357 lines
12 KiB
Go
357 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/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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"fmt"
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"io"
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)
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// a keyAgreement implements the client and server side of a TLS key agreement
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// protocol by generating and processing key exchange messages.
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type keyAgreement interface {
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// On the server side, the first two methods are called in order.
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// In the case that the key agreement protocol doesn't use a
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// ServerKeyExchange message, generateServerKeyExchange can return nil,
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// nil.
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generateServerKeyExchange(*Config, *Certificate, *clientHelloMsg, *serverHelloMsg) (*serverKeyExchangeMsg, error)
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processClientKeyExchange(*Config, *Certificate, *clientKeyExchangeMsg, uint16) ([]byte, error)
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// On the client side, the next two methods are called in order.
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// This method may not be called if the server doesn't send a
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// ServerKeyExchange message.
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processServerKeyExchange(*Config, *clientHelloMsg, *serverHelloMsg, *x509.Certificate, *serverKeyExchangeMsg) error
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generateClientKeyExchange(*Config, *clientHelloMsg, *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error)
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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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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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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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rsaKey, ok := cert.PublicKey.(*rsa.PublicKey)
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if !ok {
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return nil, nil, errors.New("tls: server certificate contains incorrect key type for selected ciphersuite")
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}
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encrypted, err := rsa.EncryptPKCS1v15(config.rand(), rsaKey, 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 (for >= TLS 1.2) or using a default based on
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// the sigType (for earlier TLS versions). For Ed25519 signatures, which don't
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// do pre-hashing, it returns the concatenation of the slices.
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func hashForServerKeyExchange(sigType uint8, hashFunc crypto.Hash, version uint16, slices ...[]byte) []byte {
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if sigType == signatureEd25519 {
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var signed []byte
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for _, slice := range slices {
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signed = append(signed, slice...)
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}
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return signed
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}
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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
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}
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if sigType == signatureECDSA {
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return sha1Hash(slices)
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}
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return md5SHA1Hash(slices)
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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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// be ECDSA, Ed25519 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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params ecdheParameters
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// ckx and preMasterSecret are generated in processServerKeyExchange
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// and returned in generateClientKeyExchange.
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ckx *clientKeyExchangeMsg
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preMasterSecret []byte
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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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var curveID CurveID
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for _, c := range clientHello.supportedCurves {
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if config.supportsCurve(c) {
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curveID = c
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break
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}
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}
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if curveID == 0 {
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return nil, errors.New("tls: no supported elliptic curves offered")
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}
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if _, ok := curveForCurveID(curveID); curveID != X25519 && !ok {
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return nil, errors.New("tls: CurvePreferences includes unsupported curve")
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}
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params, err := generateECDHEParameters(config.rand(), curveID)
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if err != nil {
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return nil, err
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}
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ka.params = params
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// See RFC 4492, Section 5.4.
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ecdhePublic := params.PublicKey()
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serverECDHEParams := make([]byte, 1+2+1+len(ecdhePublic))
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serverECDHEParams[0] = 3 // named curve
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serverECDHEParams[1] = byte(curveID >> 8)
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serverECDHEParams[2] = byte(curveID)
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serverECDHEParams[3] = byte(len(ecdhePublic))
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copy(serverECDHEParams[4:], ecdhePublic)
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priv, ok := cert.PrivateKey.(crypto.Signer)
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if !ok {
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return nil, fmt.Errorf("tls: certificate private key of type %T does not implement crypto.Signer", cert.PrivateKey)
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}
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var signatureAlgorithm SignatureScheme
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var sigType uint8
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var sigHash crypto.Hash
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if ka.version >= VersionTLS12 {
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signatureAlgorithm, err = selectSignatureScheme(ka.version, cert, clientHello.supportedSignatureAlgorithms)
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if err != nil {
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return nil, err
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}
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sigType, sigHash, err = typeAndHashFromSignatureScheme(signatureAlgorithm)
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if err != nil {
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return nil, err
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}
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} else {
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sigType, sigHash, err = legacyTypeAndHashFromPublicKey(priv.Public())
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if err != nil {
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return nil, err
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}
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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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signed := hashForServerKeyExchange(sigType, sigHash, ka.version, clientHello.random, hello.random, serverECDHEParams)
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signOpts := crypto.SignerOpts(sigHash)
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if sigType == signatureRSAPSS {
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signOpts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: sigHash}
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}
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sig, err := priv.Sign(config.rand(), signed, 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(serverECDHEParams)+sigAndHashLen+2+len(sig))
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copy(skx.key, serverECDHEParams)
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k := skx.key[len(serverECDHEParams):]
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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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preMasterSecret := ka.params.SharedKey(ckx.ciphertext[1:])
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if preMasterSecret == nil {
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return nil, errClientKeyExchange
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}
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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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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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serverECDHEParams := skx.key[:4+publicLen]
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publicKey := serverECDHEParams[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 _, ok := curveForCurveID(curveID); curveID != X25519 && !ok {
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return errors.New("tls: server selected unsupported curve")
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}
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params, err := generateECDHEParameters(config.rand(), curveID)
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if err != nil {
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return err
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}
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ka.params = params
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ka.preMasterSecret = params.SharedKey(publicKey)
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if ka.preMasterSecret == nil {
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return errServerKeyExchange
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}
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ourPublicKey := params.PublicKey()
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ka.ckx = new(clientKeyExchangeMsg)
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ka.ckx.ciphertext = make([]byte, 1+len(ourPublicKey))
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ka.ckx.ciphertext[0] = byte(len(ourPublicKey))
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copy(ka.ckx.ciphertext[1:], ourPublicKey)
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var sigType uint8
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var sigHash crypto.Hash
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if ka.version >= VersionTLS12 {
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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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if !isSupportedSignatureAlgorithm(signatureAlgorithm, clientHello.supportedSignatureAlgorithms) {
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return errors.New("tls: certificate used with invalid signature algorithm")
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}
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sigType, sigHash, err = typeAndHashFromSignatureScheme(signatureAlgorithm)
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if err != nil {
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return err
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}
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} else {
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sigType, sigHash, err = legacyTypeAndHashFromPublicKey(cert.PublicKey)
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if err != nil {
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return err
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}
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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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signed := hashForServerKeyExchange(sigType, sigHash, ka.version, clientHello.random, serverHello.random, serverECDHEParams)
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if err := verifyHandshakeSignature(sigType, cert.PublicKey, sigHash, signed, sig); err != nil {
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return errors.New("tls: invalid signature by the server certificate: " + err.Error())
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}
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return nil
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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.ckx == nil {
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return nil, nil, errors.New("tls: missing ServerKeyExchange message")
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}
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return ka.preMasterSecret, ka.ckx, nil
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}
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