[tor-commits] [stem/master] Drop _get_padding_needed()

[atagar at torproject.org]

commit d313aca7ec142e7be1ba00517f4bd12b535cea5e
Author: Damian Johnson <atagar at torproject.org>
Date:   Sun Nov 10 17:22:02 2019 -0800

    Drop _get_padding_needed()
    
    Maybe I'm missing something, but why not simply pad using the modulus?
---
 stem/descriptor/hidden_service.py |  6 ++--
 stem/descriptor/hsv3_crypto.py    | 61 ---------------------------------------
 2 files changed, 4 insertions(+), 63 deletions(-)

diff --git a/stem/descriptor/hidden_service.py b/stem/descriptor/hidden_service.py
index ab377728..141f54b0 100644
--- a/stem/descriptor/hidden_service.py
+++ b/stem/descriptor/hidden_service.py
@@ -931,8 +931,10 @@ def _get_superencrypted_blob(intro_points, descriptor_signing_privkey, revision_
 
   middle_descriptor_layer = _get_middle_descriptor_layer_body(inner_ciphertext_b64)
 
-  padding_bytes_needed = stem.descriptor.hsv3_crypto._get_padding_needed(len(middle_descriptor_layer))
-  middle_descriptor_layer = middle_descriptor_layer + b'\x00' * padding_bytes_needed
+  # Spec mandated padding: "Before encryption the plaintext is padded with NUL
+  # bytes to the nearest multiple of 10k bytes."
+
+  middle_descriptor_layer = middle_descriptor_layer + b'\x00' * (len(middle_descriptor_layer) % 10000)
 
   return b'\n' + _encrypt_layer(middle_descriptor_layer, b'hsdir-superencrypted-data', revision_counter, subcredential, blinded_key)
 
diff --git a/stem/descriptor/hsv3_crypto.py b/stem/descriptor/hsv3_crypto.py
index b762c5ee..0186ba90 100644
--- a/stem/descriptor/hsv3_crypto.py
+++ b/stem/descriptor/hsv3_crypto.py
@@ -64,64 +64,3 @@ class HSv3PrivateBlindedKey(object):
 
   def sign(self, msg):
     return signatureWithESK(msg, self.blinded_secret_key, self.blinded_pubkey)
-
-
-"""
-Basic descriptor logic:
-
-       SALT = 16 bytes from H(random), changes each time we rebuld the
-              descriptor even if the content of the descriptor hasn't changed.
-              (So that we don't leak whether the intro point list etc. changed)
-
-       secret_input = SECRET_DATA | subcredential | INT_8(revision_counter)
-
-       keys = KDF(secret_input | salt | STRING_CONSTANT, S_KEY_LEN + S_IV_LEN + MAC_KEY_LEN)
-
-       SECRET_KEY = first S_KEY_LEN bytes of keys
-       SECRET_IV  = next S_IV_LEN bytes of keys
-       MAC_KEY    = last MAC_KEY_LEN bytes of keys
-
-
-Layer data:
-
- 2.5.1.1. First layer encryption logic
-     SECRET_DATA = blinded-public-key
-     STRING_CONSTANT = "hsdir-superencrypted-data"
-
- 2.5.2.1. Second layer encryption keys
-     SECRET_DATA = blinded-public-key | descriptor_cookie
-     STRING_CONSTANT = "hsdir-encrypted-data"
-"""
-
-SALT_LEN = 16
-MAC_LEN = 32
-
-S_KEY_LEN = 32
-S_IV_LEN = 16
-MAC_KEY_LEN = 32
-
-"""
-Descriptor encryption
-"""
-
-
-def ceildiv(a, b):
-  """
-  Like // division but return the ceiling instead of the floor
-  """
-
-  return -(-a // b)
-
-
-def _get_padding_needed(plaintext_len):
-  """
-  Get descriptor padding needed for this descriptor layer.
-  From the spec:
-     Before encryption the plaintext is padded with NUL bytes to the nearest
-     multiple of 10k bytes.
-  """
-
-  PAD_MULTIPLE_BYTES = 10000
-
-  final_size = ceildiv(plaintext_len, PAD_MULTIPLE_BYTES) * PAD_MULTIPLE_BYTES
-  return final_size - plaintext_len