/gdata/tlslite/TLSConnection.py

"""
MAIN CLASS FOR TLS LITE (START HERE!).
"""
from __future__ import generators

import socket
from utils.compat import formatExceptionTrace
from TLSRecordLayer import TLSRecordLayer
from Session import Session
from constants import *
from utils.cryptomath import getRandomBytes
from errors import *
from messages import *
from mathtls import *
from HandshakeSettings import HandshakeSettings


class TLSConnection(TLSRecordLayer):
    """
    This class wraps a socket and provides TLS handshaking and data
    transfer.

    To use this class, create a new instance, passing a connected
    socket into the constructor.  Then call some handshake function.
    If the handshake completes without raising an exception, then a TLS
    connection has been negotiated.  You can transfer data over this
    connection as if it were a socket.

    This class provides both synchronous and asynchronous versions of
    its key functions.  The synchronous versions should be used when
    writing single-or multi-threaded code using blocking sockets.  The
    asynchronous versions should be used when performing asynchronous,
    event-based I/O with non-blocking sockets.

    Asynchronous I/O is a complicated subject; typically, you should
    not use the asynchronous functions directly, but should use some
    framework like asyncore or Twisted which TLS Lite integrates with
    (see
    L{tlslite.integration.TLSAsyncDispatcherMixIn.TLSAsyncDispatcherMixIn} or
    L{tlslite.integration.TLSTwistedProtocolWrapper.TLSTwistedProtocolWrapper}).
    """


    def __init__(self, sock):
        """Create a new TLSConnection instance.

        @param sock: The socket data will be transmitted on.  The
        socket should already be connected.  It may be in blocking or
        non-blocking mode.

        @type sock: L{socket.socket}
        """
        TLSRecordLayer.__init__(self, sock)

    def handshakeClientSRP(self, username, password, session=None,
                           settings=None, checker=None, async=False):
        """Perform an SRP handshake in the role of client.

        This function performs a TLS/SRP handshake.  SRP mutually
        authenticates both parties to each other using only a
        username and password.  This function may also perform a
        combined SRP and server-certificate handshake, if the server
        chooses to authenticate itself with a certificate chain in
        addition to doing SRP.

        TLS/SRP is non-standard.  Most TLS implementations don't
        support it.  See
        U{http://www.ietf.org/html.charters/tls-charter.html} or
        U{http://trevp.net/tlssrp/} for the latest information on
        TLS/SRP.

        Like any handshake function, this can be called on a closed
        TLS connection, or on a TLS connection that is already open.
        If called on an open connection it performs a re-handshake.

        If the function completes without raising an exception, the
        TLS connection will be open and available for data transfer.

        If an exception is raised, the connection will have been
        automatically closed (if it was ever open).

        @type username: str
        @param username: The SRP username.

        @type password: str
        @param password: The SRP password.

        @type session: L{tlslite.Session.Session}
        @param session: A TLS session to attempt to resume.  This
        session must be an SRP session performed with the same username
        and password as were passed in.  If the resumption does not
        succeed, a full SRP handshake will be performed.

        @type settings: L{tlslite.HandshakeSettings.HandshakeSettings}
        @param settings: Various settings which can be used to control
        the ciphersuites, certificate types, and SSL/TLS versions
        offered by the client.

        @type checker: L{tlslite.Checker.Checker}
        @param checker: A Checker instance.  This instance will be
        invoked to examine the other party's authentication
        credentials, if the handshake completes succesfully.

        @type async: bool
        @param async: If False, this function will block until the
        handshake is completed.  If True, this function will return a
        generator.  Successive invocations of the generator will
        return 0 if it is waiting to read from the socket, 1 if it is
        waiting to write to the socket, or will raise StopIteration if
        the handshake operation is completed.

        @rtype: None or an iterable
        @return: If 'async' is True, a generator object will be
        returned.

        @raise socket.error: If a socket error occurs.
        @raise tlslite.errors.TLSAbruptCloseError: If the socket is closed
        without a preceding alert.
        @raise tlslite.errors.TLSAlert: If a TLS alert is signalled.
        @raise tlslite.errors.TLSAuthenticationError: If the checker
        doesn't like the other party's authentication credentials.
        """
        handshaker = self._handshakeClientAsync(srpParams=(username, password),
                        session=session, settings=settings, checker=checker)
        if async:
            return handshaker
        for result in handshaker:
            pass

    def handshakeClientCert(self, certChain=None, privateKey=None,
                            session=None, settings=None, checker=None,
                            async=False):
        """Perform a certificate-based handshake in the role of client.

        This function performs an SSL or TLS handshake.  The server
        will authenticate itself using an X.509 or cryptoID certificate
        chain.  If the handshake succeeds, the server's certificate
        chain will be stored in the session's serverCertChain attribute.
        Unless a checker object is passed in, this function does no
        validation or checking of the server's certificate chain.

        If the server requests client authentication, the
        client will send the passed-in certificate chain, and use the
        passed-in private key to authenticate itself.  If no
        certificate chain and private key were passed in, the client
        will attempt to proceed without client authentication.  The
        server may or may not allow this.

        Like any handshake function, this can be called on a closed
        TLS connection, or on a TLS connection that is already open.
        If called on an open connection it performs a re-handshake.

        If the function completes without raising an exception, the
        TLS connection will be open and available for data transfer.

        If an exception is raised, the connection will have been
        automatically closed (if it was ever open).

        @type certChain: L{tlslite.X509CertChain.X509CertChain} or
        L{cryptoIDlib.CertChain.CertChain}
        @param certChain: The certificate chain to be used if the
        server requests client authentication.

        @type privateKey: L{tlslite.utils.RSAKey.RSAKey}
        @param privateKey: The private key to be used if the server
        requests client authentication.

        @type session: L{tlslite.Session.Session}
        @param session: A TLS session to attempt to resume.  If the
        resumption does not succeed, a full handshake will be
        performed.

        @type settings: L{tlslite.HandshakeSettings.HandshakeSettings}
        @param settings: Various settings which can be used to control
        the ciphersuites, certificate types, and SSL/TLS versions
        offered by the client.

        @type checker: L{tlslite.Checker.Checker}
        @param checker: A Checker instance.  This instance will be
        invoked to examine the other party's authentication
        credentials, if the handshake completes succesfully.

        @type async: bool
        @param async: If False, this function will block until the
        handshake is completed.  If True, this function will return a
        generator.  Successive invocations of the generator will
        return 0 if it is waiting to read from the socket, 1 if it is
        waiting to write to the socket, or will raise StopIteration if
        the handshake operation is completed.

        @rtype: None or an iterable
        @return: If 'async' is True, a generator object will be
        returned.

        @raise socket.error: If a socket error occurs.
        @raise tlslite.errors.TLSAbruptCloseError: If the socket is closed
        without a preceding alert.
        @raise tlslite.errors.TLSAlert: If a TLS alert is signalled.
        @raise tlslite.errors.TLSAuthenticationError: If the checker
        doesn't like the other party's authentication credentials.
        """
        handshaker = self._handshakeClientAsync(certParams=(certChain,
                        privateKey), session=session, settings=settings,
                        checker=checker)
        if async:
            return handshaker
        for result in handshaker:
            pass

    def handshakeClientUnknown(self, srpCallback=None, certCallback=None,
                               session=None, settings=None, checker=None,
                               async=False):
        """Perform a to-be-determined type of handshake in the role of client.

        This function performs an SSL or TLS handshake.  If the server
        requests client certificate authentication, the
        certCallback will be invoked and should return a (certChain,
        privateKey) pair.  If the callback returns None, the library
        will attempt to proceed without client authentication.  The
        server may or may not allow this.

        If the server requests SRP authentication, the srpCallback
        will be invoked and should return a (username, password) pair.
        If the callback returns None, the local implementation will
        signal a user_canceled error alert.

        After the handshake completes, the client can inspect the
        connection's session attribute to determine what type of
        authentication was performed.

        Like any handshake function, this can be called on a closed
        TLS connection, or on a TLS connection that is already open.
        If called on an open connection it performs a re-handshake.

        If the function completes without raising an exception, the
        TLS connection will be open and available for data transfer.

        If an exception is raised, the connection will have been
        automatically closed (if it was ever open).

        @type srpCallback: callable
        @param srpCallback: The callback to be used if the server
        requests SRP authentication.  If None, the client will not
        offer support for SRP ciphersuites.

        @type certCallback: callable
        @param certCallback: The callback to be used if the server
        requests client certificate authentication.

        @type session: L{tlslite.Session.Session}
        @param session: A TLS session to attempt to resume.  If the
        resumption does not succeed, a full handshake will be
        performed.

        @type settings: L{tlslite.HandshakeSettings.HandshakeSettings}
        @param settings: Various settings which can be used to control
        the ciphersuites, certificate types, and SSL/TLS versions
        offered by the client.

        @type checker: L{tlslite.Checker.Checker}
        @param checker: A Checker instance.  This instance will be
        invoked to examine the other party's authentication
        credentials, if the handshake completes succesfully.

        @type async: bool
        @param async: If False, this function will block until the
        handshake is completed.  If True, this function will return a
        generator.  Successive invocations of the generator will
        return 0 if it is waiting to read from the socket, 1 if it is
        waiting to write to the socket, or will raise StopIteration if
        the handshake operation is completed.

        @rtype: None or an iterable
        @return: If 'async' is True, a generator object will be
        returned.

        @raise socket.error: If a socket error occurs.
        @raise tlslite.errors.TLSAbruptCloseError: If the socket is closed
        without a preceding alert.
        @raise tlslite.errors.TLSAlert: If a TLS alert is signalled.
        @raise tlslite.errors.TLSAuthenticationError: If the checker
        doesn't like the other party's authentication credentials.
        """
        handshaker = self._handshakeClientAsync(unknownParams=(srpCallback,
                        certCallback), session=session, settings=settings,
                        checker=checker)
        if async:
            return handshaker
        for result in handshaker:
            pass

    def handshakeClientSharedKey(self, username, sharedKey, settings=None,
                                 checker=None, async=False):
        """Perform a shared-key handshake in the role of client.

        This function performs a shared-key handshake.  Using shared
        symmetric keys of high entropy (128 bits or greater) mutually
        authenticates both parties to each other.

        TLS with shared-keys is non-standard.  Most TLS
        implementations don't support it.  See
        U{http://www.ietf.org/html.charters/tls-charter.html} for the
        latest information on TLS with shared-keys.  If the shared-keys
        Internet-Draft changes or is superceded, TLS Lite will track
        those changes, so the shared-key support in later versions of
        TLS Lite may become incompatible with this version.

        Like any handshake function, this can be called on a closed
        TLS connection, or on a TLS connection that is already open.
        If called on an open connection it performs a re-handshake.

        If the function completes without raising an exception, the
        TLS connection will be open and available for data transfer.

        If an exception is raised, the connection will have been
        automatically closed (if it was ever open).

        @type username: str
        @param username: The shared-key username.

        @type sharedKey: str
        @param sharedKey: The shared key.

        @type settings: L{tlslite.HandshakeSettings.HandshakeSettings}
        @param settings: Various settings which can be used to control
        the ciphersuites, certificate types, and SSL/TLS versions
        offered by the client.

        @type checker: L{tlslite.Checker.Checker}
        @param checker: A Checker instance.  This instance will be
        invoked to examine the other party's authentication
        credentials, if the handshake completes succesfully.

        @type async: bool
        @param async: If False, this function will block until the
        handshake is completed.  If True, this function will return a
        generator.  Successive invocations of the generator will
        return 0 if it is waiting to read from the socket, 1 if it is
        waiting to write to the socket, or will raise StopIteration if
        the handshake operation is completed.

        @rtype: None or an iterable
        @return: If 'async' is True, a generator object will be
        returned.

        @raise socket.error: If a socket error occurs.
        @raise tlslite.errors.TLSAbruptCloseError: If the socket is closed
        without a preceding alert.
        @raise tlslite.errors.TLSAlert: If a TLS alert is signalled.
        @raise tlslite.errors.TLSAuthenticationError: If the checker
        doesn't like the other party's authentication credentials.
        """
        handshaker = self._handshakeClientAsync(sharedKeyParams=(username,
                        sharedKey), settings=settings, checker=checker)
        if async:
            return handshaker
        for result in handshaker:
            pass

    def _handshakeClientAsync(self, srpParams=(), certParams=(),
                             unknownParams=(), sharedKeyParams=(),
                             session=None, settings=None, checker=None,
                             recursive=False):

        handshaker = self._handshakeClientAsyncHelper(srpParams=srpParams,
                certParams=certParams, unknownParams=unknownParams,
                sharedKeyParams=sharedKeyParams, session=session,
                settings=settings, recursive=recursive)
        for result in self._handshakeWrapperAsync(handshaker, checker):
            yield result


    def _handshakeClientAsyncHelper(self, srpParams, certParams, unknownParams,
                               sharedKeyParams, session, settings, recursive):
        if not recursive:
            self._handshakeStart(client=True)

        #Unpack parameters
        srpUsername = None      # srpParams
        password = None         # srpParams
        clientCertChain = None  # certParams
        privateKey = None       # certParams
        srpCallback = None      # unknownParams
        certCallback = None     # unknownParams
        #session                # sharedKeyParams (or session)
        #settings               # settings

        if srpParams:
            srpUsername, password = srpParams
        elif certParams:
            clientCertChain, privateKey = certParams
        elif unknownParams:
            srpCallback, certCallback = unknownParams
        elif sharedKeyParams:
            session = Session()._createSharedKey(*sharedKeyParams)

        if not settings:
            settings = HandshakeSettings()
        settings = settings._filter()

        #Validate parameters
        if srpUsername and not password:
            raise ValueError("Caller passed a username but no password")
        if password and not srpUsername:
            raise ValueError("Caller passed a password but no username")

        if clientCertChain and not privateKey:
            raise ValueError("Caller passed a certChain but no privateKey")
        if privateKey and not clientCertChain:
            raise ValueError("Caller passed a privateKey but no certChain")

        if clientCertChain:
            foundType = False
            try:
                import cryptoIDlib.CertChain
                if isinstance(clientCertChain, cryptoIDlib.CertChain.CertChain):
                    if "cryptoID" not in settings.certificateTypes:
                        raise ValueError("Client certificate doesn't "\
                                         "match Handshake Settings")
                    settings.certificateTypes = ["cryptoID"]
                    foundType = True
            except ImportError:
                pass
            if not foundType and isinstance(clientCertChain,
                                            X509CertChain):
                if "x509" not in settings.certificateTypes:
                    raise ValueError("Client certificate doesn't match "\
                                     "Handshake Settings")
                settings.certificateTypes = ["x509"]
                foundType = True
            if not foundType:
                raise ValueError("Unrecognized certificate type")


        if session:
            if not session.valid():
                session = None #ignore non-resumable sessions...
            elif session.resumable and \
                    (session.srpUsername != srpUsername):
                raise ValueError("Session username doesn't match")

        #Add Faults to parameters
        if srpUsername and self.fault == Fault.badUsername:
            srpUsername += "GARBAGE"
        if password and self.fault == Fault.badPassword:
            password += "GARBAGE"
        if sharedKeyParams:
            identifier = sharedKeyParams[0]
            sharedKey = sharedKeyParams[1]
            if self.fault == Fault.badIdentifier:
                identifier += "GARBAGE"
                session = Session()._createSharedKey(identifier, sharedKey)
            elif self.fault == Fault.badSharedKey:
                sharedKey += "GARBAGE"
                session = Session()._createSharedKey(identifier, sharedKey)


        #Initialize locals
        serverCertChain = None
        cipherSuite = 0
        certificateType = CertificateType.x509
        premasterSecret = None

        #Get client nonce
        clientRandom = getRandomBytes(32)

        #Initialize acceptable ciphersuites
        cipherSuites = []
        if srpParams:
            cipherSuites += CipherSuite.getSrpRsaSuites(settings.cipherNames)
            cipherSuites += CipherSuite.getSrpSuites(settings.cipherNames)
        elif certParams:
            cipherSuites += CipherSuite.getRsaSuites(settings.cipherNames)
        elif unknownParams:
            if srpCallback:
                cipherSuites += \
                    CipherSuite.getSrpRsaSuites(settings.cipherNames)
                cipherSuites += \
                    CipherSuite.getSrpSuites(settings.cipherNames)
            cipherSuites += CipherSuite.getRsaSuites(settings.cipherNames)
        elif sharedKeyParams:
            cipherSuites += CipherSuite.getRsaSuites(settings.cipherNames)
        else:
            cipherSuites += CipherSuite.getRsaSuites(settings.cipherNames)

        #Initialize acceptable certificate types
        certificateTypes = settings._getCertificateTypes()

        #Tentatively set the version to the client's minimum version.
        #We'll use this for the ClientHello, and if an error occurs
        #parsing the Server Hello, we'll use this version for the response
        self.version = settings.maxVersion

        #Either send ClientHello (with a resumable session)...
        if session:
            #If it's a resumable (i.e. not a shared-key session), then its
            #ciphersuite must be one of the acceptable ciphersuites
            if (not sharedKeyParams) and \
                session.cipherSuite not in cipherSuites:
                raise ValueError("Session's cipher suite not consistent "\
                                 "with parameters")
            else:
                clientHello = ClientHello()
                clientHello.create(settings.maxVersion, clientRandom,
                                   session.sessionID, cipherSuites,
                                   certificateTypes, session.srpUsername)

        #Or send ClientHello (without)
        else:
            clientHello = ClientHello()
            clientHello.create(settings.maxVersion, clientRandom,
                               createByteArraySequence([]), cipherSuites,
                               certificateTypes, srpUsername)
        for result in self._sendMsg(clientHello):
            yield result

        #Get ServerHello (or missing_srp_username)
        for result in self._getMsg((ContentType.handshake,
                                  ContentType.alert),
                                  HandshakeType.server_hello):
            if result in (0,1):
                yield result
            else:
                break
        msg = result

        if isinstance(msg, ServerHello):
            serverHello = msg
        elif isinstance(msg, Alert):
            alert = msg

            #If it's not a missing_srp_username, re-raise
            if alert.description != AlertDescription.missing_srp_username:
                self._shutdown(False)
                raise TLSRemoteAlert(alert)

            #If we're not in SRP callback mode, we won't have offered SRP
            #without a username, so we shouldn't get this alert
            if not srpCallback:
                for result in self._sendError(\
                                AlertDescription.unexpected_message):
                    yield result
            srpParams = srpCallback()
            #If the callback returns None, cancel the handshake
            if srpParams == None:
                for result in self._sendError(AlertDescription.user_canceled):
                    yield result

            #Recursively perform handshake
            for result in self._handshakeClientAsyncHelper(srpParams,
                            None, None, None, None, settings, True):
                yield result
            return

        #Get the server version.  Do this before anything else, so any
        #error alerts will use the server's version
        self.version = serverHello.server_version

        #Future responses from server must use this version
        self._versionCheck = True

        #Check ServerHello
        if serverHello.server_version < settings.minVersion:
            for result in self._sendError(\
                AlertDescription.protocol_version,
                "Too old version: %s" % str(serverHello.server_version)):
                yield result
        if serverHello.server_version > settings.maxVersion:
            for result in self._sendError(\
                AlertDescription.protocol_version,
                "Too new version: %s" % str(serverHello.server_version)):
                yield result
        if serverHello.cipher_suite not in cipherSuites:
            for result in self._sendError(\
                AlertDescription.illegal_parameter,
                "Server responded with incorrect ciphersuite"):
                yield result
        if serverHello.certificate_type not in certificateTypes:
            for result in self._sendError(\
                AlertDescription.illegal_parameter,
                "Server responded with incorrect certificate type"):
                yield result
        if serverHello.compression_method != 0:
            for result in self._sendError(\
                AlertDescription.illegal_parameter,
                "Server responded with incorrect compression method"):
                yield result

        #Get the server nonce
        serverRandom = serverHello.random

        #If the server agrees to resume
        if session and session.sessionID and \
                       serverHello.session_id == session.sessionID:

            #If a shared-key, we're flexible about suites; otherwise the
            #server-chosen suite has to match the session's suite
            if sharedKeyParams:
                session.cipherSuite = serverHello.cipher_suite
            elif serverHello.cipher_suite != session.cipherSuite:
                for result in self._sendError(\
                    AlertDescription.illegal_parameter,\
                    "Server's ciphersuite doesn't match session"):
                    yield result

            #Set the session for this connection
            self.session = session

            #Calculate pending connection states
            self._calcPendingStates(clientRandom, serverRandom,
                                   settings.cipherImplementations)

            #Exchange ChangeCipherSpec and Finished messages
            for result in self._getFinished():
                yield result
            for result in self._sendFinished():
                yield result

            #Mark the connection as open
            self._handshakeDone(resumed=True)

        #If server DOES NOT agree to resume
        else:

            if sharedKeyParams:
                for result in self._sendError(\
                        AlertDescription.user_canceled,
                        "Was expecting a shared-key resumption"):
                    yield result

            #We've already validated these
            cipherSuite = serverHello.cipher_suite
            certificateType = serverHello.certificate_type

            #If the server chose an SRP suite...
            if cipherSuite in CipherSuite.srpSuites:
                #Get ServerKeyExchange, ServerHelloDone
                for result in self._getMsg(ContentType.handshake,
                        HandshakeType.server_key_exchange, cipherSuite):
                    if result in (0,1):
                        yield result
                    else:
                        break
                serverKeyExchange = result

                for result in self._getMsg(ContentType.handshake,
                        HandshakeType.server_hello_done):
                    if result in (0,1):
                        yield result
                    else:
                        break
                serverHelloDone = result

            #If the server chose an SRP+RSA suite...
            elif cipherSuite in CipherSuite.srpRsaSuites:
                #Get Certificate, ServerKeyExchange, ServerHelloDone
                for result in self._getMsg(ContentType.handshake,
                        HandshakeType.certificate, certificateType):
                    if result in (0,1):
                        yield result
                    else:
                        break
                serverCertificate = result

                for result in self._getMsg(ContentType.handshake,
                        HandshakeType.server_key_exchange, cipherSuite):
                    if result in (0,1):
                        yield result
                    else:
                        break
                serverKeyExchange = result

                for result in self._getMsg(ContentType.handshake,
                        HandshakeType.server_hello_done):
                    if result in (0,1):
                        yield result
                    else:
                        break
                serverHelloDone = result

            #If the server chose an RSA suite...
            elif cipherSuite in CipherSuite.rsaSuites:
                #Get Certificate[, CertificateRequest], ServerHelloDone
                for result in self._getMsg(ContentType.handshake,
                        HandshakeType.certificate, certificateType):
                    if result in (0,1):
                        yield result
                    else:
                        break
                serverCertificate = result

                for result in self._getMsg(ContentType.handshake,
                        (HandshakeType.server_hello_done,
                        HandshakeType.certificate_request)):
                    if result in (0,1):
                        yield result
                    else:
                        break
                msg = result

                certificateRequest = None
                if isinstance(msg, CertificateRequest):
                    certificateRequest = msg
                    for result in self._getMsg(ContentType.handshake,
                            HandshakeType.server_hello_done):
                        if result in (0,1):
                            yield result
                        else:
                            break
                    serverHelloDone = result
                elif isinstance(msg, ServerHelloDone):
                    serverHelloDone = msg
            else:
                raise AssertionError()


            #Calculate SRP premaster secret, if server chose an SRP or
            #SRP+RSA suite
            if cipherSuite in CipherSuite.srpSuites + \
                              CipherSuite.srpRsaSuites:
                #Get and check the server's group parameters and B value
                N = serverKeyExchange.srp_N
                g = serverKeyExchange.srp_g
                s = serverKeyExchange.srp_s
                B = serverKeyExchange.srp_B

                if (g,N) not in goodGroupParameters:
                    for result in self._sendError(\
                            AlertDescription.untrusted_srp_parameters,
                            "Unknown group parameters"):
                        yield result
                if numBits(N) < settings.minKeySize:
                    for result in self._sendError(\
                            AlertDescription.untrusted_srp_parameters,
                            "N value is too small: %d" % numBits(N)):
                        yield result
                if numBits(N) > settings.maxKeySize:
                    for result in self._sendError(\
                            AlertDescription.untrusted_srp_parameters,
                            "N value is too large: %d" % numBits(N)):
                        yield result
                if B % N == 0:
                    for result in self._sendError(\
                            AlertDescription.illegal_parameter,
                            "Suspicious B value"):
                        yield result

                #Check the server's signature, if server chose an
                #SRP+RSA suite
                if cipherSuite in CipherSuite.srpRsaSuites:
                    #Hash ServerKeyExchange/ServerSRPParams
                    hashBytes = serverKeyExchange.hash(clientRandom,
                                                       serverRandom)

                    #Extract signature bytes from ServerKeyExchange
                    sigBytes = serverKeyExchange.signature
                    if len(sigBytes) == 0:
                        for result in self._sendError(\
                                AlertDescription.illegal_parameter,
                                "Server sent an SRP ServerKeyExchange "\
                                "message without a signature"):
                            yield result

                    #Get server's public key from the Certificate message
                    for result in self._getKeyFromChain(serverCertificate,
                                                       settings):
                        if result in (0,1):
                            yield result
                        else:
                            break
                    publicKey, serverCertChain = result

                    #Verify signature
                    if not publicKey.verify(sigBytes, hashBytes):
                        for result in self._sendError(\
                                AlertDescription.decrypt_error,
                                "Signature failed to verify"):
                            yield result


                #Calculate client's ephemeral DH values (a, A)
                a = bytesToNumber(getRandomBytes(32))
                A = powMod(g, a, N)

                #Calculate client's static DH values (x, v)
                x = makeX(bytesToString(s), srpUsername, password)
                v = powMod(g, x, N)

                #Calculate u
                u = makeU(N, A, B)

                #Calculate premaster secret
                k = makeK(N, g)
                S = powMod((B - (k*v)) % N, a+(u*x), N)

                if self.fault == Fault.badA:
                    A = N
                    S = 0
                premasterSecret = numberToBytes(S)

                #Send ClientKeyExchange
                for result in self._sendMsg(\
                        ClientKeyExchange(cipherSuite).createSRP(A)):
                    yield result


            #Calculate RSA premaster secret, if server chose an RSA suite
            elif cipherSuite in CipherSuite.rsaSuites:

                #Handle the presence of a CertificateRequest
                if certificateRequest:
                    if unknownParams and certCallback:
                        certParamsNew = certCallback()
                        if certParamsNew:
                            clientCertChain, privateKey = certParamsNew

                #Get server's public key from the Certificate message
                for result in self._getKeyFromChain(serverCertificate,
                                                   settings):
                    if result in (0,1):
                        yield result
                    else:
                        break
                publicKey, serverCertChain = result


                #Calculate premaster secret
                premasterSecret = getRandomBytes(48)
                premasterSecret[0] = settings.maxVersion[0]
                premasterSecret[1] = settings.maxVersion[1]

                if self.fault == Fault.badPremasterPadding:
                    premasterSecret[0] = 5
                if self.fault == Fault.shortPremasterSecret:
                    premasterSecret = premasterSecret[:-1]

                #Encrypt premaster secret to server's public key
                encryptedPreMasterSecret = publicKey.encrypt(premasterSecret)

                #If client authentication was requested, send Certificate
                #message, either with certificates or empty
                if certificateRequest:
                    clientCertificate = Certificate(certificateType)

                    if clientCertChain:
                        #Check to make sure we have the same type of
                        #certificates the server requested
                        wrongType = False
                        if certificateType == CertificateType.x509:
                            if not isinstance(clientCertChain, X509CertChain):
                                wrongType = True
                        elif certificateType == CertificateType.cryptoID:
                            if not isinstance(clientCertChain,
                                              cryptoIDlib.CertChain.CertChain):
                                wrongType = True
                        if wrongType:
                            for result in self._sendError(\
                                    AlertDescription.handshake_failure,
                                    "Client certificate is of wrong type"):
                                yield result

                        clientCertificate.create(clientCertChain)

                    for result in self._sendMsg(clientCertificate):
                        yield result
                else:
                    #The server didn't request client auth, so we
                    #zeroize these so the clientCertChain won't be
                    #stored in the session.
                    privateKey = None
                    clientCertChain = None

                #Send ClientKeyExchange
                clientKeyExchange = ClientKeyExchange(cipherSuite,
                                                      self.version)
                clientKeyExchange.createRSA(encryptedPreMasterSecret)
                for result in self._sendMsg(clientKeyExchange):
                    yield result

                #If client authentication was requested and we have a
                #private key, send CertificateVerify
                if certificateRequest and privateKey:
                    if self.version == (3,0):
                        #Create a temporary session object, just for the
                        #purpose of creating the CertificateVerify
                        session = Session()
                        session._calcMasterSecret(self.version,
                                                 premasterSecret,
                                                 clientRandom,
                                                 serverRandom)
                        verifyBytes = self._calcSSLHandshakeHash(\
                                          session.masterSecret, "")
                    elif self.version in ((3,1), (3,2)):
                        verifyBytes = stringToBytes(\
                            self._handshake_md5.digest() + \
                            self._handshake_sha.digest())
                    if self.fault == Fault.badVerifyMessage:
                        verifyBytes[0] = ((verifyBytes[0]+1) % 256)
                    signedBytes = privateKey.sign(verifyBytes)
                    certificateVerify = CertificateVerify()
                    certificateVerify.create(signedBytes)
                    for result in self._sendMsg(certificateVerify):
                        yield result


            #Create the session object
            self.session = Session()
            self.session._calcMasterSecret(self.version, premasterSecret,
                                          clientRandom, serverRandom)
            self.session.sessionID = serverHello.session_id
            self.session.cipherSuite = cipherSuite
            self.session.srpUsername = srpUsername
            self.session.clientCertChain = clientCertChain
            self.session.serverCertChain = serverCertChain

            #Calculate pending connection states
            self._calcPendingStates(clientRandom, serverRandom,
                                   settings.cipherImplementations)

            #Exchange ChangeCipherSpec and Finished messages
            for result in self._sendFinished():
                yield result
            for result in self._getFinished():
                yield result

            #Mark the connection as open
            self.session._setResumable(True)
            self._handshakeDone(resumed=False)



    def handshakeServer(self, sharedKeyDB=None, verifierDB=None,
                        certChain=None, privateKey=None, reqCert=False,
                        sessionCache=None, settings=None, checker=None):
        """Perform a handshake in the role of server.

        This function performs an SSL or TLS handshake.  Depending on
        the arguments and the behavior of the client, this function can
        perform a shared-key, SRP, or certificate-based handshake.  It
        can also perform a combined SRP and server-certificate
        handshake.

        Like any handshake function, this can be called on a closed
        TLS connection, or on a TLS connection that is already open.
        If called on an open connection it performs a re-handshake.
        This function does not send a Hello Request message before
        performing the handshake, so if re-handshaking is required,
        the server must signal the client to begin the re-handshake
        through some other means.

        If the function completes without raising an exception, the
        TLS connection will be open and available for data transfer.

        If an exception is raised, the connection will have been
        automatically closed (if it was ever open).

        @type sharedKeyDB: L{tlslite.SharedKeyDB.SharedKeyDB}
        @param sharedKeyDB: A database of shared symmetric keys
        associated with usernames.  If the client performs a
        shared-key handshake, the session's sharedKeyUsername
        attribute will be set.

        @type verifierDB: L{tlslite.VerifierDB.VerifierDB}
        @param verifierDB: A database of SRP password verifiers
        associated with usernames.  If the client performs an SRP
        handshake, the session's srpUsername attribute will be set.

        @type certChain: L{tlslite.X509CertChain.X509CertChain} or
        L{cryptoIDlib.CertChain.CertChain}
        @param certChain: The certificate chain to be used if the
        client requests server certificate authentication.

        @type privateKey: L{tlslite.utils.RSAKey.RSAKey}
        @param privateKey: The private key to be used if the client
        requests server certificate authentication.

        @type reqCert: bool
        @param reqCert: Whether to request client certificate
        authentication.  This only applies if the client chooses server
        certificate authentication; if the client chooses SRP or
        shared-key authentication, this will be ignored.  If the client
        performs a client certificate authentication, the sessions's
        clientCertChain attribute will be set.

        @type sessionCache: L{tlslite.SessionCache.SessionCache}
        @param sessionCache: An in-memory cache of resumable sessions.
        The client can resume sessions from this cache.  Alternatively,
        if the client performs a full handshake, a new session will be
        added to the cache.

        @type settings: L{tlslite.HandshakeSettings.HandshakeSettings}
        @param settings: Various settings which can be used to control
        the ciphersuites and SSL/TLS version chosen by the server.

        @type checker: L{tlslite.Checker.Checker}
        @param checker: A Checker instance.  This instance will be
        invoked to examine the other party's authentication
        credentials, if the handshake completes succesfully.

        @raise socket.error: If a socket error occurs.
        @raise tlslite.errors.TLSAbruptCloseError: If the socket is closed
        without a preceding alert.
        @raise tlslite.errors.TLSAlert: If a TLS alert is signalled.
        @raise tlslite.errors.TLSAuthenticationError: If the checker
        doesn't like the other party's authentication credentials.
        """
        for result in self.handshakeServerAsync(sharedKeyDB, verifierDB,
                certChain, privateKey, reqCert, sessionCache, settings,
                checker):
            pass


    def handshakeServerAsync(self, sharedKeyDB=None, verifierDB=None,
                             certChain=None, privateKey=None, reqCert=False,
                             sessionCache=None, settings=None, checker=None):
        """Start a server handshake operation on the TLS connection.

        This function returns a generator which behaves similarly to
        handshakeServer().  Successive invocations of the generator
        will return 0 if it is waiting to read from the socket, 1 if it is
        waiting to write to the socket, or it will raise StopIteration
        if the handshake operation is complete.

        @rtype: iterable
        @return: A generator; see above for details.
        """
        handshaker = self._handshakeServerAsyncHelper(\
            sharedKeyDB=sharedKeyDB,
            verifierDB=verifierDB, certChain=certChain,
            privateKey=privateKey, reqCert=reqCert,
            sessionCache=sessionCache, settings=settings)
        for result in self._handshakeWrapperAsync(handshaker, checker):
            yield result


    def _handshakeServerAsyncHelper(self, sharedKeyDB, verifierDB,
                             certChain, privateKey, reqCert, sessionCache,
                             settings):

        self._handshakeStart(client=False)

        if (not sharedKeyDB) and (not verifierDB) and (not certChain):
            raise ValueError("Caller passed no authentication credentials")
        if certChain and not privateKey:
            raise ValueError("Caller passed a certChain but no privateKey")
        if privateKey and not certChain:
            raise ValueError("Caller passed a privateKey but no certChain")

        if not settings:
            settings = HandshakeSettings()
        settings = settings._filter()

        #Initialize acceptable cipher suites
        cipherSuites = []
        if verifierDB:
            if certChain:
                cipherSuites += \
                    CipherSuite.getSrpRsaSuites(settings.cipherNames)
            cipherSuites += CipherSuite.getSrpSuites(settings.cipherNames)
        if sharedKeyDB or certChain:
            cipherSuites += CipherSuite.getRsaSuites(settings.cipherNames)

        #Initialize acceptable certificate type
        certificateType = None
        if certChain:
            try:
                import cryptoIDlib.CertChain
                if isinstance(certChain, cryptoIDlib.CertChain.CertChain):
                    certificateType = CertificateType.cryptoID
            except ImportError:
                pass
            if isinstance(certChain, X509CertChain):
                certificateType = CertificateType.x509
            if certificateType == None:
                raise ValueError("Unrecognized certificate type")

        #Initialize locals
        clientCertChain = None
        serverCertChain = None #We may set certChain to this later
        postFinishedError = None

        #Tentatively set version to most-desirable version, so if an error
        #occurs parsing the ClientHello, this is what we'll use for the
        #error alert
        self.version = settings.maxVersion

        #Get ClientHello
        for result in self._getMsg(ContentType.handshake,
                                   HandshakeType.client_hello):
            if result in (0,1):
                yield result
            else:
                break
        clientHello = result

        #If client's version is too low, reject it
        if clientHello.client_version < settings.minVersion:
            self.version = settings.minVersion
            for result in self._sendError(\
                  AlertDescription.protocol_version,
                  "Too old version: %s" % str(clientHello.client_version)):
                yield result

        #If client's version is too high, propose my highest version
        elif clientHello.client_version > settings.maxVersion:
            self.version = settings.maxVersion

        else:
            #Set the version to the client's version
            self.version = clientHello.client_version

        #Get the client nonce; create server nonce
        clientRandom = clientHello.random
        serverRandom = getRandomBytes(32)

        #Calculate the first cipher suite intersection.
        #This is the 'privileged' ciphersuite.  We'll use it if we're
        #doing a shared-key resumption or a new negotiation.  In fact,
        #the only time we won't use it is if we're resuming a non-sharedkey
        #session, in which case we use the ciphersuite from the session.
        #
        #Given the current ciphersuite ordering, this means we prefer SRP
        #over non-SRP.
        for cipherSuite in cipherSuites:
            if cipherSuite in clientHello.cipher_suites:
                break
        else:
            for result in self._sendError(\
                    AlertDescription.handshake_failure):
                yield result

        #If resumption was requested...
        if clientHello.session_id and (sharedKeyDB or sessionCache):
            session = None

            #Check in the sharedKeys container
            if sharedKeyDB and len(clientHello.session_id)==16:
                try:
                    #Trim off zero padding, if any
                    for x in range(16):
                        if clientHello.session_id[x]==0:
                            break
                    self.allegedSharedKeyUsername = bytesToString(\
                                            clientHello.session_id[:x])
                    session = sharedKeyDB[self.allegedSharedKeyUsername]
                    if not session.sharedKey:
                        raise AssertionError()
                    #use privileged ciphersuite
                    session.cipherSuite = cipherSuite
                except KeyError:
                    pass

            #Then check in the session cache
            if sessionCache and not session:
                try:
                    session = sessionCache[bytesToString(\
                                               clientHello.session_id)]
                    if session.sharedKey:
                        raise AssertionError()
                    if not session.resumable:
                        raise AssertionError()
                    #Check for consistency with ClientHello
                    if session.cipherSuite not in cipherSuites:
                        for result in self._sendError(\
                                AlertDescription.handshake_failure):
                            yield result
                    if session.cipherSuite not in clientHello.cipher_suites:
                        for result in self._sendError(\
                                AlertDescription.handshake_failure):
                            yield result
                    if clientHello.srp_username:
                        if clientHello.srp_username != session.srpUsername:
                            for result in self._sendError(\
                                    AlertDescription.handshake_failure):
                                yield result
                except KeyError:
                    pass

            #If a session is found..
            if session:
                #Set the session
                self.session = session

                #Send ServerHello
                serverHello = ServerHello()
                serverHello.create(self.version, serverRandom,
                                   session.sessionID, session.cipherSuite,
                                   certificateType)
                for result in self._sendMsg(serverHello):
                    yield result

                #From here on, the client's messages must have the right version
                self._versionCheck = True

                #Calculate pending connection states
                self._calcPendingStates(clientRandom, serverRandom,
                                       settings.cipherImplementations)

                #Exchange ChangeCipherSpec and Finished messages
                for result in self._sendFinished():
                    yield result
                for result in self._getFinished():
                    yield result

                #Mark the connection as open
                self._handshakeDone(resumed=True)
                return


        #If not a resumption...

        #TRICKY: we might have chosen an RSA suite that was only deemed
        #acceptable because of the shared-key resumption.  If the shared-
        #key resumption failed, because the identifier wasn't recognized,
        #we might fall through to here, where we have an RSA suite
        #chosen, but no certificate.
        if cipherSuite in CipherSuite.rsaSuites and not certChain:
            for result in self._sendError(\
                    AlertDescription.handshake_failure):
                yield result

        #If an RSA suite is chosen, check for certificate type intersection
        #(We do this check down here because if the mismatch occurs but the
        # client is using a shared-key session, it's okay)
        if cipherSuite in CipherSuite.rsaSuites + \
                          CipherSuite.srpRsaSuites:
            if certificateType not in clientHello.certificate_types:
                for result in self._sendError(\
                        AlertDescription.handshake_failure,
                        "the client doesn't support my certificate type"):
                    yield result

            #Move certChain -> serverCertChain, now that we're using it
            serverCertChain = certChain


        #Create sessionID
        if sessionCache:
            sessionID = getRandomBytes(32)
        else:
            sessionID = createByteArraySequence([])

        #If we've selected an SRP suite, exchange keys and calculate
        #premaster secret:
        if cipherSuite in CipherSuite.srpSuites + CipherSuite.srpRsaSuites:

            #If there's no SRP username...
            if not clientHello.srp_username:

                #Ask the client to re-send ClientHello with one
                for result in self._sendMsg(Alert().create(\
                        AlertDescription.missing_srp_username,
                        AlertLevel.warning)):
                    yield result

                #Get ClientHello
                for result in self._getMsg(ContentType.handshake,
                        HandshakeType.client_hello):
                    if result in (0,1):
                        yield result
                    else:
                        break
                clientHello = result

                #Check ClientHello
                #If client's version is too low, reject it (COPIED CODE; BAD!)
                if clientHello.client_version < settings.minVersion:
                    self.version = settings.minVersion
                    for result in self._sendError(\
                          AlertDescription.protocol_version,
                          "Too old version: %s" % str(clientHello.client_version)):
                        yield result

                #If client's version is too high, propose my highest version
                elif clientHello.client_version > settings.maxVersion:
                    self.version = settings.maxVersion

                else:
                    #Set the version to the client's version
                    self.version = clientHello.client_version

                #Recalculate the privileged cipher suite, making sure to
                #pick an SRP suite
                cipherSuites = [c for c in cipherSuites if c in \
                                CipherSuite.srpSuites + \
                                CipherSuite.srpRsaSuites]
                for cipherSuite in cipherSuites:
                    if cipherSuite in clientHello.cipher_suites:
                        break
                else:
                    for result in self._sendError(\
                            AlertDescription.handshake_failure):
                        yield result

                #Get the client nonce; create server nonce
                clientRandom = clientHello.random
                serverRandom = getRandomBytes(32)

                #The username better be there, this time
                if not clientHello.srp_username:
                    for result in self._sendError(\
                            AlertDescription.illegal_parameter,
                            "Client resent a hello, but without the SRP"\
                            " username"):
                        yield result


            #Get username
            self.allegedSrpUsername = clientHello.srp_username

            #Get parameters from username
            try:
                entry = verifierDB[self.allegedSrpUsername]
            except KeyError:
                for result in self._sendError(\
                        AlertDescription.unknown_srp_username):
                    yield result
            (N, g, s, v) = entry

            #Calculate server's ephemeral DH values (b, B)
            b = bytesToNumber(getRandomBytes(32))
            k = makeK(N, g)
            B = (powMod(g, b, N) + (k*v)) % N

            #Create ServerKeyExchange, signing it if necessary
            serverKeyExchange = ServerKeyExchange(cipherSuite)
            serverKeyExchange.createSRP(N, g, stringToBytes(s), B)
            if cipherSuite in CipherSuite.srpRsaSuites:
                hashBytes = serverKeyExchange.hash(clientRandom,
                                                   serverRandom)
                serverKeyExchange.signature = privateKey.sign(hashBytes)

            #Send ServerHello[, Certificate], ServerKeyExchange,
            #ServerHelloDone
            msgs = []
            serverHello = ServerHello()
            serverHello.create(self.version, serverRandom, sessionID,
                               cipherSuite, certificateType)
            msgs.append(serverHello)
            if cipherSuite in CipherSuite.srpRsaSuites:
                certificateMsg = Certificate(certificateType)
                certificateMsg.create(serverCertChain)
                msgs.append(certificateMsg)
            msgs.append(serverKeyExchange)
            msgs.append(ServerHelloDone())
            for result in self._sendMsgs(msgs):
                yield result

            #From here on, the client's messages must have the right version
            self._versionCheck = True

            #Get and check ClientKeyExchange
            for result in self._getMsg(ContentType.handshake,
                                      HandshakeType.client_key_exchange,
                                      cipherSuite):
                if result in (0,1):
                    yield result
                else:
                    break
            clientKeyExchange = result
            A = clientKeyExchange.srp_A
            if A % N == 0:
                postFinishedError = (AlertDescription.illegal_parameter,
                                     "Suspicious A value")
            #Calculate u
            u = makeU(N, A, B)

            #Calculate premaster secret
            S = powMod((A * powMod(v,u,N)) % N, b, N)
            premasterSecret = numberToBytes(S)


        #If we've selected an RSA suite, exchange keys and calculate
        #premaster secret:
        elif cipherSuite in CipherSuite.rsaSuites:

            #Send ServerHello, Certificate[, CertificateRequest],
            #ServerHelloDone
            msgs = []
            msgs.append(ServerHello().create(self.version, serverRandom,
                        sessionID, cipherSuite, certificateType))
            msgs.append(Certificate(certificateType).create(serverCertChain))
            if reqCert:
                msgs.append(CertificateRequest())
            msgs.append(ServerHelloDone())
            for result in self._sendMsgs(msgs):
                yield result

            #From here on, the client's messages must have the right version
            self._versionCheck = True

            #Get [Certificate,] (if was requested)
            if reqCert:
                if self.version == (3,0):
                    for result in self._getMsg((ContentType.handshake,
                                               ContentType.alert),
                                               HandshakeType.certificate,
                                               certificateType):
                        if result in (0,1):
                            yield result
                        else:
                            break
                    msg = result

                    if isinstance(msg, Alert):
                        #If it's not a no_certificate alert, re-raise
                        alert = msg
                        if alert.description != \
                                AlertDescription.no_certificate:
                            self._shutdown(False)
                            raise TLSRemoteAlert(alert)
                    elif isinstance(msg, Certificate):
                        clientCertificate = msg
                        if clientCertificate.certChain and \
                                clientCertificate.certChain.getNumCerts()!=0:
                            clientCertChain = clientCertificate.certChain
                    else:
                        raise AssertionError()
                elif self.version in ((3,1), (3,2)):
                    for result in self._getMsg(ContentType.handshake,
                                              HandshakeType.certificate,
                                              certificateType):
                        if result in (0,1):
                            yield result
                        else:
                            break
                    clientCertificate = result
                    if clientCertificate.certChain and \
                            clientCertificate.certChain.getNumCerts()!=0:
                        clientCertChain = clientCertificate.certChain
                else:
                    raise AssertionError()

            #Get ClientKeyExchange
            for result in self._getMsg(ContentType.handshake,
                                      HandshakeType.client_key_exchange,
                                      cipherSuite):
                if result in (0,1):
                    yield result
                else:
                    break
            clientKeyExchange = result

            #Decrypt ClientKeyExchange
            premasterSecret = privateKey.decrypt(\
                clientKeyExchange.encryptedPreMasterSecret)

            randomPreMasterSecret = getRandomBytes(48)
            versionCheck = (premasterSecret[0], premasterSecret[1])
            if not premasterSecret:
                premasterSecret = randomPreMasterSecret
            elif len(premasterSecret)!=48:
                premasterSecret = randomPreMasterSecret
            elif versionCheck != clientHello.client_version:
                if versionCheck != self.version: #Tolerate buggy IE clients
                    premasterSecret = randomPreMasterSecret

            #Get and check CertificateVerify, if relevant
            if clientCertChain:
                if self.version == (3,0):
                    #Create a temporary session object, just for the purpose
                    #of checking the CertificateVerify
                    session = Session()
                    session._calcMasterSecret(self.version, premasterSecret,
                                             clientRandom, serverRandom)
                    verifyBytes = self._calcSSLHandshakeHash(\
                                    session.masterSecret, "")
                elif self.version in ((3,1), (3,2)):
                    verifyBytes = stringToBytes(self._handshake_md5.digest() +\
                                                self._handshake_sha.digest())
                for result in self._getMsg(ContentType.handshake,
                                          HandshakeType.certificate_verify):
                    if result in (0,1):
                        yield result
                    else:
                        break
                certificateVerify = result
                publicKey = clientCertChain.getEndEntityPublicKey()
                if len(publicKey) < settings.minKeySize:
                    postFinishedError = (AlertDescription.handshake_failure,
                        "Client's public key too small: %d" % len(publicKey))
                if len(publicKey) > settings.maxKeySize:
                    postFinishedError = (AlertDescription.handshake_failure,
                        "Client's public key too large: %d" % len(publicKey))

                if not publicKey.verify(certificateVerify.signature,