9f46cf9e2d
This adds support for RSASSA-PSS signatures in handshake messages as required by TLS 1.3. Even if TLS 1.2 is negotiated, it must support PSS when advertised in the Client Hello (this will be done later as the testdata will change). Updates #9671 Change-Id: I8006b92e017453ae408c153233ce5ccef99b5c3f
404 lines
12 KiB
Go
404 lines
12 KiB
Go
// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package tls
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import (
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"crypto"
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"crypto/elliptic"
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"crypto/md5"
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"crypto/rsa"
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"crypto/sha1"
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"crypto/x509"
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"errors"
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"io"
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"math/big"
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"golang_org/x/crypto/curve25519"
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)
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var errClientKeyExchange = errors.New("tls: invalid ClientKeyExchange message")
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var errServerKeyExchange = errors.New("tls: invalid ServerKeyExchange message")
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// rsaKeyAgreement implements the standard TLS key agreement where the client
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// encrypts the pre-master secret to the server's public key.
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type rsaKeyAgreement struct{}
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func (ka rsaKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
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return nil, nil
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}
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func (ka rsaKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
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if len(ckx.ciphertext) < 2 {
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return nil, errClientKeyExchange
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}
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ciphertext := ckx.ciphertext
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if version != VersionSSL30 {
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ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1])
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if ciphertextLen != len(ckx.ciphertext)-2 {
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return nil, errClientKeyExchange
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}
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ciphertext = ckx.ciphertext[2:]
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}
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priv, ok := cert.PrivateKey.(crypto.Decrypter)
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if !ok {
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return nil, errors.New("tls: certificate private key does not implement crypto.Decrypter")
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}
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// Perform constant time RSA PKCS#1 v1.5 decryption
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preMasterSecret, err := priv.Decrypt(config.rand(), ciphertext, &rsa.PKCS1v15DecryptOptions{SessionKeyLen: 48})
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if err != nil {
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return nil, err
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}
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// We don't check the version number in the premaster secret. For one,
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// by checking it, we would leak information about the validity of the
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// encrypted pre-master secret. Secondly, it provides only a small
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// benefit against a downgrade attack and some implementations send the
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// wrong version anyway. See the discussion at the end of section
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// 7.4.7.1 of RFC 4346.
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return preMasterSecret, nil
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}
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func (ka rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
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return errors.New("tls: unexpected ServerKeyExchange")
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}
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func (ka rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
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preMasterSecret := make([]byte, 48)
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preMasterSecret[0] = byte(clientHello.vers >> 8)
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preMasterSecret[1] = byte(clientHello.vers)
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_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
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if err != nil {
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return nil, nil, err
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}
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encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), preMasterSecret)
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if err != nil {
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return nil, nil, err
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}
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ckx := new(clientKeyExchangeMsg)
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ckx.ciphertext = make([]byte, len(encrypted)+2)
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ckx.ciphertext[0] = byte(len(encrypted) >> 8)
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ckx.ciphertext[1] = byte(len(encrypted))
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copy(ckx.ciphertext[2:], encrypted)
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return preMasterSecret, ckx, nil
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}
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// sha1Hash calculates a SHA1 hash over the given byte slices.
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func sha1Hash(slices [][]byte) []byte {
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hsha1 := sha1.New()
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for _, slice := range slices {
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hsha1.Write(slice)
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}
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return hsha1.Sum(nil)
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}
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// md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the
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// concatenation of an MD5 and SHA1 hash.
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func md5SHA1Hash(slices [][]byte) []byte {
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md5sha1 := make([]byte, md5.Size+sha1.Size)
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hmd5 := md5.New()
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for _, slice := range slices {
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hmd5.Write(slice)
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}
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copy(md5sha1, hmd5.Sum(nil))
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copy(md5sha1[md5.Size:], sha1Hash(slices))
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return md5sha1
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}
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// hashForServerKeyExchange hashes the given slices and returns their digest
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// using the given hash function.
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func hashForServerKeyExchange(sigType uint8, hashFunc crypto.Hash, version uint16, slices ...[]byte) ([]byte, error) {
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if version >= VersionTLS12 {
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h := hashFunc.New()
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for _, slice := range slices {
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h.Write(slice)
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}
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digest := h.Sum(nil)
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return digest, nil
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}
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if sigType == signatureECDSA {
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return sha1Hash(slices), nil
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}
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return md5SHA1Hash(slices), nil
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}
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func curveForCurveID(id CurveID) (elliptic.Curve, bool) {
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switch id {
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case CurveP256:
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return elliptic.P256(), true
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case CurveP384:
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return elliptic.P384(), true
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case CurveP521:
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return elliptic.P521(), true
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default:
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return nil, false
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}
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}
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// ecdheKeyAgreement implements a TLS key agreement where the server
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// generates an ephemeral EC public/private key pair and signs it. The
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// pre-master secret is then calculated using ECDH. The signature may
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// either be ECDSA or RSA.
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type ecdheKeyAgreement struct {
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version uint16
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isRSA bool
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privateKey []byte
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curveid CurveID
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// publicKey is used to store the peer's public value when X25519 is
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// being used.
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publicKey []byte
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// x and y are used to store the peer's public value when one of the
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// NIST curves is being used.
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x, y *big.Int
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}
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func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
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preferredCurves := config.curvePreferences()
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NextCandidate:
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for _, candidate := range preferredCurves {
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for _, c := range clientHello.supportedCurves {
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if candidate == c {
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ka.curveid = c
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break NextCandidate
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}
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}
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}
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if ka.curveid == 0 {
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return nil, errors.New("tls: no supported elliptic curves offered")
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}
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var ecdhePublic []byte
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if ka.curveid == X25519 {
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var scalar, public [32]byte
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if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil {
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return nil, err
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}
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curve25519.ScalarBaseMult(&public, &scalar)
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ka.privateKey = scalar[:]
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ecdhePublic = public[:]
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} else {
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curve, ok := curveForCurveID(ka.curveid)
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if !ok {
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return nil, errors.New("tls: preferredCurves includes unsupported curve")
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}
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var x, y *big.Int
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var err error
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ka.privateKey, x, y, err = elliptic.GenerateKey(curve, config.rand())
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if err != nil {
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return nil, err
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}
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ecdhePublic = elliptic.Marshal(curve, x, y)
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}
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// http://tools.ietf.org/html/rfc4492#section-5.4
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serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
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serverECDHParams[0] = 3 // named curve
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serverECDHParams[1] = byte(ka.curveid >> 8)
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serverECDHParams[2] = byte(ka.curveid)
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serverECDHParams[3] = byte(len(ecdhePublic))
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copy(serverECDHParams[4:], ecdhePublic)
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priv, ok := cert.PrivateKey.(crypto.Signer)
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if !ok {
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return nil, errors.New("tls: certificate private key does not implement crypto.Signer")
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}
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signatureAlgorithm, sigType, hashFunc, err := pickSignatureAlgorithm(priv.Public(), clientHello.supportedSignatureAlgorithms, supportedSignatureAlgorithms, ka.version)
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if err != nil {
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return nil, err
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}
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if (sigType == signaturePKCS1v15 || sigType == signatureRSAPSS) != ka.isRSA {
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return nil, errors.New("tls: certificate cannot be used with the selected cipher suite")
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}
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digest, err := hashForServerKeyExchange(sigType, hashFunc, ka.version, clientHello.random, hello.random, serverECDHParams)
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if err != nil {
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return nil, err
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}
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var sig []byte
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signOpts := crypto.SignerOpts(hashFunc)
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if sigType == signatureRSAPSS {
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signOpts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: hashFunc}
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}
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sig, err = priv.Sign(config.rand(), digest, signOpts)
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if err != nil {
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return nil, errors.New("tls: failed to sign ECDHE parameters: " + err.Error())
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}
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skx := new(serverKeyExchangeMsg)
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sigAndHashLen := 0
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if ka.version >= VersionTLS12 {
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sigAndHashLen = 2
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}
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skx.key = make([]byte, len(serverECDHParams)+sigAndHashLen+2+len(sig))
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copy(skx.key, serverECDHParams)
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k := skx.key[len(serverECDHParams):]
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if ka.version >= VersionTLS12 {
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k[0] = byte(signatureAlgorithm >> 8)
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k[1] = byte(signatureAlgorithm)
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k = k[2:]
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}
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k[0] = byte(len(sig) >> 8)
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k[1] = byte(len(sig))
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copy(k[2:], sig)
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return skx, nil
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}
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func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
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if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
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return nil, errClientKeyExchange
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}
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if ka.curveid == X25519 {
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if len(ckx.ciphertext) != 1+32 {
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return nil, errClientKeyExchange
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}
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var theirPublic, sharedKey, scalar [32]byte
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copy(theirPublic[:], ckx.ciphertext[1:])
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copy(scalar[:], ka.privateKey)
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curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic)
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return sharedKey[:], nil
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}
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curve, ok := curveForCurveID(ka.curveid)
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if !ok {
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panic("internal error")
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}
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x, y := elliptic.Unmarshal(curve, ckx.ciphertext[1:]) // Unmarshal also checks whether the given point is on the curve
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if x == nil {
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return nil, errClientKeyExchange
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}
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x, _ = curve.ScalarMult(x, y, ka.privateKey)
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curveSize := (curve.Params().BitSize + 7) >> 3
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xBytes := x.Bytes()
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if len(xBytes) == curveSize {
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return xBytes, nil
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}
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preMasterSecret := make([]byte, curveSize)
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copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
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return preMasterSecret, nil
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}
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func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
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if len(skx.key) < 4 {
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return errServerKeyExchange
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}
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if skx.key[0] != 3 { // named curve
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return errors.New("tls: server selected unsupported curve")
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}
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ka.curveid = CurveID(skx.key[1])<<8 | CurveID(skx.key[2])
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publicLen := int(skx.key[3])
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if publicLen+4 > len(skx.key) {
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return errServerKeyExchange
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}
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serverECDHParams := skx.key[:4+publicLen]
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publicKey := serverECDHParams[4:]
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sig := skx.key[4+publicLen:]
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if len(sig) < 2 {
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return errServerKeyExchange
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}
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if ka.curveid == X25519 {
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if len(publicKey) != 32 {
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return errors.New("tls: bad X25519 public value")
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}
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ka.publicKey = publicKey
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} else {
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curve, ok := curveForCurveID(ka.curveid)
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if !ok {
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return errors.New("tls: server selected unsupported curve")
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}
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ka.x, ka.y = elliptic.Unmarshal(curve, publicKey) // Unmarshal also checks whether the given point is on the curve
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if ka.x == nil {
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return errServerKeyExchange
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}
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}
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var signatureAlgorithm SignatureScheme
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if ka.version >= VersionTLS12 {
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// handle SignatureAndHashAlgorithm
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signatureAlgorithm = SignatureScheme(sig[0])<<8 | SignatureScheme(sig[1])
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sig = sig[2:]
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if len(sig) < 2 {
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return errServerKeyExchange
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}
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}
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_, sigType, hashFunc, err := pickSignatureAlgorithm(cert.PublicKey, []SignatureScheme{signatureAlgorithm}, clientHello.supportedSignatureAlgorithms, ka.version)
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if err != nil {
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return err
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}
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if (sigType == signaturePKCS1v15 || sigType == signatureRSAPSS) != ka.isRSA {
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return errServerKeyExchange
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}
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sigLen := int(sig[0])<<8 | int(sig[1])
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if sigLen+2 != len(sig) {
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return errServerKeyExchange
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}
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sig = sig[2:]
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digest, err := hashForServerKeyExchange(sigType, hashFunc, ka.version, clientHello.random, serverHello.random, serverECDHParams)
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if err != nil {
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return err
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}
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return verifyHandshakeSignature(sigType, cert.PublicKey, hashFunc, digest, sig)
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}
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func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
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if ka.curveid == 0 {
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return nil, nil, errors.New("tls: missing ServerKeyExchange message")
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}
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var serialized, preMasterSecret []byte
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if ka.curveid == X25519 {
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var ourPublic, theirPublic, sharedKey, scalar [32]byte
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if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil {
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return nil, nil, err
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}
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copy(theirPublic[:], ka.publicKey)
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curve25519.ScalarBaseMult(&ourPublic, &scalar)
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curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic)
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serialized = ourPublic[:]
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preMasterSecret = sharedKey[:]
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} else {
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curve, ok := curveForCurveID(ka.curveid)
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if !ok {
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panic("internal error")
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}
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priv, mx, my, err := elliptic.GenerateKey(curve, config.rand())
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if err != nil {
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return nil, nil, err
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}
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x, _ := curve.ScalarMult(ka.x, ka.y, priv)
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preMasterSecret = make([]byte, (curve.Params().BitSize+7)>>3)
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xBytes := x.Bytes()
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copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
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serialized = elliptic.Marshal(curve, mx, my)
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}
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ckx := new(clientKeyExchangeMsg)
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ckx.ciphertext = make([]byte, 1+len(serialized))
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ckx.ciphertext[0] = byte(len(serialized))
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copy(ckx.ciphertext[1:], serialized)
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return preMasterSecret, ckx, nil
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}
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