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420 lines (392 loc) · 12.5 KB
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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE-Go file.
package reality
import (
"crypto/aes"
"crypto/cipher"
"crypto/hmac"
"crypto/sha256"
"crypto/subtle"
"crypto/x509"
"errors"
"io"
"golang.org/x/crypto/cryptobyte"
)
// A SessionState is a resumable session.
type SessionState struct {
// Encoded as a SessionState (in the language of RFC 8446, Section 3).
//
// enum { server(1), client(2) } SessionStateType;
//
// opaque Certificate<1..2^24-1>;
//
// Certificate CertificateChain<0..2^24-1>;
//
// opaque Extra<0..2^24-1>;
//
// struct {
// uint16 version;
// SessionStateType type;
// uint16 cipher_suite;
// uint64 created_at;
// opaque secret<1..2^8-1>;
// Extra extra<0..2^24-1>;
// uint8 ext_master_secret = { 0, 1 };
// uint8 early_data = { 0, 1 };
// CertificateEntry certificate_list<0..2^24-1>;
// CertificateChain verified_chains<0..2^24-1>; /* excluding leaf */
// select (SessionState.early_data) {
// case 0: Empty;
// case 1: opaque alpn<1..2^8-1>;
// };
// select (SessionState.type) {
// case server: Empty;
// case client: struct {
// select (SessionState.version) {
// case VersionTLS10..VersionTLS12: Empty;
// case VersionTLS13: struct {
// uint64 use_by;
// uint32 age_add;
// };
// };
// };
// };
// } SessionState;
//
// Extra is ignored by crypto/tls, but is encoded by [SessionState.Bytes]
// and parsed by [ParseSessionState].
//
// This allows [Config.UnwrapSession]/[Config.WrapSession] and
// [ClientSessionCache] implementations to store and retrieve additional
// data alongside this session.
//
// To allow different layers in a protocol stack to share this field,
// applications must only append to it, not replace it, and must use entries
// that can be recognized even if out of order (for example, by starting
// with an id and version prefix).
Extra [][]byte
// EarlyData indicates whether the ticket can be used for 0-RTT in a QUIC
// connection. The application may set this to false if it is true to
// decline to offer 0-RTT even if supported.
EarlyData bool
version uint16
isClient bool
cipherSuite uint16
// createdAt is the generation time of the secret on the sever (which for
// TLS 1.0–1.2 might be earlier than the current session) and the time at
// which the ticket was received on the client.
createdAt uint64 // seconds since UNIX epoch
secret []byte // master secret for TLS 1.2, or the PSK for TLS 1.3
extMasterSecret bool
peerCertificates []*x509.Certificate
activeCertHandles []*activeCert
ocspResponse []byte
scts [][]byte
verifiedChains [][]*x509.Certificate
alpnProtocol string // only set if EarlyData is true
// Client-side TLS 1.3-only fields.
useBy uint64 // seconds since UNIX epoch
ageAdd uint32
}
// Bytes encodes the session, including any private fields, so that it can be
// parsed by [ParseSessionState]. The encoding contains secret values critical
// to the security of future and possibly past sessions.
//
// The specific encoding should be considered opaque and may change incompatibly
// between Go versions.
func (s *SessionState) Bytes() ([]byte, error) {
var b cryptobyte.Builder
b.AddUint16(s.version)
if s.isClient {
b.AddUint8(2) // client
} else {
b.AddUint8(1) // server
}
b.AddUint16(s.cipherSuite)
addUint64(&b, s.createdAt)
b.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddBytes(s.secret)
})
b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
for _, extra := range s.Extra {
b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddBytes(extra)
})
}
})
if s.extMasterSecret {
b.AddUint8(1)
} else {
b.AddUint8(0)
}
if s.EarlyData {
b.AddUint8(1)
} else {
b.AddUint8(0)
}
marshalCertificate(&b, Certificate{
Certificate: certificatesToBytesSlice(s.peerCertificates),
OCSPStaple: s.ocspResponse,
SignedCertificateTimestamps: s.scts,
})
b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
for _, chain := range s.verifiedChains {
b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
// We elide the first certificate because it's always the leaf.
if len(chain) == 0 {
b.SetError(errors.New("tls: internal error: empty verified chain"))
return
}
for _, cert := range chain[1:] {
b.AddUint24LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddBytes(cert.Raw)
})
}
})
}
})
if s.EarlyData {
b.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddBytes([]byte(s.alpnProtocol))
})
}
if s.isClient {
if s.version >= VersionTLS13 {
addUint64(&b, s.useBy)
b.AddUint32(s.ageAdd)
}
}
return b.Bytes()
}
func certificatesToBytesSlice(certs []*x509.Certificate) [][]byte {
s := make([][]byte, 0, len(certs))
for _, c := range certs {
s = append(s, c.Raw)
}
return s
}
// ParseSessionState parses a [SessionState] encoded by [SessionState.Bytes].
func ParseSessionState(data []byte) (*SessionState, error) {
ss := &SessionState{}
s := cryptobyte.String(data)
var typ, extMasterSecret, earlyData uint8
var cert Certificate
var extra cryptobyte.String
if !s.ReadUint16(&ss.version) ||
!s.ReadUint8(&typ) ||
(typ != 1 && typ != 2) ||
!s.ReadUint16(&ss.cipherSuite) ||
!readUint64(&s, &ss.createdAt) ||
!readUint8LengthPrefixed(&s, &ss.secret) ||
!s.ReadUint24LengthPrefixed(&extra) ||
!s.ReadUint8(&extMasterSecret) ||
!s.ReadUint8(&earlyData) ||
len(ss.secret) == 0 ||
!unmarshalCertificate(&s, &cert) {
return nil, errors.New("tls: invalid session encoding")
}
for !extra.Empty() {
var e []byte
if !readUint24LengthPrefixed(&extra, &e) {
return nil, errors.New("tls: invalid session encoding")
}
ss.Extra = append(ss.Extra, e)
}
switch extMasterSecret {
case 0:
ss.extMasterSecret = false
case 1:
ss.extMasterSecret = true
default:
return nil, errors.New("tls: invalid session encoding")
}
switch earlyData {
case 0:
ss.EarlyData = false
case 1:
ss.EarlyData = true
default:
return nil, errors.New("tls: invalid session encoding")
}
for _, cert := range cert.Certificate {
c, err := globalCertCache.newCert(cert)
if err != nil {
return nil, err
}
ss.activeCertHandles = append(ss.activeCertHandles, c)
ss.peerCertificates = append(ss.peerCertificates, c.cert)
}
ss.ocspResponse = cert.OCSPStaple
ss.scts = cert.SignedCertificateTimestamps
var chainList cryptobyte.String
if !s.ReadUint24LengthPrefixed(&chainList) {
return nil, errors.New("tls: invalid session encoding")
}
for !chainList.Empty() {
var certList cryptobyte.String
if !chainList.ReadUint24LengthPrefixed(&certList) {
return nil, errors.New("tls: invalid session encoding")
}
var chain []*x509.Certificate
if len(ss.peerCertificates) == 0 {
return nil, errors.New("tls: invalid session encoding")
}
chain = append(chain, ss.peerCertificates[0])
for !certList.Empty() {
var cert []byte
if !readUint24LengthPrefixed(&certList, &cert) {
return nil, errors.New("tls: invalid session encoding")
}
c, err := globalCertCache.newCert(cert)
if err != nil {
return nil, err
}
ss.activeCertHandles = append(ss.activeCertHandles, c)
chain = append(chain, c.cert)
}
ss.verifiedChains = append(ss.verifiedChains, chain)
}
if ss.EarlyData {
var alpn []byte
if !readUint8LengthPrefixed(&s, &alpn) {
return nil, errors.New("tls: invalid session encoding")
}
ss.alpnProtocol = string(alpn)
}
if isClient := typ == 2; !isClient {
if !s.Empty() {
return nil, errors.New("tls: invalid session encoding")
}
return ss, nil
}
ss.isClient = true
if len(ss.peerCertificates) == 0 {
return nil, errors.New("tls: no server certificates in client session")
}
if ss.version < VersionTLS13 {
if !s.Empty() {
return nil, errors.New("tls: invalid session encoding")
}
return ss, nil
}
if !s.ReadUint64(&ss.useBy) || !s.ReadUint32(&ss.ageAdd) || !s.Empty() {
return nil, errors.New("tls: invalid session encoding")
}
return ss, nil
}
// sessionState returns a partially filled-out [SessionState] with information
// from the current connection.
func (c *Conn) sessionState() (*SessionState, error) {
return &SessionState{
version: c.vers,
cipherSuite: c.cipherSuite,
createdAt: uint64(c.config.time().Unix()),
alpnProtocol: c.clientProtocol,
peerCertificates: c.peerCertificates,
activeCertHandles: c.activeCertHandles,
ocspResponse: c.ocspResponse,
scts: c.scts,
isClient: c.isClient,
extMasterSecret: c.extMasterSecret,
verifiedChains: c.verifiedChains,
}, nil
}
// EncryptTicket encrypts a ticket with the [Config]'s configured (or default)
// session ticket keys. It can be used as a [Config.WrapSession] implementation.
func (c *Config) EncryptTicket(cs ConnectionState, ss *SessionState) ([]byte, error) {
ticketKeys := c.ticketKeys(nil)
stateBytes, err := ss.Bytes()
if err != nil {
return nil, err
}
return c.encryptTicket(stateBytes, ticketKeys)
}
func (c *Config) encryptTicket(state []byte, ticketKeys []ticketKey) ([]byte, error) {
if len(ticketKeys) == 0 {
return nil, errors.New("tls: internal error: session ticket keys unavailable")
}
encrypted := make([]byte, aes.BlockSize+len(state)+sha256.Size)
iv := encrypted[:aes.BlockSize]
ciphertext := encrypted[aes.BlockSize : len(encrypted)-sha256.Size]
authenticated := encrypted[:len(encrypted)-sha256.Size]
macBytes := encrypted[len(encrypted)-sha256.Size:]
if _, err := io.ReadFull(c.rand(), iv); err != nil {
return nil, err
}
key := ticketKeys[0]
block, err := aes.NewCipher(key.aesKey[:])
if err != nil {
return nil, errors.New("tls: failed to create cipher while encrypting ticket: " + err.Error())
}
cipher.NewCTR(block, iv).XORKeyStream(ciphertext, state)
mac := hmac.New(sha256.New, key.hmacKey[:])
mac.Write(authenticated)
mac.Sum(macBytes[:0])
return encrypted, nil
}
// DecryptTicket decrypts a ticket encrypted by [Config.EncryptTicket]. It can
// be used as a [Config.UnwrapSession] implementation.
//
// If the ticket can't be decrypted or parsed, DecryptTicket returns (nil, nil).
func (c *Config) DecryptTicket(identity []byte, cs ConnectionState) (*SessionState, error) {
ticketKeys := c.ticketKeys(nil)
stateBytes := c.decryptTicket(identity, ticketKeys)
if stateBytes == nil {
return nil, nil
}
s, err := ParseSessionState(stateBytes)
if err != nil {
return nil, nil // drop unparsable tickets on the floor
}
return s, nil
}
func (c *Config) decryptTicket(encrypted []byte, ticketKeys []ticketKey) []byte {
if len(encrypted) < aes.BlockSize+sha256.Size {
return nil
}
iv := encrypted[:aes.BlockSize]
ciphertext := encrypted[aes.BlockSize : len(encrypted)-sha256.Size]
authenticated := encrypted[:len(encrypted)-sha256.Size]
macBytes := encrypted[len(encrypted)-sha256.Size:]
for _, key := range ticketKeys {
mac := hmac.New(sha256.New, key.hmacKey[:])
mac.Write(authenticated)
expected := mac.Sum(nil)
if subtle.ConstantTimeCompare(macBytes, expected) != 1 {
continue
}
block, err := aes.NewCipher(key.aesKey[:])
if err != nil {
return nil
}
plaintext := make([]byte, len(ciphertext))
cipher.NewCTR(block, iv).XORKeyStream(plaintext, ciphertext)
return plaintext
}
return nil
}
// ClientSessionState contains the state needed by a client to
// resume a previous TLS session.
type ClientSessionState struct {
ticket []byte
session *SessionState
}
// ResumptionState returns the session ticket sent by the server (also known as
// the session's identity) and the state necessary to resume this session.
//
// It can be called by [ClientSessionCache.Put] to serialize (with
// [SessionState.Bytes]) and store the session.
func (cs *ClientSessionState) ResumptionState() (ticket []byte, state *SessionState, err error) {
return cs.ticket, cs.session, nil
}
// NewResumptionState returns a state value that can be returned by
// [ClientSessionCache.Get] to resume a previous session.
//
// state needs to be returned by [ParseSessionState], and the ticket and session
// state must have been returned by [ClientSessionState.ResumptionState].
func NewResumptionState(ticket []byte, state *SessionState) (*ClientSessionState, error) {
return &ClientSessionState{
ticket: ticket, session: state,
}, nil
}
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