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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/elliptic"
"crypto/md5"
"crypto/rand"
"crypto/rsa"
"crypto/sha1"
"crypto/x509"
"encoding/asn1"
"errors"
"fmt"
"io"
"math/big"
)
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 *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
// Save the client version for comparison later.
ka.clientVersion = versionToWire(clientHello.vers, clientHello.isDTLS)
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 tls12HashId uint8
if ka.version >= VersionTLS12 {
if tls12HashId, err = pickTLS12HashForSignature(signatureRSA, clientHello.signatureAndHashes, config.signatureAndHashesForServer()); err != nil {
return nil, err
}
}
digest, hashFunc, err := hashForServerKeyExchange(signatureRSA, tls12HashId, ka.version, clientHello.random, hello.random, serverRSAParams)
if err != nil {
return nil, err
}
privKey, ok := cert.PrivateKey.(*rsa.PrivateKey)
if !ok {
return nil, errors.New("RSA ephemeral key requires an RSA server private key")
}
sig, err := rsa.SignPKCS1v15(config.rand(), privKey, hashFunc, digest)
if err != nil {
return nil, errors.New("failed to sign RSA parameters: " + err.Error())
}
skx := new(serverKeyExchangeMsg)
sigAndHashLen := 0
if ka.version >= VersionTLS12 {
sigAndHashLen = 2
}
skx.key = make([]byte, len(serverRSAParams)+sigAndHashLen+2+len(sig))
copy(skx.key, serverRSAParams)
k := skx.key[len(serverRSAParams):]
if ka.version >= VersionTLS12 {
k[0] = tls12HashId
k[1] = signatureRSA
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 *Certificate, 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
}
ciphertext := ckx.ciphertext
if version != VersionSSL30 {
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, errors.New("tls: invalid version in RSA premaster")
}
return preMasterSecret, nil
}
func (ka *rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
return errors.New("tls: unexpected ServerKeyExchange")
}
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 == RSABadValueWrongVersion {
vers ^= 1
}
vers = versionToWire(vers, clientHello.isDTLS)
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, len(sentPreMasterSecret)+1)
copy(sentPreMasterSecret, preMasterSecret)
} else if bad == RSABadValueTooShort {
sentPreMasterSecret = sentPreMasterSecret[:len(sentPreMasterSecret)-1]
}
encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), sentPreMasterSecret)
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)
if clientHello.vers != VersionSSL30 {
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)
} else {
ckx.ciphertext = encrypted
}
return preMasterSecret, ckx, nil
}
// sha1Hash calculates a SHA1 hash over the given byte slices.
func sha1Hash(slices [][]byte) []byte {
hsha1 := sha1.New()
for _, slice := range slices {
hsha1.Write(slice)
}
return hsha1.Sum(nil)
}
// md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the
// concatenation of an MD5 and SHA1 hash.
func md5SHA1Hash(slices [][]byte) []byte {
md5sha1 := make([]byte, md5.Size+sha1.Size)
hmd5 := md5.New()
for _, slice := range slices {
hmd5.Write(slice)
}
copy(md5sha1, hmd5.Sum(nil))
copy(md5sha1[md5.Size:], sha1Hash(slices))
return md5sha1
}
// hashForServerKeyExchange hashes the given slices and returns their digest
// and the identifier of the hash function used. The hashFunc argument is only
// used for >= TLS 1.2 and precisely identifies the hash function to use.
func hashForServerKeyExchange(sigType, hashFunc uint8, version uint16, slices ...[]byte) ([]byte, crypto.Hash, error) {
if version >= VersionTLS12 {
hash, err := lookupTLSHash(hashFunc)
if err != nil {
return nil, 0, err
}
h := hash.New()
for _, slice := range slices {
h.Write(slice)
}
return h.Sum(nil), hash, nil
}
if sigType == signatureECDSA {
return sha1Hash(slices), crypto.SHA1, nil
}
return md5SHA1Hash(slices), crypto.MD5SHA1, nil
}
// pickTLS12HashForSignature returns a TLS 1.2 hash identifier for signing a
// ServerKeyExchange given the signature type being used and the client's
// advertized list of supported signature and hash combinations.
func pickTLS12HashForSignature(sigType uint8, clientList, serverList []signatureAndHash) (uint8, error) {
if len(clientList) == 0 {
// If the client didn't specify any signature_algorithms
// extension then we can assume that it supports SHA1. See
// http://tools.ietf.org/html/rfc5246#section-7.4.1.4.1
return hashSHA1, nil
}
for _, sigAndHash := range clientList {
if sigAndHash.signature != sigType {
continue
}
if isSupportedSignatureAndHash(sigAndHash, serverList) {
return sigAndHash.hash, nil
}
}
return 0, errors.New("tls: client doesn't support any common hash functions")
}
func curveForCurveID(id CurveID) (elliptic.Curve, bool) {
switch id {
case CurveP224:
return elliptic.P224(), true
case CurveP256:
return elliptic.P256(), true
case CurveP384:
return elliptic.P384(), true
case CurveP521:
return elliptic.P521(), 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 *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error)
verifyParameters(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, params []byte, sig []byte) error
}
// nilKeyAgreementAuthentication does not authenticate the key
// agreement parameters.
type nilKeyAgreementAuthentication struct{}
func (ka *nilKeyAgreementAuthentication) signParameters(config *Config, cert *Certificate, 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, cert *x509.Certificate, params []byte, sig []byte) error {
return nil
}
// signedKeyAgreement signs the ServerKeyExchange parameters with the
// server's private key.
type signedKeyAgreement struct {
version uint16
sigType uint8
}
func (ka *signedKeyAgreement) signParameters(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error) {
var tls12HashId uint8
var err error
if ka.version >= VersionTLS12 {
if tls12HashId, err = pickTLS12HashForSignature(ka.sigType, clientHello.signatureAndHashes, config.signatureAndHashesForServer()); err != nil {
return nil, err
}
}
digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, tls12HashId, ka.version, clientHello.random, hello.random, params)
if err != nil {
return nil, err
}
if config.Bugs.InvalidSKXSignature {
digest[0] ^= 0x80
}
var sig []byte
switch ka.sigType {
case signatureECDSA:
privKey, ok := cert.PrivateKey.(*ecdsa.PrivateKey)
if !ok {
return nil, errors.New("ECDHE ECDSA requires an ECDSA server private key")
}
r, s, err := ecdsa.Sign(config.rand(), privKey, digest)
if err != nil {
return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
}
order := privKey.Curve.Params().N
r = maybeCorruptECDSAValue(r, config.Bugs.BadECDSAR, order)
s = maybeCorruptECDSAValue(s, config.Bugs.BadECDSAS, order)
sig, err = asn1.Marshal(ecdsaSignature{r, s})
case signatureRSA:
privKey, ok := cert.PrivateKey.(*rsa.PrivateKey)
if !ok {
return nil, errors.New("ECDHE RSA requires a RSA server private key")
}
sig, err = rsa.SignPKCS1v15(config.rand(), privKey, hashFunc, digest)
if err != nil {
return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
}
default:
return nil, errors.New("unknown ECDHE signature algorithm")
}
skx := new(serverKeyExchangeMsg)
if config.Bugs.UnauthenticatedECDH {
skx.key = params
} else {
sigAndHashLen := 0
if ka.version >= VersionTLS12 {
sigAndHashLen = 2
}
skx.key = make([]byte, len(params)+sigAndHashLen+2+len(sig))
copy(skx.key, params)
k := skx.key[len(params):]
if ka.version >= VersionTLS12 {
k[0] = tls12HashId
k[1] = ka.sigType
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, cert *x509.Certificate, params []byte, sig []byte) error {
if len(sig) < 2 {
return errServerKeyExchange
}
var tls12HashId uint8
if ka.version >= VersionTLS12 {
// handle SignatureAndHashAlgorithm
var sigAndHash []uint8
sigAndHash, sig = sig[:2], sig[2:]
if sigAndHash[1] != ka.sigType {
return errServerKeyExchange
}
tls12HashId = sigAndHash[0]
if len(sig) < 2 {
return errServerKeyExchange
}
if !isSupportedSignatureAndHash(signatureAndHash{ka.sigType, tls12HashId}, config.signatureAndHashesForClient()) {
return errors.New("tls: unsupported hash function for ServerKeyExchange")
}
}
sigLen := int(sig[0])<<8 | int(sig[1])
if sigLen+2 != len(sig) {
return errServerKeyExchange
}
sig = sig[2:]
digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, tls12HashId, ka.version, clientHello.random, serverHello.random, params)
if err != nil {
return err
}
switch ka.sigType {
case signatureECDSA:
pubKey, ok := cert.PublicKey.(*ecdsa.PublicKey)
if !ok {
return errors.New("ECDHE ECDSA requires a ECDSA server public key")
}
ecdsaSig := new(ecdsaSignature)
if _, err := asn1.Unmarshal(sig, ecdsaSig); err != nil {
return err
}
if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
return errors.New("ECDSA signature contained zero or negative values")
}
if !ecdsa.Verify(pubKey, digest, ecdsaSig.R, ecdsaSig.S) {
return errors.New("ECDSA verification failure")
}
case signatureRSA:
pubKey, ok := cert.PublicKey.(*rsa.PublicKey)
if !ok {
return errors.New("ECDHE RSA requires a RSA server public key")
}
if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, digest, sig); err != nil {
return err
}
default:
return errors.New("unknown ECDHE signature algorithm")
}
return nil
}
// ecdheRSAKeyAgreement 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
privateKey []byte
curve elliptic.Curve
x, y *big.Int
}
func maybeCorruptECDSAValue(n *big.Int, typeOfCorruption BadValue, limit *big.Int) *big.Int {
switch typeOfCorruption {
case BadValueNone:
return n
case BadValueNegative:
return new(big.Int).Neg(n)
case BadValueZero:
return big.NewInt(0)
case BadValueLimit:
return limit
case BadValueLarge:
bad := new(big.Int).Set(limit)
return bad.Lsh(bad, 20)
default:
panic("unknown BadValue type")
}
}
func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
var curveid CurveID
preferredCurves := config.curvePreferences()
NextCandidate:
for _, candidate := range preferredCurves {
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.curve, ok = curveForCurveID(curveid); !ok {
return nil, errors.New("tls: preferredCurves includes unsupported curve")
}
var x, y *big.Int
var err error
ka.privateKey, x, y, err = elliptic.GenerateKey(ka.curve, config.rand())
if err != nil {
return nil, err
}
ecdhePublic := elliptic.Marshal(ka.curve, x, y)
// http://tools.ietf.org/html/rfc4492#section-5.4
serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
serverECDHParams[0] = 3 // named curve
serverECDHParams[1] = byte(curveid >> 8)
serverECDHParams[2] = byte(curveid)
if config.Bugs.InvalidSKXCurve {
serverECDHParams[2] ^= 0xff
}
serverECDHParams[3] = byte(len(ecdhePublic))
copy(serverECDHParams[4:], ecdhePublic)
return ka.auth.signParameters(config, cert, clientHello, hello, serverECDHParams)
}
func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
return nil, errClientKeyExchange
}
x, y := elliptic.Unmarshal(ka.curve, ckx.ciphertext[1:])
if x == nil {
return nil, errClientKeyExchange
}
x, _ = ka.curve.ScalarMult(x, y, ka.privateKey)
preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
return preMasterSecret, nil
}
func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, 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])
var ok bool
if ka.curve, ok = curveForCurveID(curveid); !ok {
return errors.New("tls: server selected unsupported curve")
}
publicLen := int(skx.key[3])
if publicLen+4 > len(skx.key) {
return errServerKeyExchange
}
ka.x, ka.y = elliptic.Unmarshal(ka.curve, skx.key[4:4+publicLen])
if ka.x == nil {
return errServerKeyExchange
}
serverECDHParams := skx.key[:4+publicLen]
sig := skx.key[4+publicLen:]
return ka.auth.verifyParameters(config, clientHello, serverHello, cert, serverECDHParams, sig)
}
func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
if ka.curve == nil {
return nil, nil, errors.New("missing ServerKeyExchange message")
}
priv, mx, my, err := elliptic.GenerateKey(ka.curve, config.rand())
if err != nil {
return nil, nil, err
}
x, _ := ka.curve.ScalarMult(ka.x, ka.y, priv)
preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
serialized := elliptic.Marshal(ka.curve, mx, my)
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, 1+len(serialized))
ckx.ciphertext[0] = byte(len(serialized))
copy(ckx.ciphertext[1:], serialized)
return preMasterSecret, ckx, nil
}
// dheRSAKeyAgreement implements a TLS key agreement where the server generates
// an ephemeral Diffie-Hellman public/private key pair and signs it. The
// pre-master secret is then calculated using Diffie-Hellman.
type dheKeyAgreement struct {
auth keyAgreementAuthentication
p, g *big.Int
yTheirs *big.Int
xOurs *big.Int
}
func (ka *dheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
var q *big.Int
if p := config.Bugs.DHGroupPrime; p != nil {
ka.p = p
ka.g = big.NewInt(2)
q = p
} else {
// 2048-bit MODP Group with 256-bit Prime Order Subgroup (RFC
// 5114, Section 2.3)
ka.p, _ = new(big.Int).SetString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
ka.g, _ = new(big.Int).SetString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
q, _ = new(big.Int).SetString("8CF83642A709A097B447997640129DA299B1A47D1EB3750BA308B0FE64F5FBD3", 16)
}
var err error
ka.xOurs, err = rand.Int(config.rand(), q)
if err != nil {
return nil, err
}
yOurs := new(big.Int).Exp(ka.g, ka.xOurs, ka.p)
// http://tools.ietf.org/html/rfc5246#section-7.4.3
pBytes := ka.p.Bytes()
gBytes := ka.g.Bytes()
yBytes := yOurs.Bytes()
serverDHParams := make([]byte, 0, 2+len(pBytes)+2+len(gBytes)+2+len(yBytes))
serverDHParams = append(serverDHParams, byte(len(pBytes)>>8), byte(len(pBytes)))
serverDHParams = append(serverDHParams, pBytes...)
serverDHParams = append(serverDHParams, byte(len(gBytes)>>8), byte(len(gBytes)))
serverDHParams = append(serverDHParams, gBytes...)
serverDHParams = append(serverDHParams, byte(len(yBytes)>>8), byte(len(yBytes)))
serverDHParams = append(serverDHParams, yBytes...)
return ka.auth.signParameters(config, cert, clientHello, hello, serverDHParams)
}
func (ka *dheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
if len(ckx.ciphertext) < 2 {
return nil, errClientKeyExchange
}
yLen := (int(ckx.ciphertext[0]) << 8) | int(ckx.ciphertext[1])
if yLen != len(ckx.ciphertext)-2 {
return nil, errClientKeyExchange
}
yTheirs := new(big.Int).SetBytes(ckx.ciphertext[2:])
if yTheirs.Sign() <= 0 || yTheirs.Cmp(ka.p) >= 0 {
return nil, errClientKeyExchange
}
return new(big.Int).Exp(yTheirs, ka.xOurs, ka.p).Bytes(), nil
}
func (ka *dheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
// Read dh_p
k := skx.key
if len(k) < 2 {
return errServerKeyExchange
}
pLen := (int(k[0]) << 8) | int(k[1])
k = k[2:]
if len(k) < pLen {
return errServerKeyExchange
}
ka.p = new(big.Int).SetBytes(k[:pLen])
k = k[pLen:]
// Read dh_g
if len(k) < 2 {
return errServerKeyExchange
}
gLen := (int(k[0]) << 8) | int(k[1])
k = k[2:]
if len(k) < gLen {
return errServerKeyExchange
}
ka.g = new(big.Int).SetBytes(k[:gLen])
k = k[gLen:]
// Read dh_Ys
if len(k) < 2 {
return errServerKeyExchange
}
yLen := (int(k[0]) << 8) | int(k[1])
k = k[2:]
if len(k) < yLen {
return errServerKeyExchange
}
ka.yTheirs = new(big.Int).SetBytes(k[:yLen])
k = k[yLen:]
if ka.yTheirs.Sign() <= 0 || ka.yTheirs.Cmp(ka.p) >= 0 {
return errServerKeyExchange
}
if l := config.Bugs.RequireDHPublicValueLen; l != 0 && l != yLen {
return fmt.Errorf("RequireDHPublicValueLen set to %d, but server's public value was %d bytes on the wire and %d bytes if minimal", l, yLen, (ka.yTheirs.BitLen()+7)/8)
}
sig := k
serverDHParams := skx.key[:len(skx.key)-len(sig)]
return ka.auth.verifyParameters(config, clientHello, serverHello, cert, serverDHParams, sig)
}
func (ka *dheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
if ka.p == nil || ka.g == nil || ka.yTheirs == nil {
return nil, nil, errors.New("missing ServerKeyExchange message")
}
xOurs, err := rand.Int(config.rand(), ka.p)
if err != nil {
return nil, nil, err
}
preMasterSecret := new(big.Int).Exp(ka.yTheirs, xOurs, ka.p).Bytes()
yOurs := new(big.Int).Exp(ka.g, xOurs, ka.p)
yBytes := yOurs.Bytes()
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, 2+len(yBytes))
ckx.ciphertext[0] = byte(len(yBytes) >> 8)
ckx.ciphertext[1] = byte(len(yBytes))
copy(ckx.ciphertext[2:], yBytes)
return preMasterSecret, ckx, nil
}
// nilKeyAgreement is a fake key agreement used to implement the plain PSK key
// exchange.
type nilKeyAgreement struct{}
func (ka *nilKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
return nil, nil
}
func (ka *nilKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, 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, cert *x509.Certificate, 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
}
// 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 *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*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)
if err != nil {
return nil, err
}
if baseSkx != nil {
bytes = append(bytes, baseSkx.key...)
} else if config.PreSharedKeyIdentity == "" {
// 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 *Certificate, 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, cert *x509.Certificate, 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, cert, 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
}