or default)
249 // session ticket keys. It can be used as a [Config.WrapSession] implementation.
250 func (c *Config) EncryptTicket(cs ConnectionState, ss *SessionState) ([]byte, error) {
251 ticketKeys := c.ticketKeys(nil)
252 stateBytes, err := ss.Bytes()
256 return c.encryptTicket(stateBytes, ticketKeys)
259 var _ = &Config{WrapSession: (&Config{}).EncryptTicket}
261 func (c *Config) encryptTicket(state []byte, ticketKeys []ticketKey) ([]byte, error) {
262 if len(ticketKeys) == 0 {
263 return nil, errors.New("tls: internal error: session ticket keys unavailable")
266 encrypted := make([]byte, aes.BlockSize+len(state)+sha256.Size)
267 iv := encrypted[:aes.BlockSize]
268 ciphertext := encrypted[aes.BlockSize : len(encrypted)-sha256.Size]
269 authenticated := encrypted[:len(encrypted)-sha256.Size]
270 macBytes := encrypted[len(encrypted)-sha256.Size:]
272 if _, err := io.ReadFull(c.rand(), iv); err != nil {
276 block, err := aes.NewCipher(key.aesKey[:])
278 return nil, errors.New("tls: failed to create cipher while encrypting ticket: " + err.Error())
280 cipher.NewCTR(block, iv).XORKeyStream(ciphertext, state)
282 mac := hmac.New(sha256.New, key.hmacKey[:])
283 mac.Write(authenticated)
284 mac.Sum(macBytes[:0])
286 return encrypted, nil
289 // DecryptTicket decrypts a ticket encrypted by [Config.EncryptTicket]. It can
290 // be used as a [Config.UnwrapSession] implementation.
292 // If the ticket can't be decrypted or parsed, DecryptTicket returns (nil, nil).
293 func (c *Config) DecryptTicket(identity []byte, cs ConnectionState) (*SessionState, error) {
294 ticketKeys := c.ticketKeys(nil)
295 stateBytes := c.decryptTicket(identity, ticketKeys)
296 if stateBytes == nil {
299 s, err := ParseSessionState(stateBytes)
301 return nil, nil // drop unparsable tickets on the floor
306 var _ = &Config{UnwrapSession: (&Config{}).DecryptTicket}
308 func (c *Config) decryptTicket(encrypted []byte, ticketKeys []ticketKey) []byte {
309 if len(encrypted) < aes.BlockSize+sha256.Size {
313 iv := encrypted[:aes.BlockSize]
314 ciphertext := encrypted[aes.BlockSize : len(encrypted)-sha256.Size]
315 authenticated := encrypted[:len(encrypted)-sha256.Size]
316 macBytes := encrypted[len(encrypted)-sha256.Size:]
318 for _, key := range ticketKeys {
319 mac := hmac.New(sha256.New, key.hmacKey[:])
320 mac.Write(authenticated)
321 expected := mac.Sum(nil)
323 if subtle.ConstantTimeCompare(macBytes, expected) != 1 {
327 block, err := aes.NewCipher(key.aesKey[:])
331 plaintext := make([]byte, len(ciphertext))
332 cipher.NewCTR(block, iv).XORKeyStream(plaintext, ciphertext)
340 // ClientSessionState contains the state needed by a client to
341 // resume a previous TLS session.
342 type ClientSessionState struct {
344 session *SessionState
347 // ResumptionState returns the session ticket sent by the server (also known as
348 // the session's identity) and the state necessary to resume this session.
350 // It can be called by [ClientSessionCache.Put] to serialize (with
351 // [SessionState.Bytes]) and store the session.
352 func (cs *ClientSessionState) ResumptionState() (ticket []byte, state *SessionState, err error) {
353 return cs.ticket, cs.session, nil
356 // NewResumptionState returns a state value that can be returned by
357 // [ClientSessionCache.Get] to resume a previous session.
359 // state needs to be returned by [ParseSessionState], and the ticket and session
360 // state must have been returned by [ClientSessionState.ResumptionState].
361 func NewResumptionState(ticket []byte, state *SessionState) (*ClientSessionState, error) {
362 return &ClientSessionState{
363 ticket: ticket, session: state,