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Dissononce

Dissononce is a python implementation for Noise Protocol Framework. A main goal of this project is to provide a simple, easy to read and understand practical reference for Noise enthusiasts, implementers and users. Therefore this project attempts to stick to the following guidelines:

• Syntax that resembles as closely as possible definitions and pseudo code mentioned in Noise Specs.
• As minimal python "magic" as possible (explicit is better than implicit).
• Code that is simple, easy to read, follow and understand.
• Flexibility to easily adopt future changes to Noise specifications.
• Deviations from Noise Specs (additions, opinionated specs and API changes..etc) are isolated from original implementation/API and are optional to use.
• Deviations from Noise Specs do not influence adjustments to original implementation/API that conflict with Noise Specs.

META-INF

dissononce version: 0.34.3
noise revision: 34
released: 2019-04-24
requires:
- python>=2.5,<=3.7
- cryptography>=2.5
uses:
- transitions==0.6.9

Contents

• Installation
• Usage
  • Crypto Functions
  • Processing
  • Handshake Patterns
  • Modifiers
  • Extras
    • Crypto functions by name
    • Noise Protocol by name
    • GuardedHandshakeState
    • SwitchableHandshakeState
    • NoGenDH
• Examples
• Testing
• Logging
• Appendices

Installation

From source:

python setup.py install

Using Pip:

pip install dissononce

Usage

Crypto Functions

Each set of Crypto functions (DH, Cipher, Hash) is enclosed inside an own base class, where an implementation subclasses that base class to implement the methods.

• DH-functions base class: dissononce.dh.dh.DH
• Cipher-functions base class: dissononce.cipher.cipher.Cipher
• Hash-functions base class: dissononce.hash.hash.Hash

Example instantiating objects for X25519 DH, AESGCM Cipher and SHA256 Hash:

from dissononce.cipher.aesgcm import AESGCMCipher
from dissononce.dh.x25519.x25519 import X25519DH
from dissononce.hash.sha256 import SHA256Hash

cipher = AESGCMCipher()
dh = X25519DH()
hash = SHA256Hash()

Implementations for each set of crypto functions are organized according to their support level:

• stable: officially covered in Noise spec, accessible under:
  • dissononce/dh/
  • dissononce/cipher/
  • dissononce/hash/
• experimental: recognized by Noise community, not officially covered in Noise spec or endorsed by it, found under:
  • dissononce/extras/dh/experimental/
  • dissononce/extras/cipher/experimental/
  • dissononce/extras/hash/experimental/
• dangerous: a monkey might have written those, just don't use:
  • dissononce/extras/dh/dangerous/
  • dissononce/extras/cipher/dangerous/
  • dissononce/extras/hash/dangerous/

See Appendices for available Crypto functions.

Processing

HandshakeState, SymmetricState and CipherState should ideally be constructed in a composition-manner, where Crypto-functions dependencies are also to be instantiated before passing them to their dependants.

• A CipherState requires a Cipher object
• A SymmetricState requires a CipherState and a Hash object.
• A HandshakeState requires a SymmetricState and a DH object.

from dissononce.processing.impl.handshakestate import HandshakeState
from dissononce.processing.impl.symmetricstate import SymmetricState
from dissononce.processing.impl.cipherstate import CipherState
from dissononce.cipher.chachapoly import ChaChaPolyCipher
from dissononce.dh.x448.x448 import X448DH
from dissononce.hash.sha512 import SHA512Hash


handshakestate = HandshakeState(
    SymmetricState(
        CipherState(
            ChaChaPolyCipher()
        ),
        SHA512Hash()
    ),
    X448DH()
)

See Extras for alternative methods of construction.

Handshake Patterns

The HandshakePattern class allows authoring of patterns using a simple syntax, similar to how patterns are described in Noise spec.

• message_patterns is a tuple/list of tuples of token(s).
• initiator_pre_messages is a tuple of tokens
• responder_pre_message_pattern is a tuple of tokens

from dissononce.processing.handshakepatterns.handshakepattern import HandshakePattern

k1k1 = HandshakePattern(
      name='K1K1',
      initiator_pre_messages=('s',),
      responder_pre_message_pattern=('s',),
      message_patterns=(
          ('e',),
          ('e', 'ee', 'es'),
          ('se',)
    )
)

print(k1k1)

K1K1:
  -> s
  <- s
  ...
  -> e
  <- e, ee, es
  -> se

See Appendices for already defined Handshake Patterns.

Modifiers

A Modifier accepts a HandshakePattern and creates a new one with a modified name, and a modified set of message and premessage patterns

Fallback

from dissononce.processing.modifiers.fallback import FallbackPatternModifier
from dissononce.processing.handshakepatterns.interactive.XX import XXHandshakePattern


xx = XXHandshakePattern()
xx_fallback = FallbackPatternModifier().modify(xx)
print(xx_fallback)

XXfallback:
  -> e
  ...
  <- e, ee, s, es
  -> s, se

PSK

from dissononce.processing.modifiers.psk import PSKPatternModifier
from dissononce.processing.handshakepatterns.interactive.NN import NNHandshakePattern


nn = NNHandshakePattern()
nn_psk0 = PSKPatternModifier(0).modify(nn)
nn_psk02 = PSKPatternModifier(2).modify(nn_psk0)
print(nn_psk02)

NNpsk0+psk2:
  -> psk, e
  <- e, ee, psk

As usual, the modified HandshakePattern is used to (re)initialize a HandshakeState:

handshakestate.initialize(
    handshake_pattern=nn_psk02,
    initiator=True,
    prologue=b'',
    psks=(psk0, psk2)
)

Extras

Classes and functions that are not part of Noise Protocol specification but are part of this implementation are referred to as "Extras" or "Deviations". Examples for Extras are helpers, classes that simplify usage of the library, wrappers that enforce some rules or design patterns, or crypto functions that are not part of Noise Spec. Extras should be decoupled as much as possible from the base spec implementation and never referenced from there.

meta: Crypto-functions by name:

As an alternative to directly instantiating the Crypto-functions objects, they could also be created by name using a factory designated to each type of Crypto-functions:

from dissononce.extras.meta.hash.factory import HashFactory
from dissononce.extras.meta.dh.factory import DHFactory
from dissononce.extras.meta.cipher.factory import CipherFactory


cipher = CipherFactory().get_cipher('AESGCM')
hash = HashFactory().get_hash('SHA256')
dh = DHFactory().get_dh('25519')

Note that creating by name supports stable/official algorithms only at the moment.

meta: Protocol by name:

A Noise Protocol, that is:

• DH, Cipher, Hash instance
• CipherState instance
• SymmetricState instance
• HandshakeState instance
• HandshakePattern

can be created by name. Use NoiseProtocolFactory to get a a NoiseProtocol instance which encloses instances of DH, Cipher, Hash, HandshakePattern, and exposes methods for creating CipherState, SymmetricState, and HandshakeState.

from dissononce.extras.meta.protocol.factory import NoiseProtocolFactory

protocol = NoiseProtocolFactory().get_noise_protocol('Noise_XX_25519_AESGCM_SHA256')
handshakestate = protocol.create_handshakestate()

Note that creating by name supports stable/official algorithms only at the moment.

processing: GuardedHandshakeState

from dissononce.extras.processing.handshakestate_guarded import GuardedHandshakeState

guarded = GuardedHandshakeState(handshakestate)
guarded.read_message(b'', bytearray())

> AssertionError: Cannot read_message while in initialize phase.

GuardedHandshakeState wraps an existing HandshakeState to enforce a correct flow of the handshake process. This includes making sure the HandshakeState is initialized before usage, and that the flow order of write_message and read_message invocations match the HandshakePattern being used. A violation will result in an AssertionError getting raised.

processing: SwitchableHandshakeState

from dissononce.extras.processing.handshakestate_switchable import SwitchableHandshakeState
from dissononce.processing.handshakepatterns.interactive.XX import XXHandshakePattern
from dissononce.processing.modifiers.fallback import FallbackPatternModifier
from dissononce.extras.meta.protocol.factory import NoiseProtocolFactory

protocol = NoiseProtocolFactory().get_noise_protocol('Noise_IK_25519_AESGCM_SHA256')
switchable = SwitchableHandshakeState(protocol.create_handshakestate())

## Begin IK, then fallback to XX if necessary using:

switchable.switch(
    handshake_pattern=FallbackPatternModifier().modify(XXHandshakePattern()),
    initiator=True,
    prologue=b''
)

SwitchableHandshakeState facilitates transforming an ongoing Handshake into using a different pattern. Given the newHandshakePattern, it analyses the required initiator and responder pre-messages, and maintains them across the transformation for use in the new Handshake. This is typically used for example when doing a IK handshake then switching to XXfallback where re is to be used as a initiator pre-message.

Examples

Inside examples directory there are examples for some Noise protocols carrying out a handshake and transporting some messages for demonstration.

Testing

Test Vectors

Vectors used for testing are found under test/vectors. The data is of JSON type, and is formatted according to Noise Test Vectors Specification. At the moment there are 2 Test Vectors files:

• Tests Vectors from cacophony under tests/vectors/cacophony.txt
• Test Vectors from snow under tests/vectors/snow.txt

Logging

Enable debug-level logging for a detailed insight of a handshake process. The debug output syntax and formatting is intended to be as close as possible to the language used in Noise specs. This might be useful for when using dissononce as a reference implementation where one wants to understand what's going on internally and to easily relate to Noise specs.

>>> import dissononce, logging
>>> dissononce.logger.setLevel(logging.DEBUG)
>>> handshakestate.initialize(XXHandshakePattern(), True, b'', X448DH().generate_keypair())

I dissononce.processing.impl.handshakestate - Derived Noise Protocol name Noise_XX_448_ChaChaPoly_SHA512
XX:
  -> e
  <- e, ee, s, es
  -> s, se

>>> handshakestate.write_message(b'',bytearray())

I dissononce.processing.impl.handshakestate - WriteMessage(payload, message_buffer)
D dissononce.processing.impl.handshakestate -     Processing token 'e'
D dissononce.processing.impl.handshakestate -         e=GENERATE_KEYPAIR()
D dissononce.processing.impl.handshakestate -         message_buffer.append(e.public_key)
D dissononce.processing.impl.handshakestate -         MixHash(e.public_key)
D dissononce.processing.impl.handshakestate -     buffer.append(EncryptAndHash(payload))

Appendices

Cipher functions

Stable:

• AESGCM
• ChaChaPoly

Hash functions

Stable:

• Blake2b
• Blake2s
• SHA256
• SHA512

DH functions

Stable:

• x448
• x25519

Handshake Patterns

Interactive:

• IK, IN, IX
• KK, KN, KX
• NK, NN, NX
• XK, XN, XX

Oneway:

• K, N, X

Deferred:

• I1K, I1K1, I1N, I1X, I1X1, IK1, IX1
• K1K, K1K1, K1N, K1X, K1X1, KK1, KX1
• NK1, NX1
• X1K, X1K1, X1N, X1X, X1X1, XK1, XX1

Modifiers

• fallback
• psk

References

• noise specs revision 34
• noise mailing list
• noiseprotocol for python3
• noise-java