import base64 import json from typing import Dict, List, Literal, TypedDict from urllib.parse import urlparse import httpx from cryptography.hazmat.primitives import hashes from django.http import HttpRequest from django.utils import timezone from django.utils.http import http_date, parse_http_date from OpenSSL import crypto 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 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"post {request.path}" elif header_name == "content-type": value = request.META["CONTENT_TYPE"] 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, ): x509 = crypto.X509() x509.set_pubkey( crypto.load_publickey( crypto.FILETYPE_PEM, public_key.encode("ascii"), ) ) try: crypto.verify(x509, signature, cleartext.encode("ascii"), "sha256") except crypto.Error: 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 "HTTP_DIGEST" in request.META: expected_digest = HttpSignature.calculate_digest(request.body) if request.META["HTTP_DIGEST"] != expected_digest: raise VerificationFormatError("Digest is incorrect") # Verify date header if "HTTP_DATE" in request.META and not skip_date: header_date = parse_http_date(request.META["HTTP_DATE"]) if abs(timezone.now().timestamp() - header_date) > 60: raise VerificationFormatError("Date is too far away") # Get the signature details if "HTTP_SIGNATURE" not in request.META: raise VerificationFormatError("No signature header present") signature_details = cls.parse_signature(request.META["HTTP_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( self, uri: str, body: Dict, private_key: str, key_id: str, content_type: str = "application/json", method: Literal["post"] = "post", ): """ Performs an async request to the given path, with a document, signed as an identity. """ uri_parts = urlparse(uri) date_string = http_date() body_bytes = json.dumps(body).encode("utf8") headers = { "(request-target)": f"{method} {uri_parts.path}", "Host": uri_parts.hostname, "Date": date_string, "Digest": self.calculate_digest(body_bytes), "Content-Type": content_type, } signed_string = "\n".join( f"{name.lower()}: {value}" for name, value in headers.items() ) pkey = crypto.load_privatekey( crypto.FILETYPE_PEM, private_key.encode("ascii"), ) signature = crypto.sign( pkey, signed_string.encode("ascii"), "sha256", ) headers["Signature"] = self.compile_signature( { "keyid": key_id, "headers": list(headers.keys()), "signature": signature, "algorithm": "rsa-sha256", } ) del headers["(request-target)"] async with httpx.AsyncClient() as client: response = await client.request( method, uri, headers=headers, content=body_bytes, ) if response.status_code >= 400: raise ValueError( f"Request 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 x509 = crypto.X509() x509.set_pubkey( crypto.load_publickey( crypto.FILETYPE_PEM, public_key.encode("ascii"), ) ) try: crypto.verify( x509, base64.b64decode(signature["signatureValue"]), final_hash, "sha256", ) except crypto.Error: 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 pkey = crypto.load_privatekey( crypto.FILETYPE_PEM, private_key.encode("ascii"), ) signature = base64.b64encode(crypto.sign(pkey, final_hash, "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")