fix: use secrets module to generate random bytes

Author: lepture

README.md

@@ -7,10 +7,9 @@
 
 `joserfc` is a Python library that provides a comprehensive implementation of several essential JSON Object Signing and Encryption (JOSE) standards.
 
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src/joserfc/rfc7516/models.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
-import os
 import typing as t
+import secrets
 from abc import ABCMeta, abstractmethod
 from ..registry import Header, HeaderRegistryDict
 from ..errors import InvalidKeyTypeError, InvalidKeyLengthError
@@ -168,10 +168,10 @@ class JWEEncModel(object, metaclass=ABCMeta):
     cek_size: int
 
     def generate_cek(self) -> bytes:
-        return os.urandom(self.cek_size // 8)
+        return secrets.token_bytes(self.cek_size // 8)
 
     def generate_iv(self) -> bytes:
-        return os.urandom(self.iv_size // 8)
+        return secrets.token_bytes(self.iv_size // 8)
 
     def check_iv(self, iv: bytes) -> bytes:
         if len(iv) * 8 != self.iv_size:  # pragma: no cover

src/joserfc/rfc7518/jwe_algs.py

@@ -1,5 +1,5 @@
 from __future__ import annotations
-from os import urandom
+import secrets
 from cryptography.hazmat.primitives.asymmetric import padding
 from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.backends import default_backend
@@ -151,7 +151,7 @@ def encrypt_cek(self, cek: bytes, recipient: Recipient[OctKey]) -> bytes:
         #: The "iv" (initialization vector) Header Parameter value is the
         #: base64url-encoded representation of the 96-bit IV value
         iv_size = 96
-        iv = urandom(iv_size // 8)
+        iv = secrets.token_bytes(iv_size // 8)
 
         cipher = Cipher(AES(op_key), GCM(iv), backend=default_backend())
         enc = cipher.encryptor()
@@ -264,7 +264,7 @@ def compute_derived_key(self, key: bytes, p2s: bytes, p2c: int) -> bytes:
     def encrypt_cek(self, cek: bytes, recipient: Recipient[OctKey]) -> bytes:
         headers = recipient.headers()
         if "p2s" not in headers:
-            p2s = urandom(16)
+            p2s = secrets.token_bytes(16)
             recipient.add_header("p2s", urlsafe_b64encode(p2s).decode("ascii"))
         else:
             p2s = urlsafe_b64decode(to_bytes(headers["p2s"]))

src/joserfc/rfc7518/oct_key.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 from typing import Any
-from os import urandom
+import secrets
 from ..util import (
     to_bytes,
     urlsafe_b64decode,
@@ -68,8 +68,7 @@ def generate_key(
         if key_size % 8 != 0:
             raise ValueError("Invalid bit size for oct key")
 
-        value = urandom(key_size // 8)
-        raw_key = to_bytes(value)
+        raw_key = secrets.token_bytes(key_size // 8)
         key: OctKey = cls(raw_key, raw_key, parameters)
         if auto_kid:
             key.ensure_kid()