cred_blob.py

# Copyright (c) 2020 Yubico AB
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"""
Connects to the first FIDO device found which supports the CredBlob extension,
creates a new credential for it with the extension enabled, and stores some data.
"""
from fido2.server import Fido2Server
from exampleutils import get_client
import sys
import os


# Locate a suitable FIDO authenticator
client = get_client(lambda client: "credBlob" in client.info.extensions)


# Prefer UV token if supported
uv = "discouraged"
if client.info.options.get("uv") or client.info.options.get("bioEnroll"):
    uv = "preferred"
    print("Authenticator is configured for User Verification")


server = Fido2Server({"id": "example.com", "name": "Example RP"})
user = {"id": b"user_id", "name": "A. User"}

# Prepare parameters for makeCredential
create_options, state = server.register_begin(
    user,
    resident_key_requirement="required",
    user_verification=uv,
    authenticator_attachment="cross-platform",
)

# Add CredBlob extension, attach data
blob = os.urandom(32)  # 32 random bytes

# Create a credential
result = client.make_credential(
    {
        **create_options["publicKey"],
        "extensions": {"credBlob": blob},
    }
)

# Complete registration
auth_data = server.register_complete(
    state, result.client_data, result.attestation_object
)
credentials = [auth_data.credential_data]


# CredBlob result:
if not auth_data.extensions.get("credBlob"):
    print("Credential was registered, but credBlob was NOT saved.")
    sys.exit(1)

print("New credential created, with the CredBlob extension.")

# Prepare parameters for getAssertion
request_options, state = server.authenticate_begin()

# Authenticate the credential
# Only one cred in allowCredentials, only one response.
result = client.get_assertion(
    {
        **request_options["publicKey"],
        "extensions": {"getCredBlob": True},
    }
).get_response(0)

blob_res = result.authenticator_data.extensions.get("credBlob")

if blob == blob_res:
    print("Authenticated, got correct blob:", blob.hex())
else:
    print(
        "Authenticated, got incorrect blob! (was %s, expected %s)"
        % (blob_res.hex(), blob.hex())
    )
    sys.exit(1)