An implementation of the SCRAM protocol.
Project description
Scramp
A Python implementation of the SCRAM authentication protocol. Scramp supports the following mechanisms:
- SCRAM-SHA-1
- SCRAM-SHA-1-PLUS
- SCRAM-SHA-256
- SCRAM-SHA-256-PLUS
- SCRAM-SHA-512
- SCRAM-SHA-512-PLUS
- SCRAM-SHA3-512
- SCRAM-SHA3-512-PLUS
Installation
- Create a virtual environment:
python3 -m venv venv
- Activate the virtual environment:
source venv/bin/activate
- Install:
pip install scramp
Examples
Client and Server
Here's an example using both the client and the server. It's a bit contrived as normally you'd be using either the client or server on its own.
>>> from scramp import ScramClient, ScramMechanism
>>>
>>> USERNAME = 'user'
>>> PASSWORD = 'pencil'
>>> MECHANISMS = ['SCRAM-SHA-256']
>>>
>>>
>>> # Choose a mechanism for our server
>>> m = ScramMechanism() # Default is SCRAM-SHA-256
>>>
>>> # On the server side we create the authentication information for each user
>>> # and store it in an authentication database. We'll use a dict:
>>> db = {}
>>>
>>> salt, stored_key, server_key, iteration_count = m.make_auth_info(PASSWORD)
>>>
>>> db[USERNAME] = salt, stored_key, server_key, iteration_count
>>>
>>> # Define your own function for retrieving the authentication information
>>> # from the database given a username
>>>
>>> def auth_fn(username):
... return db[username]
>>>
>>> # Make the SCRAM server
>>> s = m.make_server(auth_fn)
>>>
>>> # Now set up the client and carry out authentication with the server
>>> c = ScramClient(MECHANISMS, USERNAME, PASSWORD)
>>> cfirst = c.get_client_first()
>>>
>>> s.set_client_first(cfirst)
>>> sfirst = s.get_server_first()
>>>
>>> c.set_server_first(sfirst)
>>> cfinal = c.get_client_final()
>>>
>>> s.set_client_final(cfinal)
>>> sfinal = s.get_server_final()
>>>
>>> c.set_server_final(sfinal)
>>>
>>> # If it all runs through without raising an exception, the authentication
>>> # has succeeded
Client only
Here's an example using just the client. The client nonce is specified in order to give
a reproducible example, but in production you'd omit the c_nonce
parameter and let
ScramClient
generate a client nonce:
>>> from scramp import ScramClient
>>>
>>> USERNAME = 'user'
>>> PASSWORD = 'pencil'
>>> C_NONCE = 'rOprNGfwEbeRWgbNEkqO'
>>> MECHANISMS = ['SCRAM-SHA-256']
>>>
>>> # Normally the c_nonce would be omitted, in which case ScramClient will
>>> # generate the nonce itself.
>>>
>>> c = ScramClient(MECHANISMS, USERNAME, PASSWORD, c_nonce=C_NONCE)
>>>
>>> # Get the client first message and send it to the server
>>> cfirst = c.get_client_first()
>>> print(cfirst)
n,,n=user,r=rOprNGfwEbeRWgbNEkqO
>>>
>>> # Set the first message from the server
>>> c.set_server_first(
... 'r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,'
... 's=W22ZaJ0SNY7soEsUEjb6gQ==,i=4096')
>>>
>>> # Get the client final message and send it to the server
>>> cfinal = c.get_client_final()
>>> print(cfinal)
c=biws,r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,p=dHzbZapWIk4jUhN+Ute9ytag9zjfMHgsqmmiz7AndVQ=
>>>
>>> # Set the final message from the server
>>> c.set_server_final('v=6rriTRBi23WpRR/wtup+mMhUZUn/dB5nLTJRsjl95G4=')
>>>
>>> # If it all runs through without raising an exception, the authentication
>>> # has succeeded
Server only
Here's an example using just the server. The server nonce and salt is specified in order
to give a reproducible example, but in production you'd omit the s_nonce
and salt
parameters and let Scramp generate them:
>>> from scramp import ScramMechanism
>>>
>>> USERNAME = 'user'
>>> PASSWORD = 'pencil'
>>> S_NONCE = '%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0'
>>> SALT = b'[m\x99h\x9d\x125\x8e\xec\xa0K\x14\x126\xfa\x81'
>>>
>>> db = {}
>>>
>>> m = ScramMechanism()
>>>
>>> salt, stored_key, server_key, iteration_count = m.make_auth_info(
... PASSWORD, salt=SALT)
>>>
>>> db[USERNAME] = salt, stored_key, server_key, iteration_count
>>>
>>> # Define your own function for getting a password given a username
>>> def auth_fn(username):
... return db[username]
>>>
>>> # Normally the s_nonce parameter would be omitted, in which case the
>>> # server will generate the nonce itself.
>>>
>>> s = m.make_server(auth_fn, s_nonce=S_NONCE)
>>>
>>> # Set the first message from the client
>>> s.set_client_first('n,,n=user,r=rOprNGfwEbeRWgbNEkqO')
>>>
>>> # Get the first server message, and send it to the client
>>> sfirst = s.get_server_first()
>>> print(sfirst)
r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,s=W22ZaJ0SNY7soEsUEjb6gQ==,i=4096
>>>
>>> # Set the final message from the client
>>> s.set_client_final(
... 'c=biws,r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,'
... 'p=dHzbZapWIk4jUhN+Ute9ytag9zjfMHgsqmmiz7AndVQ=')
>>>
>>> # Get the final server message and send it to the client
>>> sfinal = s.get_server_final()
>>> print(sfinal)
v=6rriTRBi23WpRR/wtup+mMhUZUn/dB5nLTJRsjl95G4=
>>>
>>> # If it all runs through without raising an exception, the authentication
>>> # has succeeded
Server only with passlib
Here's an example using just the server and using the passlib hashing library. The server nonce and salt is
specified in order to give a reproducible example, but in production you'd omit the
s_nonce
and salt
parameters and let Scramp generate them:
>>> from scramp import ScramMechanism
>>> from passlib.hash import scram
>>>
>>> USERNAME = 'user'
>>> PASSWORD = 'pencil'
>>> S_NONCE = '%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0'
>>> SALT = b'[m\x99h\x9d\x125\x8e\xec\xa0K\x14\x126\xfa\x81'
>>> ITERATION_COUNT = 4096
>>>
>>> db = {}
>>> hash = scram.using(salt=SALT, rounds=ITERATION_COUNT).hash(PASSWORD)
>>>
>>> salt, iteration_count, digest = scram.extract_digest_info(hash, 'sha-256')
>>>
>>> stored_key, server_key = m.make_stored_server_keys(digest)
>>>
>>> db[USERNAME] = salt, stored_key, server_key, iteration_count
>>>
>>> # Define your own function for getting a password given a username
>>> def auth_fn(username):
... return db[username]
>>>
>>> # Normally the s_nonce parameter would be omitted, in which case the
>>> # server will generate the nonce itself.
>>>
>>> m = ScramMechanism()
>>> s = m.make_server(auth_fn, s_nonce=S_NONCE)
>>>
>>> # Set the first message from the client
>>> s.set_client_first('n,,n=user,r=rOprNGfwEbeRWgbNEkqO')
>>>
>>> # Get the first server message, and send it to the client
>>> sfirst = s.get_server_first()
>>> print(sfirst)
r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,s=W22ZaJ0SNY7soEsUEjb6gQ==,i=4096
>>>
>>> # Set the final message from the client
>>> s.set_client_final(
... 'c=biws,r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,'
... 'p=dHzbZapWIk4jUhN+Ute9ytag9zjfMHgsqmmiz7AndVQ=')
>>>
>>> # Get the final server message and send it to the client
>>> sfinal = s.get_server_final()
>>> print(sfinal)
v=6rriTRBi23WpRR/wtup+mMhUZUn/dB5nLTJRsjl95G4=
>>>
>>> # If it all runs through without raising an exception, the authentication
>>> # has succeeded
Server Error
Here's an example of when setting a message from the client causes an error. The server
nonce and salt is specified in order to give a reproducible example, but in production
you'd omit the s_nonce
and salt
parameters and let Scramp generate them:
>>> from scramp import ScramException, ScramMechanism
>>>
>>> USERNAME = 'user'
>>> PASSWORD = 'pencil'
>>> S_NONCE = '%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0'
>>> SALT = b'[m\x99h\x9d\x125\x8e\xec\xa0K\x14\x126\xfa\x81'
>>>
>>> db = {}
>>>
>>> m = ScramMechanism()
>>>
>>> salt, stored_key, server_key, iteration_count = m.make_auth_info(
... PASSWORD, salt=SALT)
>>>
>>> db[USERNAME] = salt, stored_key, server_key, iteration_count
>>>
>>> # Define your own function for getting a password given a username
>>> def auth_fn(username):
... return db[username]
>>>
>>> # Normally the s_nonce parameter would be omitted, in which case the
>>> # server will generate the nonce itself.
>>>
>>> s = m.make_server(auth_fn, s_nonce=S_NONCE)
>>>
>>> try:
... # Set the first message from the client
... s.set_client_first('p=tls-unique,,n=user,r=rOprNGfwEbeRWgbNEkqO')
... except ScramException as e:
... print(e)
... # Get the final server message and send it to the client
... sfinal = s.get_server_final()
... print(sfinal)
Received GS2 flag 'p' which indicates that the client requires channel binding, but the server does not: channel-binding-not-supported
e=channel-binding-not-supported
Standards
- RFC 5802 Describes SCRAM.
- RFC 7677 Registers SCRAM-SHA-256 and SCRAM-SHA-256-PLUS.
- draft-melnikov-scram-sha-512-02 Registers SCRAM-SHA-512 and SCRAM-SHA-512-PLUS.
- draft-melnikov-scram-sha3-512 Registers SCRAM-SHA3-512 and SCRAM-SHA3-512-PLUS.
- RFC 5929 Channel Bindings for TLS.
- draft-ietf-kitten-tls-channel-bindings-for-tls13 Defines the
tls-exporter
channel binding, which is not yet supported by Scramp.
API Docs
scramp.MECHANISMS
A tuple of the supported mechanism names.
scramp.ScramClient
ScramClient(mechanisms, username, password, channel_binding=None, c_nonce=None)
Constructor of the scramp.ScramClient
class, with the following parameters:
mechanisms
- A list or tuple of mechanism names. ScramClient will choose the most secure. Ifcbind_data
isNone
, the '-PLUS' variants will be filtered out first. The chosen mechanism is available as the propertymechanism_name
.username
password
channel_binding
- Providing a value for this parameter allows channel binding to be used (ie. it lets you use mechanisms ending in '-PLUS'). The value forchannel_binding
is a tuple consisting of the channel binding name and the channel binding data. For example, if the channel binding name istls-unique
, thechannel_binding
parameter would be('tls-unique', data)
, wheredata
is obtained by calling SSLSocket.get_channel_binding(). The convenience functionscramp.make_channel_binding()
can be used to create a channel binding tuple.c_nonce
- The client nonce. It's sometimes useful to set this when testing / debugging, but in production this should be omitted, in which caseScramClient
will generate a client nonce.
The ScramClient
object has the following methods and properties:
get_client_first()
- Get the client first message.set_server_first(message)
- Set the first message from the server.get_client_final()
- Get the final client message.set_server_final(message)
- Set the final message from the server.mechanism_name
- The mechanism chosen from the list given in the constructor.
scramp.ScramMechanism
ScramMechanism(mechanism='SCRAM-SHA-256')
Constructor of the ScramMechanism
class, with the following parameter:
mechanism
- The SCRAM mechanism to use.
The ScramMechanism
object has the following methods and properties:
make_auth_info(password, iteration_count=None, salt=None)
- Returns the tuple(salt, stored_key, server_key, iteration_count)
which is stored in the authentication database on the server side. It has the following parameters:password
- The user's password as astr
.iteration_count
- The rounds as anint
. IfNone
then use the minimum associated with the mechanism.salt
- It's sometimes useful to set this binary parameter when testing / debugging, but in production this should be omitted, in which case a salt will be generated.
make_server(auth_fn, channel_binding=None, s_nonce=None)
- returns aScramServer
object. It takes the following parameters:auth_fn
This is a function provided by the programmer that has one parameter, a username of typestr
and returns returns the tuple(salt, stored_key, server_key, iteration_count)
. Wheresalt
,stored_key
andserver_key
are of a binary type, anditeration_count
is anint
.channel_binding
- Providing a value for this parameter allows channel binding to be used (ie. it lets you use mechanisms ending in-PLUS
). The value forchannel_binding
is a tuple consisting of the channel binding name and the channel binding data. For example, if the channel binding name is 'tls-unique', thechannel_binding
parameter would be('tls-unique', data)
, wheredata
is obtained by calling SSLSocket.get_channel_binding(). The convenience functionscramp.make_channel_binding()
can be used to create a channel binding tuple. Ifchannel_binding
is provided and the mechanism isn't a-PLUS
variant, then the server will negotiate with the client to use the-PLUS
variant if the client supports it, or otherwise to use the mechanism without channel binding.s_nonce
- The server nonce as astr
. It's sometimes useful to set this when testing / debugging, but in production this should be omitted, in which caseScramServer
will generate a server nonce.
make_stored_server_keys(salted_password)
- Returns(stored_key, server_key)
tuple ofbytes
objects given a salted password. This is useful if you want to use a separate hashing implementation from the one provided by Scramp. It takes the following parameter:salted_password
- A binary object representing the hashed password.
iteration_count
- The minimum iteration count recommended for this mechanism.
scramp.ScramServer
The ScramServer
object has the following methods:
set_client_first(message)
- Set the first message from the client.get_server_first()
- Get the server first message.set_client_final(message)
- Set the final client message.get_server_final()
- Get the server final message.
scramp.make_channel_binding(name, ssl_socket)
A helper function that makes a channel_binding
tuple when given a channel binding name and an SSL socket. The parameters are:
name
- A channel binding name such as 'tls-unique' or 'tls-server-end-point'.ssl_socket
- An instance of ssl.SSLSocket.
Testing
- Activate the virtual environment:
source venv/bin/activate
- Install
tox
:pip install tox
- Run
tox
:tox
OpenSSF Scorecard
It might be worth running the OpenSSF Scorecard:
sudo docker run -e GITHUB_AUTH_TOKEN=<auth_token> gcr.io/openssf/scorecard:stable --repo=github.com/tlocke/scramp
Doing A Release Of Scramp
Run tox
to make sure all tests pass, then update the release notes, then do:
git tag -a x.y.z -m "version x.y.z"
rm -r dist
python -m build
twine upload dist/*
Release Notes
Version 1.4.5, 2024-04-13
- Drop support for Python 3.7, which means we're not dependent on
importlib-metadata
anymore. - Various changes to build system, docs and automated testing.
Version 1.4.4, 2022-11-01
- Tighten up parsing of messages to make sure that a
ScramException
is raised if a message is malformed.
Version 1.4.3, 2022-10-26
- The client now sends a gs2-cbind-flag of 'y' if the client supports channel binding, but thinks the server does not.
Version 1.4.2, 2022-10-22
- Switch to using the MIT-0 licence https://choosealicense.com/licenses/mit-0/
- When creating a ScramClient, allow non
-PLUS
variants, even if achannel_binding
parameter is provided. Previously this would raise and exception.
Version 1.4.1, 2021-08-25
- When using
make_channel_binding()
to create a tls-server-end-point channel binding, support certificates with hash algorithm of sha512.
Version 1.4.0, 2021-03-28
- Raise an exception if the client receives an error from the server.
Version 1.3.0, 2021-03-28
- As the specification allows, server errors are now sent to the client in the
server_final
message, an exception is still thrown as before.
Version 1.2.2, 2021-02-13
- Fix bug in generating the AuthMessage. It was incorrect when channel binding was used. So now Scramp supports channel binding.
Version 1.2.1, 2021-02-07
- Add support for channel binding.
- Add support for SCRAM-SHA-512 and SCRAM-SHA3-512 and their channel binding variants.
Version 1.2.0, 2020-05-30
- This is a backwardly incompatible change on the server side, the client side will work as before. The idea of this change is to make it possible to have an authentication database. That is, the authentication information can be stored, and then retrieved when needed to authenticate the user.
- In addition, it's now possible on the server side to use a third party hashing library such as passlib as the hashing implementation.
Version 1.1.1, 2020-03-28
- Add the README and LICENCE to the distribution.
Version 1.1.0, 2019-02-24
- Add support for the SCRAM-SHA-1 mechanism.
Version 1.0.0, 2019-02-17
- Implement the server side as well as the client side.
Version 0.0.0, 2019-02-10
Project details
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