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