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# Copyright (c) 2024 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 PRF extension,
creates a new credential for it with the extension enabled, and uses it to
derive two separate secrets.
"""
from fido2.server import Fido2Server
from fido2.utils import websafe_encode
from exampleutils import get_client
import sys
import os
# Locate a suitable FIDO authenticator
client = get_client(lambda client: "hmac-secret" in client.info.extensions)
uv = "discouraged"
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": {"prf": {}},
}
)
# Complete registration
auth_data = server.register_complete(
state, result.client_data, result.attestation_object
)
credential = auth_data.credential_data
# PRF result:
if not result.extension_results.get("prf", {}).get("enabled"):
print("Failed to create credential with PRF", result.extension_results)
sys.exit(1)
print("New credential created, with the PRF extension.")
# If created with UV, keep using UV
if result.attestation_object.auth_data.is_user_verified():
uv = "required"
# Generate a salt for PRF:
salt = websafe_encode(os.urandom(32))
print("Authenticate with salt:", salt)
# Prepare parameters for getAssertion
credentials = [credential]
request_options, state = server.authenticate_begin(credentials, user_verification=uv)
# Authenticate the credential
result = client.get_assertion(
{
**request_options["publicKey"],
"extensions": {"prf": {"eval": {"first": salt}}},
}
)
# Only one cred in allowCredentials, only one response.
response = result.get_response(0)
output1 = response.extension_results["prf"]["results"]["first"]
print("Authenticated, secret:", output1)
# Authenticate again, using two salts to generate two secrets.
# This time we will use evalByCredential, which can be used if there are multiple
# credentials which use different salts. Here it is not needed, but provided for
# completeness of the example.
# Generate a second salt for PRF:
salt2 = websafe_encode(os.urandom(32))
print("Authenticate with second salt:", salt2)
# The first salt is reused, which should result in the same secret.
result = client.get_assertion(
{
**request_options["publicKey"],
"extensions": {
"prf": {
"evalByCredential": {
websafe_encode(credential.credential_id): {
"first": salt,
"second": salt2,
}
}
}
},
}
)
# Only one cred in allowCredentials, only one response.
response = result.get_response(0)
output = response.extension_results["prf"]["results"]
print("Old secret:", output["first"])
print("New secret:", output["second"])
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