// Executes the server side authentication and returns either the agreed secret
// session key or the a failure reason.
func (l *Listener) serverAuth(strm *stream.Stream, req *authRequest) ([]byte, error) {
// Create a new STS session
stsSess, err := sts.New(rand.Reader, config.StsGroup, config.StsGenerator,
config.StsCipher, config.StsCipherBits, config.StsSigHash)
if err != nil {
return nil, fmt.Errorf("failed to create STS session: %v", err)
}
// Accept the incoming key exchange request and send back own exp + auth token
exp, token, err := stsSess.Accept(rand.Reader, l.key, req.Exp)
if err != nil {
return nil, fmt.Errorf("failed to accept incoming exchange: %v", err)
}
if err = strm.Send(authChallenge{exp, token}); err != nil {
return nil, fmt.Errorf("failed to encode auth challenge: %v", err)
}
if err = strm.Flush(); err != nil {
return nil, fmt.Errorf("failed to flush auth challenge: %v", err)
}
// Receive the foreign auth token and if verifies conclude session
resp := new(authResponse)
if err = strm.Recv(resp); err != nil {
return nil, fmt.Errorf("failed to decode auth response: %v", err)
}
if err = stsSess.Finalize(&l.key.PublicKey, resp.Token); err != nil {
return nil, fmt.Errorf("failed to finalize exchange: %v", err)
}
return stsSess.Secret()
}
// Client side of the STS session negotiation.
func clientAuth(strm *stream.Stream, key *rsa.PrivateKey) ([]byte, error) {
// Set an overall time limit for the handshake to complete
strm.Sock().SetDeadline(time.Now().Add(config.SessionShakeTimeout))
defer strm.Sock().SetDeadline(time.Time{})
// Create a new empty session
stsSess, err := sts.New(rand.Reader, config.StsGroup, config.StsGenerator, config.StsCipher, config.StsCipherBits, config.StsSigHash)
if err != nil {
return nil, fmt.Errorf("failed to create new session: %v", err)
}
// Initiate a key exchange, send the exponential
exp, err := stsSess.Initiate()
if err != nil {
return nil, fmt.Errorf("failed to initiate key exchange: %v", err)
}
req := &initRequest{
Auth: &authRequest{exp},
}
if err = strm.Send(req); err != nil {
return nil, fmt.Errorf("failed to send auth request: %v", err)
}
if err = strm.Flush(); err != nil {
return nil, fmt.Errorf("failed to flush auth request: %v", err)
}
// Receive the foreign exponential and auth token and if verifies, send own auth
chall := new(authChallenge)
if err = strm.Recv(chall); err != nil {
return nil, fmt.Errorf("failed to receive auth challenge: %v", err)
}
token, err := stsSess.Verify(rand.Reader, key, &key.PublicKey, chall.Exp, chall.Token)
if err != nil {
return nil, fmt.Errorf("failed to verify acceptor auth token: %v", err)
}
if err = strm.Send(authResponse{token}); err != nil {
return nil, fmt.Errorf("failed to send auth response: %v", err)
}
if err = strm.Flush(); err != nil {
return nil, fmt.Errorf("failed to flush auth response: %v", err)
}
return stsSess.Secret()
}
// STS initiator: creates a new session, initiates a key exchange, verifies the other side and authenticates itself.
func initiator(group, generator *big.Int, cipher func([]byte) (cipher.Block, error), bits int,
hash crypto.Hash, skey *rsa.PrivateKey, pkey *rsa.PublicKey, trans, out chan []byte) {
// Create a new empty session
session, err := sts.New(rand.Reader, group, generator, cipher, bits, hash)
if err != nil {
fmt.Printf("failed to create new session: %v\n", err)
close(out)
return
}
// Initiate a key exchange, send the exponential
exp, err := session.Initiate()
if err != nil {
fmt.Printf("failed to initiate key exchange: %v\n", err)
close(out)
return
}
trans <- exp.Bytes()
// Receive the foreign exponential and auth token and if verifies, send own auth
bytes, token := <-trans, <-trans
exp = new(big.Int).SetBytes(bytes)
token, err = session.Verify(rand.Reader, skey, pkey, exp, token)
if err != nil {
fmt.Printf("failed to verify acceptor auth token: %v\n", err)
close(out)
return
}
trans <- token
// Protocol done, other side should finalize if all is correct
secret, err := session.Secret()
if err != nil {
fmt.Printf("failed to retrieve exchanged secret: %v\n", err)
close(out)
return
}
out <- secret
return
}
// STS acceptor: creates a new session, accepts an exchange request, authenticates itself and verifies the other side.
func acceptor(group, generator *big.Int, cipher func([]byte) (cipher.Block, error), bits int,
hash crypto.Hash, skey *rsa.PrivateKey, pkey *rsa.PublicKey, trans, out chan []byte) {
// Create a new empty session
session, err := sts.New(rand.Reader, group, generator, cipher, bits, hash)
if err != nil {
fmt.Printf("failed to create new session: %v\n", err)
close(out)
return
}
// Receive foreign exponential, accept the incoming key exchange request and send back own exp + auth token
bytes := <-trans
exp := new(big.Int).SetBytes(bytes)
exp, token, err := session.Accept(rand.Reader, skey, exp)
if err != nil {
fmt.Printf("failed to accept incoming exchange: %v\n", err)
close(out)
return
}
trans <- exp.Bytes()
trans <- token
// Receive the foreign auth token and if verifies conclude session
token = <-trans
err = session.Finalize(pkey, token)
if err != nil {
fmt.Printf("failed to finalize exchange: %v\n", err)
close(out)
return
}
// Protocol done
secret, err := session.Secret()
if err != nil {
fmt.Printf("failed to retrieve exchanged secret: %v\n", err)
close(out)
return
}
out <- secret
return
}