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key_agreement.go
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key_agreement.go
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// Copyright 2010 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 file.
package runner
import (
"crypto"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/elliptic"
"crypto/rsa"
"crypto/subtle"
"crypto/x509"
"errors"
"fmt"
"io"
"math/big"
"boringssl.googlesource.com/boringssl/ssl/test/runner/kyber"
"golang.org/x/crypto/curve25519"
)
type keyType int
const (
keyTypeRSA keyType = iota + 1
keyTypeECDSA
)
var errClientKeyExchange = errors.New("tls: invalid ClientKeyExchange message")
var errServerKeyExchange = errors.New("tls: invalid ServerKeyExchange message")
// rsaKeyAgreement implements the standard TLS key agreement where the client
// encrypts the pre-master secret to the server's public key.
type rsaKeyAgreement struct {
version uint16
clientVersion uint16
exportKey *rsa.PrivateKey
}
func (ka *rsaKeyAgreement) generateServerKeyExchange(config *Config, cert *Credential, clientHello *clientHelloMsg, hello *serverHelloMsg, version uint16) (*serverKeyExchangeMsg, error) {
// Save the client version for comparison later.
ka.clientVersion = clientHello.vers
if !config.Bugs.RSAEphemeralKey {
return nil, nil
}
// Generate an ephemeral RSA key to use instead of the real
// one, as in RSA_EXPORT.
key, err := rsa.GenerateKey(config.rand(), 512)
if err != nil {
return nil, err
}
ka.exportKey = key
modulus := key.N.Bytes()
exponent := big.NewInt(int64(key.E)).Bytes()
serverRSAParams := make([]byte, 0, 2+len(modulus)+2+len(exponent))
serverRSAParams = append(serverRSAParams, byte(len(modulus)>>8), byte(len(modulus)))
serverRSAParams = append(serverRSAParams, modulus...)
serverRSAParams = append(serverRSAParams, byte(len(exponent)>>8), byte(len(exponent)))
serverRSAParams = append(serverRSAParams, exponent...)
var sigAlg signatureAlgorithm
if ka.version >= VersionTLS12 {
sigAlg, err = selectSignatureAlgorithm(false /* server */, ka.version, cert, config, clientHello.signatureAlgorithms)
if err != nil {
return nil, err
}
}
sig, err := signMessage(false /* server */, ka.version, cert.PrivateKey, config, sigAlg, serverRSAParams)
if err != nil {
return nil, errors.New("failed to sign RSA parameters: " + err.Error())
}
skx := new(serverKeyExchangeMsg)
sigAlgsLen := 0
if ka.version >= VersionTLS12 {
sigAlgsLen = 2
}
skx.key = make([]byte, len(serverRSAParams)+sigAlgsLen+2+len(sig))
copy(skx.key, serverRSAParams)
k := skx.key[len(serverRSAParams):]
if ka.version >= VersionTLS12 {
k[0] = byte(sigAlg >> 8)
k[1] = byte(sigAlg)
k = k[2:]
}
k[0] = byte(len(sig) >> 8)
k[1] = byte(len(sig))
copy(k[2:], sig)
return skx, nil
}
func (ka *rsaKeyAgreement) processClientKeyExchange(config *Config, cert *Credential, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
preMasterSecret := make([]byte, 48)
_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
if err != nil {
return nil, err
}
if len(ckx.ciphertext) < 2 {
return nil, errClientKeyExchange
}
ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1])
if ciphertextLen != len(ckx.ciphertext)-2 {
return nil, errClientKeyExchange
}
ciphertext := ckx.ciphertext[2:]
key := cert.PrivateKey.(*rsa.PrivateKey)
if ka.exportKey != nil {
key = ka.exportKey
}
err = rsa.DecryptPKCS1v15SessionKey(config.rand(), key, ciphertext, preMasterSecret)
if err != nil {
return nil, err
}
// This check should be done in constant-time, but this is a testing
// implementation. See the discussion at the end of section 7.4.7.1 of
// RFC 4346.
vers := uint16(preMasterSecret[0])<<8 | uint16(preMasterSecret[1])
if ka.clientVersion != vers {
return nil, fmt.Errorf("tls: invalid version in RSA premaster (got %04x, wanted %04x)", vers, ka.clientVersion)
}
return preMasterSecret, nil
}
func (ka *rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, key crypto.PublicKey, skx *serverKeyExchangeMsg) error {
return errors.New("tls: unexpected ServerKeyExchange")
}
func rsaSize(pub *rsa.PublicKey) int {
return (pub.N.BitLen() + 7) / 8
}
func rsaRawEncrypt(pub *rsa.PublicKey, msg []byte) ([]byte, error) {
k := rsaSize(pub)
if len(msg) != k {
return nil, errors.New("tls: bad padded RSA input")
}
m := new(big.Int).SetBytes(msg)
e := big.NewInt(int64(pub.E))
m.Exp(m, e, pub.N)
unpadded := m.Bytes()
ret := make([]byte, k)
copy(ret[len(ret)-len(unpadded):], unpadded)
return ret, nil
}
// nonZeroRandomBytes fills the given slice with non-zero random octets.
func nonZeroRandomBytes(s []byte, rand io.Reader) {
if _, err := io.ReadFull(rand, s); err != nil {
panic(err)
}
for i := range s {
for s[i] == 0 {
if _, err := io.ReadFull(rand, s[i:i+1]); err != nil {
panic(err)
}
}
}
}
func (ka *rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
bad := config.Bugs.BadRSAClientKeyExchange
preMasterSecret := make([]byte, 48)
vers := clientHello.vers
if bad == RSABadValueWrongVersion1 {
vers ^= 1
} else if bad == RSABadValueWrongVersion2 {
vers ^= 0x100
}
preMasterSecret[0] = byte(vers >> 8)
preMasterSecret[1] = byte(vers)
_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
if err != nil {
return nil, nil, err
}
sentPreMasterSecret := preMasterSecret
if bad == RSABadValueTooLong {
sentPreMasterSecret = make([]byte, 1, len(sentPreMasterSecret)+1)
sentPreMasterSecret = append(sentPreMasterSecret, preMasterSecret...)
} else if bad == RSABadValueTooShort {
sentPreMasterSecret = sentPreMasterSecret[:len(sentPreMasterSecret)-1]
}
// Pad for PKCS#1 v1.5.
padded := make([]byte, rsaSize(cert.PublicKey.(*rsa.PublicKey)))
padded[1] = 2
nonZeroRandomBytes(padded[2:len(padded)-len(sentPreMasterSecret)-1], config.rand())
copy(padded[len(padded)-len(sentPreMasterSecret):], sentPreMasterSecret)
if bad == RSABadValueWrongBlockType {
padded[1] = 3
} else if bad == RSABadValueWrongLeadingByte {
padded[0] = 1
} else if bad == RSABadValueNoZero {
for i := 2; i < len(padded); i++ {
if padded[i] == 0 {
padded[i]++
}
}
}
encrypted, err := rsaRawEncrypt(cert.PublicKey.(*rsa.PublicKey), padded)
if err != nil {
return nil, nil, err
}
if bad == RSABadValueCorrupt {
encrypted[len(encrypted)-1] ^= 1
// Clear the high byte to ensure |encrypted| is still below the RSA modulus.
encrypted[0] = 0
}
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, len(encrypted)+2)
ckx.ciphertext[0] = byte(len(encrypted) >> 8)
ckx.ciphertext[1] = byte(len(encrypted))
copy(ckx.ciphertext[2:], encrypted)
return preMasterSecret, ckx, nil
}
func (ka *rsaKeyAgreement) peerSignatureAlgorithm() signatureAlgorithm {
return 0
}
// A kemImplementation is an instance of KEM-style construction for TLS.
type kemImplementation interface {
// generate generates a keypair using rand. It returns the encoded public key.
generate(rand io.Reader) (publicKey []byte, err error)
// encap generates a symmetric, shared secret, encapsulates it with |peerKey|.
// It returns the encapsulated shared secret and the secret itself.
encap(rand io.Reader, peerKey []byte) (ciphertext []byte, secret []byte, err error)
// decap decapsulates |ciphertext| and returns the resulting shared secret.
decap(ciphertext []byte) (secret []byte, err error)
}
// ecdhKEM implements kemImplementation with an elliptic.Curve.
//
// TODO(davidben): Move this to Go's crypto/ecdh.
type ecdhKEM struct {
curve elliptic.Curve
privateKey []byte
sendCompressed bool
}
func (e *ecdhKEM) generate(rand io.Reader) (publicKey []byte, err error) {
var x, y *big.Int
e.privateKey, x, y, err = elliptic.GenerateKey(e.curve, rand)
if err != nil {
return nil, err
}
ret := elliptic.Marshal(e.curve, x, y)
if e.sendCompressed {
l := (len(ret) - 1) / 2
tmp := make([]byte, 1+l)
tmp[0] = byte(2 | y.Bit(0))
copy(tmp[1:], ret[1:1+l])
ret = tmp
}
return ret, nil
}
func (e *ecdhKEM) encap(rand io.Reader, peerKey []byte) (ciphertext []byte, secret []byte, err error) {
ciphertext, err = e.generate(rand)
if err != nil {
return nil, nil, err
}
secret, err = e.decap(peerKey)
if err != nil {
return nil, nil, err
}
return
}
func (e *ecdhKEM) decap(ciphertext []byte) (secret []byte, err error) {
x, y := elliptic.Unmarshal(e.curve, ciphertext)
if x == nil {
return nil, errors.New("tls: invalid peer key")
}
x, _ = e.curve.ScalarMult(x, y, e.privateKey)
secret = make([]byte, (e.curve.Params().BitSize+7)>>3)
xBytes := x.Bytes()
copy(secret[len(secret)-len(xBytes):], xBytes)
return secret, nil
}
// x25519KEM implements kemImplementation with X25519.
type x25519KEM struct {
privateKey [32]byte
setHighBit bool
}
func (e *x25519KEM) generate(rand io.Reader) (publicKey []byte, err error) {
_, err = io.ReadFull(rand, e.privateKey[:])
if err != nil {
return
}
var out [32]byte
curve25519.ScalarBaseMult(&out, &e.privateKey)
if e.setHighBit {
out[31] |= 0x80
}
return out[:], nil
}
func (e *x25519KEM) encap(rand io.Reader, peerKey []byte) (ciphertext []byte, secret []byte, err error) {
ciphertext, err = e.generate(rand)
if err != nil {
return nil, nil, err
}
secret, err = e.decap(peerKey)
if err != nil {
return nil, nil, err
}
return
}
func (e *x25519KEM) decap(ciphertext []byte) (secret []byte, err error) {
if len(ciphertext) != 32 {
return nil, errors.New("tls: invalid peer key")
}
var out [32]byte
curve25519.ScalarMult(&out, &e.privateKey, (*[32]byte)(ciphertext))
// Per RFC 7748, reject the all-zero value in constant time.
var zeros [32]byte
if subtle.ConstantTimeCompare(zeros[:], out[:]) == 1 {
return nil, errors.New("tls: X25519 value with wrong order")
}
return out[:], nil
}
// kyberKEM implements Kyber combined with X25519.
type kyberKEM struct {
x25519PrivateKey [32]byte
kyberPrivateKey *kyber.PrivateKey
}
func (e *kyberKEM) generate(rand io.Reader) (publicKey []byte, err error) {
if _, err := io.ReadFull(rand, e.x25519PrivateKey[:]); err != nil {
return nil, err
}
var x25519Public [32]byte
curve25519.ScalarBaseMult(&x25519Public, &e.x25519PrivateKey)
var kyberEntropy [64]byte
if _, err := io.ReadFull(rand, kyberEntropy[:]); err != nil {
return nil, err
}
var kyberPublic *[kyber.PublicKeySize]byte
e.kyberPrivateKey, kyberPublic = kyber.NewPrivateKey(&kyberEntropy)
var ret []byte
ret = append(ret, x25519Public[:]...)
ret = append(ret, kyberPublic[:]...)
return ret, nil
}
func (e *kyberKEM) encap(rand io.Reader, peerKey []byte) (ciphertext []byte, secret []byte, err error) {
if len(peerKey) != 32+kyber.PublicKeySize {
return nil, nil, errors.New("tls: bad length Kyber offer")
}
if _, err := io.ReadFull(rand, e.x25519PrivateKey[:]); err != nil {
return nil, nil, err
}
var x25519Shared, x25519PeerKey, x25519Public [32]byte
copy(x25519PeerKey[:], peerKey)
curve25519.ScalarBaseMult(&x25519Public, &e.x25519PrivateKey)
curve25519.ScalarMult(&x25519Shared, &e.x25519PrivateKey, &x25519PeerKey)
// Per RFC 7748, reject the all-zero value in constant time.
var zeros [32]byte
if subtle.ConstantTimeCompare(zeros[:], x25519Shared[:]) == 1 {
return nil, nil, errors.New("tls: X25519 value with wrong order")
}
kyberPublicKey, ok := kyber.UnmarshalPublicKey((*[kyber.PublicKeySize]byte)(peerKey[32:]))
if !ok {
return nil, nil, errors.New("tls: bad Kyber offer")
}
var kyberShared, kyberEntropy [32]byte
if _, err := io.ReadFull(rand, kyberEntropy[:]); err != nil {
return nil, nil, err
}
kyberCiphertext := kyberPublicKey.Encap(kyberShared[:], &kyberEntropy)
ciphertext = append(ciphertext, x25519Public[:]...)
ciphertext = append(ciphertext, kyberCiphertext[:]...)
secret = append(secret, x25519Shared[:]...)
secret = append(secret, kyberShared[:]...)
return ciphertext, secret, nil
}
func (e *kyberKEM) decap(ciphertext []byte) (secret []byte, err error) {
if len(ciphertext) != 32+kyber.CiphertextSize {
return nil, errors.New("tls: bad length Kyber reply")
}
var x25519Shared, x25519PeerKey [32]byte
copy(x25519PeerKey[:], ciphertext)
curve25519.ScalarMult(&x25519Shared, &e.x25519PrivateKey, &x25519PeerKey)
// Per RFC 7748, reject the all-zero value in constant time.
var zeros [32]byte
if subtle.ConstantTimeCompare(zeros[:], x25519Shared[:]) == 1 {
return nil, errors.New("tls: X25519 value with wrong order")
}
var kyberShared [32]byte
e.kyberPrivateKey.Decap(kyberShared[:], (*[kyber.CiphertextSize]byte)(ciphertext[32:]))
secret = append(secret, x25519Shared[:]...)
secret = append(secret, kyberShared[:]...)
return secret, nil
}
func kemForCurveID(id CurveID, config *Config) (kemImplementation, bool) {
switch id {
case CurveP224:
return &ecdhKEM{curve: elliptic.P224(), sendCompressed: config.Bugs.SendCompressedCoordinates}, true
case CurveP256:
return &ecdhKEM{curve: elliptic.P256(), sendCompressed: config.Bugs.SendCompressedCoordinates}, true
case CurveP384:
return &ecdhKEM{curve: elliptic.P384(), sendCompressed: config.Bugs.SendCompressedCoordinates}, true
case CurveP521:
return &ecdhKEM{curve: elliptic.P521(), sendCompressed: config.Bugs.SendCompressedCoordinates}, true
case CurveX25519:
return &x25519KEM{setHighBit: config.Bugs.SetX25519HighBit}, true
case CurveX25519Kyber768:
return &kyberKEM{}, true
default:
return nil, false
}
}
// keyAgreementAuthentication is a helper interface that specifies how
// to authenticate the ServerKeyExchange parameters.
type keyAgreementAuthentication interface {
signParameters(config *Config, cert *Credential, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error)
verifyParameters(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, key crypto.PublicKey, params []byte, sig []byte) error
}
// nilKeyAgreementAuthentication does not authenticate the key
// agreement parameters.
type nilKeyAgreementAuthentication struct{}
func (ka *nilKeyAgreementAuthentication) signParameters(config *Config, cert *Credential, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error) {
skx := new(serverKeyExchangeMsg)
skx.key = params
return skx, nil
}
func (ka *nilKeyAgreementAuthentication) verifyParameters(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, key crypto.PublicKey, params []byte, sig []byte) error {
return nil
}
// signedKeyAgreement signs the ServerKeyExchange parameters with the
// server's private key.
type signedKeyAgreement struct {
keyType keyType
version uint16
peerSignatureAlgorithm signatureAlgorithm
}
func (ka *signedKeyAgreement) signParameters(config *Config, cert *Credential, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error) {
// The message to be signed is prepended by the randoms.
var msg []byte
msg = append(msg, clientHello.random...)
msg = append(msg, hello.random...)
msg = append(msg, params...)
var sigAlg signatureAlgorithm
var err error
if ka.version >= VersionTLS12 {
sigAlg, err = selectSignatureAlgorithm(false /* server */, ka.version, cert, config, clientHello.signatureAlgorithms)
if err != nil {
return nil, err
}
}
sig, err := signMessage(false /* server */, ka.version, cert.PrivateKey, config, sigAlg, msg)
if err != nil {
return nil, err
}
if config.Bugs.SendSignatureAlgorithm != 0 {
sigAlg = config.Bugs.SendSignatureAlgorithm
}
skx := new(serverKeyExchangeMsg)
if config.Bugs.UnauthenticatedECDH {
skx.key = params
} else {
sigAlgsLen := 0
if ka.version >= VersionTLS12 {
sigAlgsLen = 2
}
skx.key = make([]byte, len(params)+sigAlgsLen+2+len(sig))
copy(skx.key, params)
k := skx.key[len(params):]
if ka.version >= VersionTLS12 {
k[0] = byte(sigAlg >> 8)
k[1] = byte(sigAlg)
k = k[2:]
}
k[0] = byte(len(sig) >> 8)
k[1] = byte(len(sig))
copy(k[2:], sig)
}
return skx, nil
}
func (ka *signedKeyAgreement) verifyParameters(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, publicKey crypto.PublicKey, params []byte, sig []byte) error {
// The peer's key must match the cipher type.
switch ka.keyType {
case keyTypeECDSA:
_, edsaOk := publicKey.(*ecdsa.PublicKey)
_, ed25519Ok := publicKey.(ed25519.PublicKey)
if !edsaOk && !ed25519Ok {
return errors.New("tls: ECDHE ECDSA requires a ECDSA or Ed25519 server public key")
}
case keyTypeRSA:
_, ok := publicKey.(*rsa.PublicKey)
if !ok {
return errors.New("tls: ECDHE RSA requires a RSA server public key")
}
default:
return errors.New("tls: unknown key type")
}
// The message to be signed is prepended by the randoms.
var msg []byte
msg = append(msg, clientHello.random...)
msg = append(msg, serverHello.random...)
msg = append(msg, params...)
var sigAlg signatureAlgorithm
if ka.version >= VersionTLS12 {
if len(sig) < 2 {
return errServerKeyExchange
}
sigAlg = signatureAlgorithm(sig[0])<<8 | signatureAlgorithm(sig[1])
sig = sig[2:]
// Stash the signature algorithm to be extracted by the handshake.
ka.peerSignatureAlgorithm = sigAlg
}
if len(sig) < 2 {
return errServerKeyExchange
}
sigLen := int(sig[0])<<8 | int(sig[1])
if sigLen+2 != len(sig) {
return errServerKeyExchange
}
sig = sig[2:]
return verifyMessage(true /* client */, ka.version, publicKey, config, sigAlg, msg, sig)
}
// ecdheKeyAgreement implements a TLS key agreement where the server
// generates a ephemeral EC public/private key pair and signs it. The
// pre-master secret is then calculated using ECDH. The signature may
// either be ECDSA or RSA.
type ecdheKeyAgreement struct {
auth keyAgreementAuthentication
kem kemImplementation
curveID CurveID
peerKey []byte
}
func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Credential, clientHello *clientHelloMsg, hello *serverHelloMsg, version uint16) (*serverKeyExchangeMsg, error) {
var curveid CurveID
preferredCurves := config.curvePreferences()
NextCandidate:
for _, candidate := range preferredCurves {
if isPqGroup(candidate) && version < VersionTLS13 {
// Post-quantum "groups" require TLS 1.3.
continue
}
for _, c := range clientHello.supportedCurves {
if candidate == c {
curveid = c
break NextCandidate
}
}
}
if curveid == 0 {
return nil, errors.New("tls: no supported elliptic curves offered")
}
var ok bool
if ka.kem, ok = kemForCurveID(curveid, config); !ok {
return nil, errors.New("tls: preferredCurves includes unsupported curve")
}
ka.curveID = curveid
publicKey, err := ka.kem.generate(config.rand())
if err != nil {
return nil, err
}
// http://tools.ietf.org/html/rfc4492#section-5.4
serverECDHParams := make([]byte, 1+2+1+len(publicKey))
serverECDHParams[0] = 3 // named curve
if config.Bugs.SendCurve != 0 {
curveid = config.Bugs.SendCurve
}
serverECDHParams[1] = byte(curveid >> 8)
serverECDHParams[2] = byte(curveid)
serverECDHParams[3] = byte(len(publicKey))
copy(serverECDHParams[4:], publicKey)
if config.Bugs.InvalidECDHPoint {
serverECDHParams[4] ^= 0xff
}
return ka.auth.signParameters(config, cert, clientHello, hello, serverECDHParams)
}
func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Credential, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
return nil, errClientKeyExchange
}
return ka.kem.decap(ckx.ciphertext[1:])
}
func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, key crypto.PublicKey, skx *serverKeyExchangeMsg) error {
if len(skx.key) < 4 {
return errServerKeyExchange
}
if skx.key[0] != 3 { // named curve
return errors.New("tls: server selected unsupported curve")
}
curveID := CurveID(skx.key[1])<<8 | CurveID(skx.key[2])
ka.curveID = curveID
var ok bool
if ka.kem, ok = kemForCurveID(curveID, config); !ok {
return errors.New("tls: server selected unsupported curve")
}
publicLen := int(skx.key[3])
if publicLen+4 > len(skx.key) {
return errServerKeyExchange
}
// Save the peer key for later.
ka.peerKey = skx.key[4 : 4+publicLen]
// Check the signature.
serverECDHParams := skx.key[:4+publicLen]
sig := skx.key[4+publicLen:]
return ka.auth.verifyParameters(config, clientHello, serverHello, key, serverECDHParams, sig)
}
func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
if ka.kem == nil {
return nil, nil, errors.New("missing ServerKeyExchange message")
}
ciphertext, secret, err := ka.kem.encap(config.rand(), ka.peerKey)
if err != nil {
return nil, nil, err
}
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, 1+len(ciphertext))
ckx.ciphertext[0] = byte(len(ciphertext))
copy(ckx.ciphertext[1:], ciphertext)
if config.Bugs.InvalidECDHPoint {
ckx.ciphertext[1] ^= 0xff
}
return secret, ckx, nil
}
func (ka *ecdheKeyAgreement) peerSignatureAlgorithm() signatureAlgorithm {
if auth, ok := ka.auth.(*signedKeyAgreement); ok {
return auth.peerSignatureAlgorithm
}
return 0
}
// nilKeyAgreement is a fake key agreement used to implement the plain PSK key
// exchange.
type nilKeyAgreement struct{}
func (ka *nilKeyAgreement) generateServerKeyExchange(config *Config, cert *Credential, clientHello *clientHelloMsg, hello *serverHelloMsg, version uint16) (*serverKeyExchangeMsg, error) {
return nil, nil
}
func (ka *nilKeyAgreement) processClientKeyExchange(config *Config, cert *Credential, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
if len(ckx.ciphertext) != 0 {
return nil, errClientKeyExchange
}
// Although in plain PSK, otherSecret is all zeros, the base key
// agreement does not access to the length of the pre-shared
// key. pskKeyAgreement instead interprets nil to mean to use all zeros
// of the appropriate length.
return nil, nil
}
func (ka *nilKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, key crypto.PublicKey, skx *serverKeyExchangeMsg) error {
if len(skx.key) != 0 {
return errServerKeyExchange
}
return nil
}
func (ka *nilKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
// Although in plain PSK, otherSecret is all zeros, the base key
// agreement does not access to the length of the pre-shared
// key. pskKeyAgreement instead interprets nil to mean to use all zeros
// of the appropriate length.
return nil, &clientKeyExchangeMsg{}, nil
}
func (ka *nilKeyAgreement) peerSignatureAlgorithm() signatureAlgorithm {
return 0
}
// makePSKPremaster formats a PSK pre-master secret based on otherSecret from
// the base key exchange and psk.
func makePSKPremaster(otherSecret, psk []byte) []byte {
out := make([]byte, 0, 2+len(otherSecret)+2+len(psk))
out = append(out, byte(len(otherSecret)>>8), byte(len(otherSecret)))
out = append(out, otherSecret...)
out = append(out, byte(len(psk)>>8), byte(len(psk)))
out = append(out, psk...)
return out
}
// pskKeyAgreement implements the PSK key agreement.
type pskKeyAgreement struct {
base keyAgreement
identityHint string
}
func (ka *pskKeyAgreement) generateServerKeyExchange(config *Config, cert *Credential, clientHello *clientHelloMsg, hello *serverHelloMsg, version uint16) (*serverKeyExchangeMsg, error) {
// Assemble the identity hint.
bytes := make([]byte, 2+len(config.PreSharedKeyIdentity))
bytes[0] = byte(len(config.PreSharedKeyIdentity) >> 8)
bytes[1] = byte(len(config.PreSharedKeyIdentity))
copy(bytes[2:], []byte(config.PreSharedKeyIdentity))
// If there is one, append the base key agreement's
// ServerKeyExchange.
baseSkx, err := ka.base.generateServerKeyExchange(config, cert, clientHello, hello, version)
if err != nil {
return nil, err
}
if baseSkx != nil {
bytes = append(bytes, baseSkx.key...)
} else if config.PreSharedKeyIdentity == "" && !config.Bugs.AlwaysSendPreSharedKeyIdentityHint {
// ServerKeyExchange is optional if the identity hint is empty
// and there would otherwise be no ServerKeyExchange.
return nil, nil
}
skx := new(serverKeyExchangeMsg)
skx.key = bytes
return skx, nil
}
func (ka *pskKeyAgreement) processClientKeyExchange(config *Config, cert *Credential, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
// First, process the PSK identity.
if len(ckx.ciphertext) < 2 {
return nil, errClientKeyExchange
}
identityLen := (int(ckx.ciphertext[0]) << 8) | int(ckx.ciphertext[1])
if 2+identityLen > len(ckx.ciphertext) {
return nil, errClientKeyExchange
}
identity := string(ckx.ciphertext[2 : 2+identityLen])
if identity != config.PreSharedKeyIdentity {
return nil, errors.New("tls: unexpected identity")
}
if config.PreSharedKey == nil {
return nil, errors.New("tls: pre-shared key not configured")
}
// Process the remainder of the ClientKeyExchange to compute the base
// pre-master secret.
newCkx := new(clientKeyExchangeMsg)
newCkx.ciphertext = ckx.ciphertext[2+identityLen:]
otherSecret, err := ka.base.processClientKeyExchange(config, cert, newCkx, version)
if err != nil {
return nil, err
}
if otherSecret == nil {
// Special-case for the plain PSK key exchanges.
otherSecret = make([]byte, len(config.PreSharedKey))
}
return makePSKPremaster(otherSecret, config.PreSharedKey), nil
}
func (ka *pskKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, key crypto.PublicKey, skx *serverKeyExchangeMsg) error {
if len(skx.key) < 2 {
return errServerKeyExchange
}
identityLen := (int(skx.key[0]) << 8) | int(skx.key[1])
if 2+identityLen > len(skx.key) {
return errServerKeyExchange
}
ka.identityHint = string(skx.key[2 : 2+identityLen])
// Process the remainder of the ServerKeyExchange.
newSkx := new(serverKeyExchangeMsg)
newSkx.key = skx.key[2+identityLen:]
return ka.base.processServerKeyExchange(config, clientHello, serverHello, key, newSkx)
}
func (ka *pskKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
// The server only sends an identity hint but, for purposes of
// test code, the server always sends the hint and it is
// required to match.
if ka.identityHint != config.PreSharedKeyIdentity {
return nil, nil, errors.New("tls: unexpected identity")
}
// Serialize the identity.
bytes := make([]byte, 2+len(config.PreSharedKeyIdentity))
bytes[0] = byte(len(config.PreSharedKeyIdentity) >> 8)
bytes[1] = byte(len(config.PreSharedKeyIdentity))
copy(bytes[2:], []byte(config.PreSharedKeyIdentity))
// Append the base key exchange's ClientKeyExchange.
otherSecret, baseCkx, err := ka.base.generateClientKeyExchange(config, clientHello, cert)
if err != nil {
return nil, nil, err
}
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = append(bytes, baseCkx.ciphertext...)
if config.PreSharedKey == nil {
return nil, nil, errors.New("tls: pre-shared key not configured")
}
if otherSecret == nil {
otherSecret = make([]byte, len(config.PreSharedKey))
}
return makePSKPremaster(otherSecret, config.PreSharedKey), ckx, nil
}
func (ka *pskKeyAgreement) peerSignatureAlgorithm() signatureAlgorithm {
return 0
}