tlslite-ng version 0.8.0 (2024-12-17)

Table of Contents

1. Introduction
2. License/Acknowledgements
3. Installation
4. Getting Started with the Command-Line Tools
5. Getting Started with the Library
6. Using tlslite-ng with httplib
7. Using tlslite-ng with poplib or imaplib
8. Using tlslite-ng with smtplib
9. Using tlslite-ng with SocketServer
10. Using tlslite-ng with asyncore
11. History

1 Introduction

tlslite-ng is an open source python library that implements SSL and TLS cryptographic protocols. It can be used either as a standalone wrapper around python socket interface or as a backend for multiple other libraries. tlslite-ng is pure python, however it can use other libraries for faster crypto operations. tlslite-ng integrates with several stdlib networking libraries.

API documentation is available in the docs/_build/html directory of the PyPI package or can be automatically generated using make docs with Sphinx installed.

If you have questions or feedback, feel free to contact me (Alicja Kario <hkario at redhat.com>). Issues and pull requests can also be submitted through github issue tracking system, at the project's main page at GitHub, see CONTRIBUTING.md file for more information.

tlslite-ng aims to be a drop in replacement for the original TLS Lite.

Security policy of the project is available in the SECURITY.md file.

Implemented TLS features include:

• SSLv3, TLSv1.0, TLSv1.1, TLSv1.2 and TLSv1.3
• ciphersuites with DHE, ADH, ECDHE, AECDH, ML-KEM, RSA and SRP key exchange together with AES (CBC, GCM, CCM and CCM_8), 3DES, RC4 and ChaCha20 (both the official standard and the IETF draft) symmetric ciphers and NULL encryption.
• PSK and PSK-(EC)DHE key exchange in TLSv1.3
• Secure Renegotiation
• Encrypt Then MAC extension
• TLS_FALLBACK_SCSV
• Extended master secret
• padding extension
• keying material exporter
• RSA, RSA-PSS, DSA, ECDSA, and EdDSA certificates
• ticket based session resumption
• 1-RTT handshake, Hello Retry Request, middlebox compatibility mode, cookie extension, post-handshake authentication and KeyUpdate (TLS 1.3)
• FFDHE supported_groups extension
• X25519 and X448 ECDHE key exchange
• Ed25519 and Ed448 EdDSA signatures
• (experimental) TACK extension
• heartbeat extension and protocol
• Record Size Limit extension

2 Licenses/Acknowledgements

tlslite-ng is a fork of TLS Lite, it is currently maintained and developed by Alicja Kario. TLS Lite was written (mostly) by Trevor Perrin. It includes code from Bram Cohen, Google, Kees Bos, Sam Rushing, Dimitris Moraitis, Marcelo Fernandez, Martin von Loewis, Dave Baggett, Yngve N. Pettersen (ported by Paul Sokolovsky), Mirko Dziadzka, David Benjamin, Sidney Markowitz, and Alicja Kario.

Original code in TLS Lite has either been dedicated to the public domain by its authors, or placed under a BSD-style license. See the LICENSE file for details.

Currently it is distributed under Gnu LGPLv2 license.

3 Installation

Requirements:

• Python 2.6 or higher is required.
• Python 3.6 or higher is supported.
• python ecdsa >= 0.13.3 library (GitHub, PyPI)

Options:

• If you have the m2crypto interface to OpenSSL, this will be used for fast RSA operations and fast ciphers.
• If you have pycrypto this will be used for fast RSA operations and fast ciphers.
• If you have the gmpy interface to libgmp, this will be used for fast RSA, FFDH and SRP operations.
• These modules don't need to be present at installation - you can install them any time.

3.1 Automatic

Run:

pip install tlslite-ng

In case your system doesn't have pip, you can install it by first downloading get-pip.py and running

python get-pip.py

3.2 Manual

Run 'python setup.py install'

Test the Installation

• From the distribution's directory, run:

  make test
  

• If it says "Test succeeded" at the end, you're ready to go.

4 Getting Started with the Command-Line Tools

tlslite-ng installs two command-line scripts: tlsdb.py and tls.py.

tls.py lets you run test clients and servers. It can be used for testing other TLS implementations, or as example code. Note that tls.py server runs an HTTPS server which will serve files rooted at the current directory by default, so be careful.

tlsdb.py lets you manage SRP verifier databases. These databases are used by a TLS server when authenticating clients with SRP.

X.509

To run an X.509 server, go to the ./tests directory and do:

tls.py server -k serverX509Key.pem -c serverX509Cert.pem localhost:4443

Try connecting to the server with a web browser, or with:

tls.py client localhost:4443

X.509 with TACK

To run an X.509 server using a TACK, install TACKpy, then run the same server command as above with added arguments:

... -t TACK1.pem localhost:4443

SRP

To run an SRP server, try something like:

tlsdb.py createsrp verifierDB
tlsdb.py add verifierDB alice abra123cadabra 1024
tlsdb.py add verifierDB bob swordfish 2048

tls.py server -v verifierDB localhost:4443

Then try connecting to the server with:

tls.py client -u alice -p abra123cadabra localhost:4443

HTTPS

To run an HTTPS server with less typing, run ./tests/httpsserver.sh.

To run an HTTPS client, run ./tests/httpsclient.py.

5 Getting Started with the Library

Whether you're writing a client or server, there are six steps:

1. Create a socket and connect it to the other party.
2. Construct a TLSConnection instance with the socket.
3. Call a handshake function on TLSConnection to perform the TLS handshake.
4. Check the results to make sure you're talking to the right party.
5. Use the TLSConnection to exchange data.
6. Call close() on the TLSConnection when you're done.

tlslite-ng also integrates with several stdlib python libraries. See the sections following this one for details.

5 Step 1 - create a socket

Below demonstrates a socket connection to Amazon's secure site.

  from socket import *
  sock = socket(AF_INET, SOCK_STREAM)
  sock.connect( ("www.amazon.com", 443) )

5 Step 2 - construct a TLSConnection

You can import tlslite objects individually, such as:

  from tlslite import TLSConnection

Or import the most useful objects through:

  from tlslite.api import *

Then do:

  connection = TLSConnection(sock)

5 Step 3 - call a handshake function (client)

If you're a client, there's two different handshake functions you can call, depending on how you want to authenticate:

  connection.handshakeClientCert()
  connection.handshakeClientCert(certChain, privateKey)

  connection.handshakeClientSRP("alice", "abra123cadabra")

The ClientCert function without arguments is used when connecting to a site like Amazon, which doesn't require client authentication, but which will authenticate itself using an X.509 certificate chain.

The ClientCert function can also be used to do client authentication with an X.509 certificate chain and corresponding private key. To use X.509 chains, you'll need some way of creating these, such as OpenSSL (see HOWTO for details).

Below is an example of loading an X.509 chain and private key:

  from tlslite import X509, X509CertChain, parsePEMKey
  s = open("./test/clientX509Cert.pem").read()
  x509 = X509()
  x509.parse(s)
  certChain = X509CertChain([x509])
  s = open("./test/clientX509Key.pem").read()
  privateKey = parsePEMKey(s, private=True)

The SRP function does mutual authentication with a username and password - see RFC 5054 for details.

If you want more control over the handshake, you can pass in a HandshakeSettings instance. For example, if you're performing SRP, but you only want to use SRP parameters of at least 2048 bits, and you only want to use the AES-256 cipher, and you only want to allow TLS (version 3.1), not SSL (version 3.0), you can do:

  settings = HandshakeSettings()
  settings.minKeySize = 2048
  settings.cipherNames = ["aes256"]
  settings.minVersion = (3,1)
  settings.useExperimentalTACKExtension = True  # Needed for TACK support

  connection.handshakeClientSRP("alice", "abra123cadabra", settings=settings)

If you want to check the server's certificate using TACK, you should set the "useExperiementalTACKExtension" value in HandshakeSettings. (Eventually, TACK support will be enabled by default, but for now it is an experimental feature which relies on a temporary TLS Extension number, and should not be used for production software.) This will cause the client to request the server to send you a TACK (and/or any TACK Break Signatures):

Finally, every TLSConnection has a session object. You can try to resume a previous session by passing in the session object from the old session. If the server remembers this old session and supports resumption, the handshake will finish more quickly. Otherwise, the full handshake will be done. For example:

  connection.handshakeClientSRP("alice", "abra123cadabra")
  .
  .
  oldSession = connection.session
  connection2.handshakeClientSRP("alice", "abra123cadabra", session=
  oldSession)

5 Step 3 - call a handshake function (server)

If you're a server, there's only one handshake function, but you can pass it several different parameters, depending on which types of authentication you're willing to perform.

To perform SRP authentication, you have to pass in a database of password verifiers. The VerifierDB class manages an in-memory or on-disk verifier database.

  verifierDB = VerifierDB("./test/verifierDB")
  verifierDB.open()
  connection.handshakeServer(verifierDB=verifierDB)

To perform authentication with a certificate and private key, the server must load these as described in the previous section, then pass them in. If the server sets the reqCert boolean to True, a certificate chain will be requested from the client.

  connection.handshakeServer(certChain=certChain, privateKey=privateKey,
                             reqCert=True)

You can pass in a verifier database and/or a certificate chain+private key. The client will use one or both to authenticate the server.

You can also pass in a HandshakeSettings object, as described in the last section, for finer control over handshaking details.

If you are passing in a certificate chain+private key, you may additionally provide a TACK to assist the client in authenticating your certificate chain. This requires the TACKpy library. Load a TACKpy.TACK object, then do:

  settings = HandshakeSettings()
  settings.useExperimentalTACKExtension = True  # Needed for TACK support

  connection.handshakeServer(certChain=certChain, privateKey=privateKey,
                             tack=tack, settings=settings)

Finally, the server can maintain a SessionCache, which will allow clients to use session resumption:

  sessionCache = SessionCache()
  connection.handshakeServer(verifierDB=verifierDB, sessionCache=sessionCache)

It should be noted that the session cache, and the verifier databases, are all thread-safe.

5 Step 4 - check the results

If the handshake completes without raising an exception, authentication results will be stored in the connection's session object. The following variables will be populated if applicable, or else set to None:

  connection.session.srpUsername       # string
  connection.session.clientCertChain   # X509CertChain
  connection.session.serverCertChain   # X509CertChain
  connection.session.tackExt           # TACKpy.TACK_Extension

X.509 chain objects return the end-entity fingerprint via getFingerprint(), and ignore the other certificates.

TACK objects return the (validated) TACK ID via getTACKID().

To save yourself the trouble of inspecting certificates after the handshake, you can pass a Checker object into the handshake function. The checker will be called if the handshake completes successfully. If the other party isn't approved by the checker, a subclass of TLSAuthenticationError will be raised.

If the handshake fails for any reason, including a Checker error, an exception will be raised and the socket will be closed. If the socket timed out or was unexpectedly closed, a socket.error or TLSAbruptCloseError will be raised.

Otherwise, either a TLSLocalAlert or TLSRemoteAlert will be raised, depending on whether the local or remote implementation signalled the error. The exception object has a 'description' member which identifies the error based on the codes in RFC 2246. A TLSLocalAlert also has a 'message' string that may have more details.

Example of handling a remote alert:

  try:
      [...]
  except TLSRemoteAlert as alert:
      if alert.description == AlertDescription.unknown_psk_identity:
          print "Unknown user."
  [...]

Below are some common alerts and their probable causes, and whether they are signalled by the client or server.

Client handshake_failure:

• SRP parameters are not recognized by client
• Server's TACK was unrelated to its certificate chain

Client insufficient_security:

• SRP parameters are too small

Client protocol_version:

• Client doesn't support the server's protocol version

Server protocol_version:

• Server doesn't support the client's protocol version

Server bad_record_mac:

• bad SRP username or password

Server unknown_psk_identity:

• bad SRP username (bad_record_mac could be used for the same thing)

Server handshake_failure:

• no matching cipher suites

5 Step 5 - exchange data

Now that you have a connection, you can call read() and write() as if it were a socket.SSL object. You can also call send(), sendall(), recv(), and makefile() as if it were a socket. These calls may raise TLSLocalAlert, TLSRemoteAlert, socket.error, or TLSAbruptCloseError, just like the handshake functions.

Once the TLS connection is closed by the other side, calls to read() or recv() will return an empty string. If the socket is closed by the other side without first closing the TLS connection, calls to read() or recv() will return a TLSAbruptCloseError, and calls to write() or send() will return a socket.error.

5 Step 6 - close the connection

When you're finished sending data, you should call close() to close the connection and socket. When the connection is closed properly, the session object can be used for session resumption.

If an exception is raised the connection will be automatically closed; you don't need to call close(). Furthermore, you will probably not be able to re-use the socket, the connection object, or the session object, and you shouldn't even try.

By default, calling close() will close the underlying socket. If you set the connection's closeSocket flag to False, the socket will remain open after close. (NOTE: some TLS implementations will not respond properly to the close_notify alert that close() generates, so the connection will hang if closeSocket is set to True.)

6 Using tlslite-ng with httplib

tlslite-ng comes with an HTTPTLSConnection class that extends httplib to work over SSL/TLS connections. Depending on how you construct it, it will do different types of authentication.

  #No authentication whatsoever
  h = HTTPTLSConnection("www.amazon.com", 443)
  h.request("GET", "")
  r = h.getresponse()
  [...]

  #Authenticate server based on its TACK ID
  h = HTTPTLSConnection("localhost", 4443,
          tackID="B3ARS.EQ61B.F34EL.9KKLN.3WEW5", hardTack=False)
  [...]

  #Mutually authenticate with SRP
  h = HTTPTLSConnection("localhost", 443,
          username="alice", password="abra123cadabra")
  [...]

7 Using tlslite-ng with poplib or imaplib

tlslite-ng comes with POP3_TLS and IMAP4_TLS classes that extend poplib and imaplib to work over SSL/TLS connections. These classes can be constructed with the same parameters as HTTPTLSConnection (see previous section), and behave similarly.

  #To connect to a POP3 server over SSL and display its fingerprint:
  from tlslite.api import *
  p = POP3_TLS("---------.net", port=995)
  print p.sock.session.serverCertChain.getFingerprint()
  [...]

  #To connect to an IMAP server once you know its fingerprint:
  from tlslite.api import *
  i = IMAP4_TLS("cyrus.andrew.cmu.edu",
          x509Fingerprint="00c14371227b3b677ddb9c4901e6f2aee18d3e45")
  [...]

8 Using tlslite-ng with smtplib

tlslite-ng comes with an SMTP_TLS class that extends smtplib to work over SSL/TLS connections. This class accepts the same parameters as HTTPTLSConnection (see previous section), and behaves similarly. Depending on how you call starttls(), it will do different types of authentication.

  #To connect to an SMTP server once you know its fingerprint:
  from tlslite.api import *
  s = SMTP_TLS("----------.net", port=587)
  s.ehlo()
  s.starttls(x509Fingerprint="7e39be84a2e3a7ad071752e3001d931bf82c32dc")
  [...]

9 Using tlslite-ng with SocketServer

You can use tlslite-ng to implement servers using Python's SocketServer framework. tlslite-ng comes with a TLSSocketServerMixIn class. You can combine this with a TCPServer such as HTTPServer. To combine them, define a new class that inherits from both of them (with the mix-in first). Then implement the handshake() method, doing some sort of server handshake on the connection argument. If the handshake method returns True, the RequestHandler will be triggered. See the tests/httpsserver.py example.

10 Using tlslite-ng with asyncore (or asyncio - Python 3.12+)

tlslite-ng can be used with subclasses of asyncore.dispatcher. See the comments in TLSAsyncDispatcherMixIn.py for details. This is still experimental, and may not work with all asyncore.dispatcher subclasses.

as said above, asyncore is deprecated in Python 3.12, and asyncio should be used. Implementation is similar to TLSAsyncDispatcherMixIn.py, but instead, use the class TLSAsyncioDispatcherMixIn.py.

11 History

0.8.0 - 2024-12-17

• DEPRECATION NOTICE: camelCase method and argument names are considered now deprecated, ones that use underscore_separator are now the primary ones (the procedure to support it is not yet finished, but any new code must follow this new style and new deprecations will be introduced as time goes on. Please run your test suite with -Wd to see where the depracated calls are being made, the python standard DeprecationWarning will be emited there)
• Python 3.2, 3.3, and 3.4 is not supported any more (dropped by python-ecdsa)
• fix compatibility issue with 8192 bit SRP group from RFC 5054
• fix CVE-2018-1000159 - incorrect verification of MAC in MAC then Encrypt mode
• workaround CVE-2020-26263 - Bleichenbacher oracle in RSA decryption. Please note that while the code was fortified, because of peculiarities of python, it's not possible to fully fix it. If you require resistance against side-channel attacks please use a different library.
• fix Python_RSAKey multithreading support - performing private key operation in two threads at the same time could make all future calls return incorrect results
• Python 3.7 support (async is now a keyword) (Pierre Ståhl)
• Python 3.8 test suite compatibility
• Python 3.9 support (slight changes in imaplib caused our wrapper to stop working)
• Compatibility with M2Crypto on Python 3
• fix Python 2 comaptibility issue with X.509 DER parsing (Erkki Vahala)
• TLS 1.3
  • final RFC 8446 support
  • TLS 1.3 specific ciphers (AES-GCM, AES-CCM, AES-CCM8 and Chacha20)
  • TLS 1.3 specific extensions and extension code points
  • 1-RTT handshake mode
  • HelloRetryRequest support
  • PSK with (EC)DH key exchange
  • pure PSK
  • session resumption in TLS 1.3 using PSK tickets
  • padding support (Stanislav Zidek)
  • 0-RTT handshake tolerance (the early data will be ignored but handshake will succeed)
  • cookie extension
  • downgrade sentinels in ServerHello.random
  • TLS Keying Material Exporter support in TLS 1.3 (Simo Sorce)
  • client certificate support (Simo Sorce)
  • KeyUpdate support
  • post-handshake key authentication
• fix minor compatibility issue with Jython2.7 (Filip Goldefus)
• higher precision of throughput measurement on non-Linux platforms (Efthimis Iosifidis)
• refactor keyexchange.py module to make (EC)DH key exchange standalone
• more human readable errors upon receiving unexpected messages
• __eq__ supported on all Handshake messages
• fix minor bugs in message objects, extend test coverage for tlslite.messages
• repr() for Certificate and few extensions
• OCSP response parsing (Anna Khaitovich)
• OCSP signature verification (Anna Khaitovich)
• matching OCSP response to EE and CA certificate (Anna Khaitovich)
• fix HTTP header length leak in the test server (tls.py) (Róbert Kolcún)
• minor fixes with sent alerts when encountering error conditions
• fix lack of checking if the padding in SSLv3 is minimal
• Pure Python 3DES implementation (Adam Varga)
• heartbeat (RFC 6520) (Milan Lysonek)
• support chain of certificates in the tls.py script
• fix sending of RSA-PSS certificate when the client didn't advertise support for rsa_pss_pss_* signature methods
• clearly state in documentation that inputs to signature and verification methods of RSA keys need to be bytes-like objects
• support for setting maximum supported version in tls.py server and client
• support for record_size_limit extension from RFC 8449
• make the number of session tickets sent to client configurable (TLS 1.3 specific)
• reimplement HMAC in pure python to work-around platforms that disable MD5 HMAC in python (this goes against FIPS requirements)
• fix few minor bugs in handling heartbeat messages
• support for ECDSA certificates (server and client, all versions of TLS)
• support for multiple certificates on the server (RSA, RSA-PSS, ECDSA can be configured together, including multiple instances of the same type, server will select automatically the one that matches requirements from ClientHello)
• support for HelloRequest messages (only for encoding/decoding, renegotiation is still unsupported)
• nicer error messages when parsing malformed exceptions, TLS messages in general
• AES-CCM and AES-CCM8 support (in TLS 1.2 and TLS 1.3) (Ivan Nikolchev)
• added support for configuring enabled ciphers in tls.py (Ivan Nikolchev)
• two times faster 3DES when using m2crypto (Alexander Sosedkin)
• correct handling of malformed X.509 certificates (Ivan Nikolchev)
• speed up AES-CCM and AES-GCM when m2crypto is installed (Ivan Nikolchev)
• client side checks for downgrade protection from TLS 1.3 (Ivan Nikolchev)
• use TLS 1.3 test vectors to verify the implementation (Ivan Nikolchev)
• unify master secret and finished calculation (Ivan Nikolchev)
• detect pycryptodome, disable pycrypto code if it's present
• add multiple well-known DH groups from RFC 2409, RFC 5114 and RFC 3526, unify formatting of the existing DH group (use exactly the formatting used in the RFC's)
• add benchmarking tool for RSA (scripts/speed.py)
• add support for gmpy2, use it and gmpy in more places for RSA calculations (minor speed up for RSA operations)
• refactor certificate selection, make server select certificate based on curves and signature algorithms advertised by client (Ivan Nikolchev)
• basic support for DSA certificates; verification of DSA signatures in ServerKeyExchange (Frantisek Krenzelok)
• support for DSA client certificates
• small optimisations to PRF methods, speeds to handshake
• support for MD5 signatures in X.509 certificates (Jean-Romain Garnier)
• add support for Brainpool curves in TLS 1.2 and earlier (pytz)
• fix wrong error message in AES implementation (Bernt Røskar Brenna)
• migrate to Github Action for CI
• fix API break caused by the workaround for Bleichenbacher; RSA keys generated in-memory with m2crypto wouldn't work for decryption/encryption
• handle too short RSA ciphertexts for the key size consistently between backends
• strict handling of CCS in TLS 1.3 (don't allow it post handshake)
• detect and reject multi-byte CCS messages
• improved RSA key generation - don't generate biased primes
• support for both encodings of RSA-PSS algorithm identifier in X.509
• Support for EdDSA (Ed25519 and Ed448) in TLS 1.2 and TLS 1.3, both for server and client certificates
• Support for echo server in the example tls.py script
• Better handling of HMACs in FIPS mode
• Generate RSA keys with 65537 as public exponent with m2crypto (as with other backends)
• Ticket based session resumption in TLS 1.2 and earlier
• strict size checking of session_id field in ClientHello
• use python-ecdsa code for parsing ECDH key shares, speed up calculation of shared secrets (Ganna Starovoytova)
• fix sending of session ticket extension from the server without a ticket (George Pantelakis)
• add support for Brainpool curves in TLS 1.3 from RFC 8734
• add support for compress_certificate extension from RFC 8879 (George Pantelakis)
• Fix int_to_bytes and numberToByteArray encoding of 0 with length not specified, and thus also ClientKeyExchange handling for DHE with missing key share
• (Experimental) Support for hybrid KEM key exchange groups from draft-kwiatkowski-tls-ecdhe-mlkem-02. To work, kyber-py v1.0 library must be installed.
• support for setting a list of supported key exchange groups in the tls.py server
• support for ec_point_format extension (Ganna Starovoytova)

0.7.0 - 2017-07-31

• enable and add missing definitions of TLS_ECDHE_RSA_WITH_RC4_128_SHA and TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA
• add definitions of some ECDHE_ECDSA, ECDH_ECDSA and ECDH_RSA ciphersuites, they remain unsupported, but IDs are useful for other projects
• basic support for RSA-PSS (Tomas Foukal)
• support for RSA-PSS in TLSv1.2
• better documentation for Parser and ASN1Parser
• stricter checks on network messages
• faster Codec (faster encoding of messages to binary format)
• faster AES implementation initialization
• ability to set custom Diffie-Hellman parameters for connection
• support for negotiation of bigger Diffie-Hellman groups using RFC 7919 mechanism
• fix sent alerts in case the ALPN extension is malformed
• add support for checking SNI on server side, making sure we send valid hostnames in extension
• fix testsuite when run on Windows
• fix interoperability issue in DHE key exchange (failure happening in about 1 in 256 negotiations) caused by handling of Server Key Exchange messages
• Fix incorrect handling of Extended Master Secret with client certificates, follow RFC recommendations with regards to session resumption, reject non-empty
• Allow negotiation of ECDHE ciphersuites even if client doesn't advertise any curves, default to P-256 curve support, support configuring the default
• Stricter checks on received SNI (server_name) extension
• Support for x25519 and x448 curve for ECDHE

0.6.0 - 2016-09-07

• added support for ALPN from RFC 7301
• fixed handling of SRP databases
• fixed compatibility issues with Python 3
• fixed compatibility with Python 2.7.3
• AECDH support on server side (Milan Lysonek)
• make the Client Hello parser more strict, it will now abort if the extensions extend past the length of extension field
• make the decoder honour the 2^14 byte protocol limit on plaintext per record
• fix sending correct alerts on receiving malformed or invalid messages in handshake
• proper signalling for Secure Renegotiation (renegotiation remains unsupported but server now indicates that the extension was understood and will abort if receiving a renegotiated hello)
• stop server from leaking lengths of headers in HTTP responses when using standard library modules
• HMAC-based Extract-and-Expand Key Derivation Function (HKDF) implementation from RFC 5869 (Tomas Foukal)
• added protection against RSA-CRT key leaks (Tomas Foukal)
• Keying material exporter from RFC 5705
• Session Hash a.k.a. Extended Master Secret extension from RFC 7627
• make the library work on systems working in FIPS mode
• support for the padding extension from RFC 7685 (Karel Srot)
• abitlity to perform reverse lookups on many of the TLS type enumerations
• added ECDHE_RSA key exchange together with associated ciphersuites
• refactor key exchange code to remove duplication and make adding new methods easier
• add support for all hashes for ServerKeyExchange and CertificateVerify messages in TLS 1.2
• mark library as compatible with Python 3.5 (it was previously, but now it is verified with Continous Integration)
• cleanups (style fixes, deduplication of code) and more documentation
• add support for ChaCha20 and Poly1305 (both the IETF draft and released standard) with both ECDHE_RSA and DHE_RSA key exchange
• expose padding and MAC-ing functions and blockSize property in RecordLayer

0.5.1 - 2015-11-05

• fix SRP_SHA_RSA ciphersuites in TLSv1.2 (for real this time)
• minor enchancements in test scripts
• NOTE: KeyExchange class is not part of stable API yet (it will be moved to different module later)!

0.5.0 - 10/10/2015

• fix generators in AsyncStateMachine to work on Python3 (Theron Lewis)
• fix CVE-2015-3220 - remote DoS caused by incorrect malformed packet handling
• removed RC4 from ciphers supported by default
• add supported_groups, supported_point_formats, signature_algorithms and renegotiation_info extensions
• remove most CBC MAC-ing and padding timing side-channel leaks (should fix CVE-2013-0169, a.k.a. Lucky13)
• add support for NULL encryption - TLS_RSA_WITH_NULL_MD5, TLS_RSA_WITH_NULL_SHA and TLS_RSA_WITH_NULL_SHA256 ciphersuites
• add more ADH ciphers (TLS_DH_ANON_WITH_RC4_128_MD5, TLS_DH_ANON_WITH_3DES_EDE_CBC_SHA, TLS_DH_ANON_WITH_AES_128_CBC_SHA256, TLS_DH_ANON_WITH_AES_256_CBC_SHA256, TLS_DH_ANON_WITH_AES_128_GCM_SHA256, TLS_DH_ANON_WITH_AES_256_GCM_SHA384)
• implement a TLS record layer abstraction that makes it very easy to handle TLS handshake and alert protocol messages (MessageSocket)
• fix reqCert option in tls.py server
• implement AES-256-GCM ciphersuites and SHA384 PRF
• implement AES-GCM cipher and AES-128-GCM ciphersuites (David Benjamin - Chromium)
• implement client side DHE_RSA key exchange and DHE with certificate based client authentication
• implement server side DHE_RSA key exchange (David Benjamin - Chromium)
• don't use TLSv1.2 ciphers in earlier protocols (David Benjamin - Chromium)
• fix certificate-based client authentication in TLSv1.2 (David Benjamin - Chromium)
• fix SRP_SHA_RSA ciphersuites
• properly implement record layer fragmentation (previously worked just for Application Data) - RFC 5246 Section 6.2.1
• Implement RFC 7366 - Encrypt-then-MAC
• generate minimal padding for CBC ciphers (David Benjamin - Chromium)
• implementation of FALLBACK_SCSV (David Benjamin - Chromium)
• fix issue with handling keys in session cache (Mirko Dziadzka)
• coverage measurement for unit tests
• introduced Continous Integration, targetting 2.6, 2.7, 3.2, 3.3 and 3.4
• support PKCS#8 files with m2crypto installed for loading private keys
• fix Writer not to silently overflow integers
• fix Parser getFixBytes boundary checking
• big code refactors, mainly TLSRecordLayer and TLSConnection, lot of code put under unit test coverage

0.4.8 - 11/12/2014

• Added more acknowledgements and security considerations

0.4.7 - 11/12/2014

• Added TLS 1.2 support (Yngve Pettersen and Paul Sokolovsky)
• Don't offer SSLv3 by default (e.g. POODLE)
• Fixed bug with PyCrypto_RSA integration
• Fixed harmless bug that added non-prime into sieves list
• Added "make test" and "make test-dev" targets (Alicja Kario)

0.4.5 - 3/20/2013

• API CHANGE: TLSClosedConnectionError instead of ValueError when writing to a closed connection. This inherits from socket.error, so should interact better with SocketServer (see issue14574) and other things expecting a socket.error in this situation.
• Added support for RC4-MD5 ciphersuite (if enabled in settings)
  • This is allegedly necessary to connect to some Internet servers.
• Added TLSConnection.unread() function
• Switched to New-style classes (inherit from 'object')
• Minor cleanups

0.4.4 - 2/25/2013

• Added Python 3 support (Martin von Loewis)
• Added NPN client support (Marcelo Fernandez)
• Switched to RC4 as preferred cipher
  • faster in Python, avoids "Lucky 13" timing attacks
• Fixed bug when specifying ciphers for anon ciphersuites
• Made RSA hashAndVerify() tolerant of sigs w/o encoded NULL AlgorithmParam
  • (this function is not used for TLS currently, and this tolerance may not even be necessary)

0.4.3 - 9/27/2012

• Minor bugfix (0.4.2 doesn't load tackpy)

0.4.2 - 9/25/2012

• Updated TACK (compatible with tackpy 0.9.9)

0.4.1 - 5/22/2012

• Fixed RSA padding bugs (w/help from John Randolph)
• Updated TACK (compatible with tackpy 0.9.7)
• Added SNI
• Added NPN server support (Sam Rushing/Google)
• Added AnonDH (Dimitris Moraitis)
• Added X509CertChain.parsePemList
• Improved XML-RPC (Kees Bos)

0.4.0 - 2/11/2012

• Fixed pycrypto support
• Fixed python 2.6 problems

0.3.9.x - 2/7/2012

Much code cleanup, in particular decomposing the handshake functions so they are readable. The main new feature is support for TACK, an experimental authentication method that provides a new way to pin server certificates (See moxie0/Convergance ).

Also:

• Security Fixes

  • Sends SCSV ciphersuite as per RFC 5746, to signal non-renegotiated Client Hello. Does not support renegotiation (never has).
  • Change from e=3 to e=65537 for generated RSA keys, not strictly necessary but mitigates risk of sloppy verifier.
  • 1/(n-1) countermeasure for BEAST.

• Behavior changes:

  • Split cmdline into tls.py and tlstest.py, improved options.
  • Formalized LICENSE.
  • Defaults to closing socket after sending close_notify, fixes hanging. problem that would occur sometime when waiting for other party's close_notify.
  • Update SRP to RFC 5054 compliance.
  • Removed client handshake "callbacks", no longer support the SRP re-handshake idiom within a single handshake function.

• Bugfixes

  • Added hashlib support, removes Deprecation Warning due to sha and md5.
  • Handled GeneratorExit exceptions that are a new Python feature, and interfere with the async code if not handled.

• Removed:

  • Shared keys (it was based on an ancient I-D, not TLS-PSK).
  • cryptlib support, it wasn't used much, we have enough other options.
  • cryptoIDs (TACK is better).
  • win32prng extension module, as os.urandom is now available.
  • Twisted integration (unused?, slowed down loading).
  • Jython code (ancient, didn't work).
  • Compat support for python versions < 2.7.

• Additions

  • Support for TACK via TACKpy.
  • Support for CertificateRequest.certificate_authorities ("reqCAs")
  • Added TLSConnection.shutdown() to better mimic socket.
  • Enabled Session resumption for XMLRPCTransport.

0.3.8 - 2/21/2005

• Added support for poplib, imaplib, and smtplib
• Added python 2.4 windows installer
• Fixed occassional timing problems with test suite

0.3.7 - 10/05/2004

• Added support for Python 2.2
• Cleaned up compatibility code, and docs, a bit

0.3.6 - 9/28/2004

• Fixed script installation on UNIX
• Give better error message on old Python versions

0.3.5 - 9/16/2004

• TLS 1.1 support
• os.urandom() support
• Fixed win32prng on some systems

0.3.4 - 9/12/2004

• Updated for TLS/SRP draft 8
• Bugfix: was setting _versioncheck on SRP 1st hello, causing problems with GnuTLS (which was offering TLS 1.1)
• Removed _versioncheck checking, since it could cause interop problems
• Minor bugfix: when cryptlib_py and and cryptoIDlib present, cryptlib was complaining about being initialized twice

0.3.3 - 6/10/2004

• Updated for TLS/SRP draft 7
• Updated test cryptoID cert chains for cryptoIDlib 0.3.1

0.3.2 - 5/21/2004

• fixed bug when handling multiple handshake messages per record (e.g. IIS)

0.3.1 - 4/21/2004

• added xmlrpclib integration
• fixed hanging bug in Twisted integration
• fixed win32prng to work on a wider range of win32 sytems
• fixed import problem with cryptoIDlib
• fixed port allocation problem when test scripts are run on some UNIXes
• made tolerant of buggy IE sending wrong version in premaster secret

0.3.0 - 3/20/2004

• added API docs thanks to epydoc
• added X.509 path validation via cryptlib
• much cleaning/tweaking/re-factoring/minor fixes

0.2.7 - 3/12/2004

• changed Twisted error handling to use connectionLost()
• added ignoreAbruptClose

0.2.6 - 3/11/2004

• added Twisted errorHandler
• added TLSAbruptCloseError
• added 'integration' subdirectory

0.2.5 - 3/10/2004

• improved asynchronous support a bit
• added first-draft of Twisted support

0.2.4 - 3/5/2004

• cleaned up asyncore support
• added proof-of-concept for Twisted

0.2.3 - 3/4/2004

• added pycrypto RSA support
• added asyncore support

0.2.2 - 3/1/2004

• added GMPY support
• added pycrypto support
• added support for PEM-encoded private keys, in pure python

0.2.1 - 2/23/2004

• improved PRNG use (cryptlib, or /dev/random, or CryptoAPI)
• added RSA blinding, to avoid timing attacks
• don't install local copy of M2Crypto, too problematic

0.2.0 - 2/19/2004

• changed VerifierDB to take per-user parameters
• renamed tls_lite -> tlslite

0.1.9 - 2/16/2004

• added post-handshake 'Checker'
• made compatible with Python 2.2
• made more forgiving of abrupt closure, since everyone does it: if the socket is closed while sending/recv'ing close_notify, just ignore it.

0.1.8 - 2/12/2004

• TLSConnections now emulate sockets, including makefile()
• HTTPTLSConnection and TLSMixIn simplified as a result

0.1.7 - 2/11/2004

• fixed httplib.HTTPTLSConnection with multiple requests
• fixed SocketServer to handle close_notify
• changed handshakeClientNoAuth() to ignore CertificateRequests
• changed handshakeClient() to ignore non-resumable session arguments

0.1.6 - 2/10/2004

• fixed httplib support

0.1.5 - 2/09/2004

• added support for httplib and SocketServer
• added support for SSLv3
• added support for 3DES
• cleaned up read()/write() behavior
• improved HMAC speed

0.1.4 - 2/06/2004

• fixed dumb bug in tls.py

0.1.3 - 2/05/2004

• change read() to only return requested number of bytes
• added support for shared-key and in-memory databases
• added support for PEM-encoded X.509 certificates
• added support for SSLv2 ClientHello
• fixed shutdown/re-handshaking behavior
• cleaned up handling of missing_srp_username
• renamed readString()/writeString() -> read()/write()
• added documentation

0.1.2 - 2/04/2004

• added clienttest/servertest functions
• improved OpenSSL cipher wrappers speed
• fixed server when it has a key, but client selects plain SRP
• fixed server to postpone errors until it has read client's messages
• fixed ServerHello to only include extension data if necessary

0.1.1 - 2/02/2004

• fixed close_notify behavior
• fixed handling of empty application data packets
• fixed socket reads to not consume extra bytes
• added testing functions to tls.py

0.1.0 - 2/01/2004

• first release