takahe/core/signatures.py
2022-12-20 13:21:50 +00:00

345 lines
12 KiB
Python

import base64
import json
from typing import Literal, TypedDict
from urllib.parse import urlparse
import httpx
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import padding, rsa
from django.conf import settings
from django.http import HttpRequest
from django.utils import timezone
from django.utils.http import http_date, parse_http_date
from httpx._types import TimeoutTypes
from pyld import jsonld
from core.ld import format_ld_date
class VerificationError(BaseException):
"""
There was an error with verifying the signature
"""
pass
class VerificationFormatError(VerificationError):
"""
There was an error with the format of the signature (not if it is valid)
"""
pass
class RsaKeys:
@classmethod
def generate_keypair(cls) -> tuple[str, str]:
"""
Generates a new RSA keypair
"""
private_key = rsa.generate_private_key(
public_exponent=65537,
key_size=2048,
)
private_key_serialized = private_key.private_bytes(
encoding=serialization.Encoding.PEM,
format=serialization.PrivateFormat.PKCS8,
encryption_algorithm=serialization.NoEncryption(),
).decode("ascii")
public_key_serialized = (
private_key.public_key()
.public_bytes(
encoding=serialization.Encoding.PEM,
format=serialization.PublicFormat.SubjectPublicKeyInfo,
)
.decode("ascii")
)
return private_key_serialized, public_key_serialized
class HttpSignature:
"""
Allows for calculation and verification of HTTP signatures
"""
@classmethod
def calculate_digest(cls, data, algorithm="sha-256") -> str:
"""
Calculates the digest header value for a given HTTP body
"""
if algorithm == "sha-256":
digest = hashes.Hash(hashes.SHA256())
digest.update(data)
return "SHA-256=" + base64.b64encode(digest.finalize()).decode("ascii")
else:
raise ValueError(f"Unknown digest algorithm {algorithm}")
@classmethod
def headers_from_request(cls, request: HttpRequest, header_names: list[str]) -> str:
"""
Creates the to-be-signed header payload from a Django request
"""
headers = {}
for header_name in header_names:
if header_name == "(request-target)":
value = f"{request.method.lower()} {request.path}"
elif header_name == "content-type":
value = request.META["CONTENT_TYPE"]
elif header_name == "content-length":
value = request.META["CONTENT_LENGTH"]
else:
value = request.META["HTTP_%s" % header_name.upper().replace("-", "_")]
headers[header_name] = value
return "\n".join(f"{name.lower()}: {value}" for name, value in headers.items())
@classmethod
def parse_signature(cls, signature: str) -> "HttpSignatureDetails":
bits = {}
for item in signature.split(","):
name, value = item.split("=", 1)
value = value.strip('"')
bits[name.lower()] = value
signature_details: HttpSignatureDetails = {
"headers": bits["headers"].split(),
"signature": base64.b64decode(bits["signature"]),
"algorithm": bits["algorithm"],
"keyid": bits["keyid"],
}
return signature_details
@classmethod
def compile_signature(cls, details: "HttpSignatureDetails") -> str:
value = f'keyId="{details["keyid"]}",headers="'
value += " ".join(h.lower() for h in details["headers"])
value += '",signature="'
value += base64.b64encode(details["signature"]).decode("ascii")
value += f'",algorithm="{details["algorithm"]}"'
return value
@classmethod
def verify_signature(
cls,
signature: bytes,
cleartext: str,
public_key: str,
):
public_key_instance = serialization.load_pem_public_key(
public_key.encode("ascii")
)
try:
public_key_instance.verify(
signature,
cleartext.encode("ascii"),
padding.PKCS1v15(),
hashes.SHA256(),
)
except InvalidSignature:
raise VerificationError("Signature mismatch")
@classmethod
def verify_request(cls, request, public_key, skip_date=False):
"""
Verifies that the request has a valid signature for its body
"""
# Verify body digest
if "digest" in request.headers:
expected_digest = HttpSignature.calculate_digest(request.body)
if request.headers["digest"] != expected_digest:
raise VerificationFormatError("Digest is incorrect")
# Verify date header
if "date" in request.headers and not skip_date:
header_date = parse_http_date(request.headers["date"])
if abs(timezone.now().timestamp() - header_date) > 60:
raise VerificationFormatError("Date is too far away")
# Get the signature details
if "signature" not in request.headers:
raise VerificationFormatError("No signature header present")
signature_details = cls.parse_signature(request.headers["signature"])
# Reject unknown algorithms
if signature_details["algorithm"] != "rsa-sha256":
raise VerificationFormatError("Unknown signature algorithm")
# Create the signature payload
headers_string = cls.headers_from_request(request, signature_details["headers"])
cls.verify_signature(
signature_details["signature"],
headers_string,
public_key,
)
@classmethod
async def signed_request(
cls,
uri: str,
body: dict | None,
private_key: str,
key_id: str,
content_type: str = "application/json",
method: Literal["get", "post"] = "post",
timeout: TimeoutTypes = settings.SETUP.REMOTE_TIMEOUT,
):
"""
Performs an async request to the given path, with a document, signed
as an identity.
"""
if "://" not in uri:
raise ValueError("URI does not contain a scheme")
# Create the core header field set
uri_parts = urlparse(uri)
date_string = http_date()
headers = {
"(request-target)": f"{method} {uri_parts.path}",
"Host": uri_parts.hostname,
"Date": date_string,
}
# If we have a body, add a digest and content type
if body is not None:
body_bytes = json.dumps(body).encode("utf8")
headers["Digest"] = cls.calculate_digest(body_bytes)
headers["Content-Type"] = content_type
else:
body_bytes = b""
# GET requests get implicit accept headers added
if method == "get":
headers["Accept"] = "application/ld+json"
# Sign the headers
signed_string = "\n".join(
f"{name.lower()}: {value}" for name, value in headers.items()
)
private_key_instance = serialization.load_pem_private_key(
private_key.encode("ascii"),
password=None,
)
signature = private_key_instance.sign(
signed_string.encode("ascii"),
padding.PKCS1v15(),
hashes.SHA256(),
)
headers["Signature"] = cls.compile_signature(
{
"keyid": key_id,
"headers": list(headers.keys()),
"signature": signature,
"algorithm": "rsa-sha256",
}
)
# Announce ourselves with an agent similar to Mastodon
headers["User-Agent"] = settings.TAKAHE_USER_AGENT
# Send the request with all those headers except the pseudo one
del headers["(request-target)"]
async with httpx.AsyncClient(timeout=timeout) as client:
response = await client.request(
method,
uri,
headers=headers,
content=body_bytes,
follow_redirects=method == "get",
)
if (
method == "post"
and response.status_code >= 400
and response.status_code < 500
and response.status_code != 404
):
raise ValueError(
f"POST error: {response.status_code} {response.content}"
)
return response
class HttpSignatureDetails(TypedDict):
algorithm: str
headers: list[str]
signature: bytes
keyid: str
class LDSignature:
"""
Creates and verifies signatures of JSON-LD documents
"""
@classmethod
def verify_signature(cls, document: dict, public_key: str) -> None:
"""
Verifies a document
"""
try:
# Strip out the signature from the incoming document
signature = document.pop("signature")
# Create the options document
options = {
"@context": "https://w3id.org/identity/v1",
"creator": signature["creator"],
"created": signature["created"],
}
except KeyError:
raise VerificationFormatError("Invalid signature section")
if signature["type"].lower() != "rsasignature2017":
raise VerificationFormatError("Unknown signature type")
# Get the normalised hash of each document
final_hash = cls.normalized_hash(options) + cls.normalized_hash(document)
# Verify the signature
public_key_instance = serialization.load_pem_public_key(
public_key.encode("ascii")
)
try:
public_key_instance.verify(
base64.b64decode(signature["signatureValue"]),
final_hash,
padding.PKCS1v15(),
hashes.SHA256(),
)
except InvalidSignature:
raise VerificationError("Signature mismatch")
@classmethod
def create_signature(
cls, document: dict, private_key: str, key_id: str
) -> dict[str, str]:
"""
Creates the signature for a document
"""
# Create the options document
options: dict[str, str] = {
"@context": "https://w3id.org/identity/v1",
"creator": key_id,
"created": format_ld_date(timezone.now()),
}
# Get the normalised hash of each document
final_hash = cls.normalized_hash(options) + cls.normalized_hash(document)
# Create the signature
private_key_instance = serialization.load_pem_private_key(
private_key.encode("ascii"),
password=None,
)
signature = base64.b64encode(
private_key_instance.sign(
final_hash,
padding.PKCS1v15(),
hashes.SHA256(),
)
)
# Add it to the options document along with other bits
options["signatureValue"] = signature.decode("ascii")
options["type"] = "RsaSignature2017"
return options
@classmethod
def normalized_hash(cls, document) -> bytes:
"""
Takes a JSON-LD document and create a hash of its URDNA2015 form,
in the same way that Mastodon does internally.
Reference: https://socialhub.activitypub.rocks/t/making-sense-of-rsasignature2017/347
"""
norm_form = jsonld.normalize(
document,
{"algorithm": "URDNA2015", "format": "application/n-quads"},
)
digest = hashes.Hash(hashes.SHA256())
digest.update(norm_form.encode("utf8"))
return digest.finalize().hex().encode("ascii")