bookwyrm/bookwyrm/signatures.py
2021-03-08 08:49:10 -08:00

124 lines
4.2 KiB
Python

""" signs activitypub activities """
import hashlib
from urllib.parse import urlparse
import datetime
from base64 import b64encode, b64decode
from Crypto import Random
from Crypto.PublicKey import RSA
from Crypto.Signature import pkcs1_15 # pylint: disable=no-name-in-module
from Crypto.Hash import SHA256
MAX_SIGNATURE_AGE = 300
def create_key_pair():
""" a new public/private key pair, used for creating new users """
random_generator = Random.new().read
key = RSA.generate(1024, random_generator)
private_key = key.export_key().decode("utf8")
public_key = key.publickey().export_key().decode("utf8")
return private_key, public_key
def make_signature(sender, destination, date, digest):
""" uses a private key to sign an outgoing message """
inbox_parts = urlparse(destination)
signature_headers = [
"(request-target): post %s" % inbox_parts.path,
"host: %s" % inbox_parts.netloc,
"date: %s" % date,
"digest: %s" % digest,
]
message_to_sign = "\n".join(signature_headers)
signer = pkcs1_15.new(RSA.import_key(sender.key_pair.private_key))
signed_message = signer.sign(SHA256.new(message_to_sign.encode("utf8")))
signature = {
"keyId": "%s#main-key" % sender.remote_id,
"algorithm": "rsa-sha256",
"headers": "(request-target) host date digest",
"signature": b64encode(signed_message).decode("utf8"),
}
return ",".join('%s="%s"' % (k, v) for (k, v) in signature.items())
def make_digest(data):
""" creates a message digest for signing """
return "SHA-256=" + b64encode(hashlib.sha256(data.encode("utf-8")).digest()).decode(
"utf-8"
)
def verify_digest(request):
""" checks if a digest is syntactically valid and matches the message """
algorithm, digest = request.headers["digest"].split("=", 1)
if algorithm == "SHA-256":
hash_function = hashlib.sha256
elif algorithm == "SHA-512":
hash_function = hashlib.sha512
else:
raise ValueError("Unsupported hash function: {}".format(algorithm))
expected = hash_function(request.body).digest()
if b64decode(digest) != expected:
raise ValueError("Invalid HTTP Digest header")
class Signature:
""" read and validate incoming signatures """
def __init__(self, key_id, headers, signature):
self.key_id = key_id
self.headers = headers
self.signature = signature
@classmethod
def parse(cls, request):
""" extract and parse a signature from an http request """
signature_dict = {}
for pair in request.headers["Signature"].split(","):
k, v = pair.split("=", 1)
v = v.replace('"', "")
signature_dict[k] = v
try:
key_id = signature_dict["keyId"]
headers = signature_dict["headers"]
signature = b64decode(signature_dict["signature"])
except KeyError:
raise ValueError("Invalid auth header")
return cls(key_id, headers, signature)
def verify(self, public_key, request):
""" verify rsa signature """
if http_date_age(request.headers["date"]) > MAX_SIGNATURE_AGE:
raise ValueError("Request too old: %s" % (request.headers["date"],))
public_key = RSA.import_key(public_key)
comparison_string = []
for signed_header_name in self.headers.split(" "):
if signed_header_name == "(request-target)":
comparison_string.append("(request-target): post %s" % request.path)
else:
if signed_header_name == "digest":
verify_digest(request)
comparison_string.append(
"%s: %s" % (signed_header_name, request.headers[signed_header_name])
)
comparison_string = "\n".join(comparison_string)
signer = pkcs1_15.new(public_key)
digest = SHA256.new()
digest.update(comparison_string.encode())
# raises a ValueError if it fails
signer.verify(digest, self.signature)
def http_date_age(datestr):
""" age of a signature in seconds """
parsed = datetime.datetime.strptime(datestr, "%a, %d %b %Y %H:%M:%S GMT")
delta = datetime.datetime.utcnow() - parsed
return delta.total_seconds()