import base64 import json from ssl import SSLCertVerificationError, SSLError from typing import Literal, TypedDict, cast 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 idna.core import InvalidCodepoint 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.headers["content-type"] elif header_name == "content-length": value = request.headers["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: rsa.RSAPublicKey = cast( rsa.RSAPublicKey, 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 # hs2019 is used by some libraries to obfuscate the real algorithm per the spec # https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures-12 if ( signature_details["algorithm"] != "rsa-sha256" and signature_details["algorithm"] != "hs2019" ): 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 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: rsa.RSAPrivateKey = cast( rsa.RSAPrivateKey, 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)"] with httpx.Client(timeout=timeout) as client: try: response = client.request( method, uri, headers=headers, content=body_bytes, follow_redirects=method == "get", ) except SSLError as invalid_cert: # Not our problem if the other end doesn't have proper SSL print(f"{uri} {invalid_cert}") raise SSLCertVerificationError(invalid_cert) from invalid_cert except InvalidCodepoint as ex: # Convert to a more generic error we handle raise httpx.HTTPError(f"InvalidCodepoint: {str(ex)}") from None if ( method == "post" and response.status_code >= 400 and response.status_code < 500 and response.status_code != 404 ): raise ValueError( f"POST error to {uri}: {response.status_code} {response.content!r}" ) 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: rsa.RSAPublicKey = cast( rsa.RSAPublicKey, 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: rsa.RSAPrivateKey = cast( rsa.RSAPrivateKey, 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")