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# Copyright (c) 2018 Yubico AB
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or
# without modification, are permitted provided that the following
# conditions are met:
#
# 1. Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following
# disclaimer in the documentation and/or other materials provided
# with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
"""
Connects to the first FIDO device found which supports the HmacSecret extension,
creates a new credential for it with the extension enabled, and uses it to
derive two separate secrets.
NOTE: This extension is not enabled by default as direct access to the extension
is now allowed in a browser setting. See also prf.py for an example which uses
the PRF extension which is enabled by default.
"""
import ctypes
import os
import sys
from exampleutils import CliInteraction, enumerate_devices
from fido2.client import DefaultClientDataCollector, Fido2Client
from fido2.ctap2.extensions import HmacSecretExtension
from fido2.server import Fido2Server
# Use the Windows WebAuthn API if available, and we're not running as admin
try:
from fido2.client.windows import WindowsClient
use_winclient = (
WindowsClient.is_available() and not ctypes.windll.shell32.IsUserAnAdmin()
)
except ImportError:
use_winclient = False
uv = "discouraged"
if use_winclient:
# Use the Windows WebAuthn API if available, and we're not running as admin
# By default only the PRF extension is allowed, we need to explicitly
# configure the client to allow hmac-secret
client = WindowsClient("https://example.com", allow_hmac_secret=True)
else:
# Locate a device
for dev in enumerate_devices():
client = Fido2Client(
dev,
client_data_collector=DefaultClientDataCollector("https://example.com"),
user_interaction=CliInteraction(),
# By default only the PRF extension is allowed, we need to explicitly
# configure the client to allow hmac-secret
extensions=[HmacSecretExtension(allow_hmac_secret=True)],
)
if "hmac-secret" in client.info.extensions:
break
else:
print("No Authenticator with the HmacSecret extension found!")
sys.exit(1)
server = Fido2Server({"id": "example.com", "name": "Example RP"}, attestation="none")
user = {"id": b"user_id", "name": "A. User"}
# Prepare parameters for makeCredential
create_options, state = server.register_begin(
user,
resident_key_requirement="discouraged",
user_verification=uv,
authenticator_attachment="cross-platform",
)
# Create a credential
result = client.make_credential(
{
**create_options["publicKey"],
"extensions": {"hmacCreateSecret": True},
}
)
# Complete registration
auth_data = server.register_complete(state, result)
credentials = [auth_data.credential_data]
# HmacSecret result:
if result.client_extension_results.get("hmacCreateSecret"):
print("New credential created, with HmacSecret")
else:
# This fails on Windows, but we might still be able to use hmac-secret even if
# the credential wasn't made with it, so keep going
print("Failed to create credential with HmacSecret, it might not work")
# Generate a salt for HmacSecret:
salt = os.urandom(32)
print("Authenticate with salt:", salt.hex())
# Prepare parameters for getAssertion
request_options, state = server.authenticate_begin(credentials, user_verification=uv)
# Authenticate the credential
result = client.get_assertion(
{
**request_options["publicKey"],
"extensions": {"hmacGetSecret": {"salt1": salt}},
}
)
# Only one cred in allowCredentials, only one response.
result = result.get_response(0)
output1 = result.client_extension_results.hmac_get_secret.output1
print("Authenticated, secret:", output1.hex())
# Authenticate again, using two salts to generate two secrets:
# Generate a second salt for HmacSecret:
salt2 = os.urandom(32)
print("Authenticate with second salt:", salt2.hex())
# The first salt is reused, which should result in the same secret.
result = client.get_assertion(
{
**request_options["publicKey"],
"extensions": {"hmacGetSecret": {"salt1": salt, "salt2": salt2}},
}
)
# Only one cred in allowCredentials, only one response.
result = result.get_response(0)
output = result.client_extension_results.hmac_get_secret
print("Old secret:", output.output1.hex())
print("New secret:", output.output2.hex())
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