Google App Engine + PyCrypto =/dev/urandom无法访问

Question

我正在使用Google App Engine和PyCrypto进行一些加密。我得到的错误如下，仅在我的本地开发服务器上运行Linux Mint Maya（13）时出现。我将相同的代码部署到GAE云，并且运行时没有错误。

ERROR 2012-06-29 16:04:20,717 webapp2.py:1553] [Errno 13] file not accessible: '/dev/urandom' 
Traceback (most recent call last): 
    File "/home/eric/google_appengine/lib/webapp2/webapp2.py", line 1536, in __call__ 
    rv = self.handle_exception(request, response, e) 
    File "/home/eric/google_appengine/lib/webapp2/webapp2.py", line 1530, in __call__ 
    rv = self.router.dispatch(request, response) 
    File "/home/eric/google_appengine/lib/webapp2/webapp2.py", line 1278, in default_dispatcher 
    return route.handler_adapter(request, response) 
    File "/home/eric/google_appengine/lib/webapp2/webapp2.py", line 1102, in __call__ 
    return handler.dispatch() 
    File "/home/eric/google_appengine/lib/webapp2/webapp2.py", line 572, in dispatch 
    return self.handle_exception(e, self.app.debug) 
    File "/home/eric/google_appengine/lib/webapp2/webapp2.py", line 570, in dispatch 
    return method(*args, **kwargs) 
    File "/home/eric/workspace/commentbox/src/controller/api.py", line 55, in get 
    self.response.out.write(encrypt(json.dumps(to_json))) 
    File "/home/eric/workspace/commentbox/src/controller/api.py", line 27, in encrypt 
    iv = Random.new().read(AES.block_size) 
    File "/usr/lib/python2.7/dist-packages/Crypto/Random/__init__.py", line 33, in new 
    return _UserFriendlyRNG.new(*args, **kwargs) 
    File "/usr/lib/python2.7/dist-packages/Crypto/Random/_UserFriendlyRNG.py", line 206, in new 
    return RNGFile(_get_singleton()) 
    File "/usr/lib/python2.7/dist-packages/Crypto/Random/_UserFriendlyRNG.py", line 200, in _get_singleton 
    _singleton = _LockingUserFriendlyRNG() 
    File "/usr/lib/python2.7/dist-packages/Crypto/Random/_UserFriendlyRNG.py", line 144, in __init__ 
    _UserFriendlyRNG.__init__(self) 
    File "/usr/lib/python2.7/dist-packages/Crypto/Random/_UserFriendlyRNG.py", line 86, in __init__ 
    self._ec = _EntropyCollector(self._fa) 
    File "/usr/lib/python2.7/dist-packages/Crypto/Random/_UserFriendlyRNG.py", line 53, in __init__ 
    self._osrng = OSRNG.new() 
    File "/usr/lib/python2.7/dist-packages/Crypto/Random/OSRNG/posix.py", line 60, in new 
    return DevURandomRNG(*args, **kwargs) 
    File "/usr/lib/python2.7/dist-packages/Crypto/Random/OSRNG/posix.py", line 42, in __init__ 
    f = open(self.name, "rb", 0) 
    File "/home/eric/google_appengine/google/appengine/tools/dev_appserver_import_hook.py", line 592, in __init__ 
    raise IOError(errno.EACCES, 'file not accessible', filename) 
IOError: [Errno 13] file not accessible: '/dev/urandom' 
ERROR 2012-06-29 16:04:20,721 webapp2.py:1549] Exception 
ERROR 2012-06-29 16:04:20,721 webapp2.py:1549] AttributeError 
ERROR 2012-06-29 16:04:20,721 webapp2.py:1549] : 
ERROR 2012-06-29 16:04:20,721 webapp2.py:1549] "'DevURandomRNG' object has no attribute 'closed'" 
ERROR 2012-06-29 16:04:20,721 webapp2.py:1549] in 
ERROR 2012-06-29 16:04:20,721 webapp2.py:1549] <bound method DevURandomRNG.__del__ of <Crypto.Random.OSRNG.posix.DevURandomRNG object at 0x52707d0>> 
ERROR 2012-06-29 16:04:20,721 webapp2.py:1549] ignored 

被引发错误的Python代码是在该块中的第二行：

from Crypto.Cipher import AES 
from Crypto import Random 

key = b'Sixteen byte key' 
iv = Random.new().read(AES.block_size) 
cipher = AES.new(key, AES.MODE_CBC, iv) 
return iv + cipher.encrypt(plaintext) 

看到这种错误，I realized it might be a permissions error后。然后我做了一个快速检查/ dev/urandom的权限：

eric@eric-Latitude-E5400 ~ $ dpkg -L udev | xargs grep urandom 
/lib/udev/rules.d/50-udev-default.rules:KERNEL=="null|zero|full|random|urandom", MODE="0666" 
eric@eric-Latitude-E5400 ~ $ ls -lart /dev/*random 
crw-rw-rw- 1 root root 1, 9 Jun 29 10:53 /dev/urandom 
crw-rw-rw- 1 root root 1, 8 Jun 29 10:53 /dev/random 

因此，它看起来像我的权限很好。我也尝试以root用户身份运行开发服务器，但是我得到了同样的错误。出于某种原因，这只发生在开发服务器上，而不是部署到谷歌的云中。关于下一步尝试的任何想法？

谢谢！

Answer 1

您得到的错误是因为GAE限制文件访问，并且/dev/urandom被阻止。

注意，错误是不是当你导入PyCrypto，这是当你做AES.new(key, AES.MODE_CBC, iv)

你能解决这个问题，通过编辑Crypto/Random/OSRNG/__init__.py和移动线

if hasattr(os, 'urandom'): 
    from Crypto.Random.OSRNG.fallback import new 

到顶部，或在脚本的开头将os.name修改为与posix或nt不同的内容。我建议第一个选项。

ps：我以为你使用python 2.5和pycrypto 2.2，因为你的Traceback。下次请包括这些详细信息。