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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,126 @@ | ||
| import os | ||
| import base64 | ||
| import hashlib | ||
| from zope.interface import ( | ||
| Interface, | ||
| Attribute, | ||
| implementer, | ||
| ) | ||
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| class IPermission(Interface): | ||
| """ | ||
| A server-side method of granting permission to a client. | ||
| """ | ||
| name = Attribute("name") | ||
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| def get_welcome_data(): | ||
| """ | ||
| return a dict of information to include under the name of this | ||
| Permission granter (under "permission-required" in the Welcome) | ||
| """ | ||
|
|
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| def verify_permission(submit_permission): | ||
| """ | ||
| return a bool indicating if the submit_permission data is a valid | ||
| permission (or not) | ||
| """ | ||
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| def create_permission_provider(kind): | ||
| """ | ||
| returns a permissions-provider | ||
| """ | ||
| if kind == "none": | ||
| return NoPermission | ||
| elif kind == "hashcash": | ||
| return HashcashPermission | ||
| raise ValueError( | ||
| "Unknown permission provider '{}'".format(kind) | ||
| ) | ||
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| @implementer(IPermission) | ||
| class NoPermission(object): | ||
| """ | ||
| A no-op permission provider used to grant any client access (the | ||
| default). | ||
| """ | ||
| name = "none" | ||
|
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| def get_welcome_data(self): | ||
| return {} | ||
|
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| def verify_permission(self, submit_permission): | ||
| return True | ||
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| @implementer(IPermission) | ||
| class HashcashPermission(object): | ||
| """ | ||
| A permission provider that generates a random 'resource' string | ||
| and checks a proof-of-work from the client. | ||
| """ | ||
| name = "hashcash" | ||
|
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| def __init__(self, bits=20): | ||
| self._bits = bits | ||
|
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| def get_welcome_data(self): | ||
| """ | ||
| Generate the data to include under this method's key in the | ||
| `permission-required` value of the welcome message. | ||
| Should be called at most once per connection. | ||
| """ | ||
| self._hashcash_resource = base64.b64encode(os.urandom(8)).decode("utf8") | ||
| return { | ||
| "bits": self._bits, | ||
| "resource": self._hashcash_resource, | ||
| } | ||
|
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||
| def verify_permission(self, perms): | ||
| """ | ||
| :returns bool: an indication of whether the provided permissions | ||
| reply from a client is valid | ||
| """ | ||
| # XXX THINK do we need this whole method to be constant-time? | ||
| # (basically impossible if it's not even syntactially valid?) | ||
| stamp = perms.get("stamp", "") | ||
| fields = stamp.split(":") | ||
| if len(fields) != 7: | ||
| return False | ||
| vers, claimed_bits, date, resource, ext, rand, counter = fields | ||
| vers = int(vers) | ||
| if vers != 1: | ||
| return False | ||
| if resource != self._hashcash_resource: | ||
| return False | ||
|
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| claimed_bits = int(claimed_bits) | ||
| if claimed_bits < self._bits: | ||
| return False | ||
|
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| h = hashlib.sha1() | ||
| h.update(stamp.encode("utf8")) | ||
| measured_hash = h.digest() | ||
| if leading_zero_bits(measured_hash) < claimed_bits: | ||
| return False | ||
| return True | ||
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| def leading_zero_bits(bytestring): | ||
| """ | ||
| :returns int: the number of leading zeros in the given byte-string | ||
| """ | ||
| measured_bits = 0 | ||
| for byte in bytestring: | ||
| bit = 1 << 7 | ||
| while bit: | ||
| if byte & bit: | ||
| return measured_bits | ||
| else: | ||
| measured_bits += 1 | ||
| bit = bit >> 1 | ||
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