From: Zooko O'Whielacronx <zooko@zooko.com>
Date: Sun, 5 Jul 2009 02:48:15 +0000 (-0700)
Subject: directories: make the IV for the writecaps in directory entries be computed from... 
X-Git-Tag: trac-4000~24
X-Git-Url: https://git.rkrishnan.org/pf/content/en/nxhtml.html?a=commitdiff_plain;h=786ed012b3510135c60769e6d5e91d6f3fef2725;p=tahoe-lafs%2Ftahoe-lafs.git

directories: make the IV for the writecaps in directory entries be computed from the secure hash of the writecap itself
This makes encoding of directory entries deterministic, and it is also a tad faster on Macbook Pro than getting a random IV with os.urandom(16).
---

diff --git a/src/allmydata/dirnode.py b/src/allmydata/dirnode.py
index 302f8df5..851ec4bf 100644
--- a/src/allmydata/dirnode.py
+++ b/src/allmydata/dirnode.py
@@ -195,7 +195,7 @@ class NewDirectoryNode:
 
     def _encrypt_rwcap(self, rwcap):
         assert isinstance(rwcap, str)
-        IV = os.urandom(16)
+        IV = hashutil.mutable_rwcap_iv_hash(self._node.get_writekey())
         key = hashutil.mutable_rwcap_key_hash(IV, self._node.get_writekey())
         cryptor = AES(key)
         crypttext = cryptor.process(rwcap)
diff --git a/src/allmydata/util/hashutil.py b/src/allmydata/util/hashutil.py
index d5b260ad..8987d2dc 100644
--- a/src/allmydata/util/hashutil.py
+++ b/src/allmydata/util/hashutil.py
@@ -82,6 +82,7 @@ MUTABLE_STORAGEINDEX_TAG = "allmydata_mutable_readkey_to_storage_index_v1"
 
 # dirnodes
 DIRNODE_CHILD_WRITECAP_TAG = "allmydata_mutable_writekey_and_salt_to_dirnode_child_capkey_v1"
+DIRNODE_CHILD_IV_TAG = "allmydata_mutable_writekey_to_iv_v1"
 
 def storage_index_hash(key):
     # storage index is truncated to 128 bits (16 bytes). We're only hashing a
@@ -122,6 +123,7 @@ def plaintext_segment_hasher():
     return tagged_hasher(PLAINTEXT_SEGMENT_TAG)
 
 KEYLEN = 16
+IVLEN = 16
 
 def convergence_hash(k, n, segsize, data, convergence):
     h = convergence_hasher(k, n, segsize, convergence)
@@ -170,6 +172,8 @@ def hmac(tag, data):
 
 def mutable_rwcap_key_hash(iv, writekey):
     return tagged_pair_hash(DIRNODE_CHILD_WRITECAP_TAG, iv, writekey, KEYLEN)
+def mutable_rwcap_iv_hash(writekey):
+    return tagged_hash(DIRNODE_CHILD_IV_TAG, writekey, IVLEN)
 
 def ssk_writekey_hash(privkey):
     return tagged_hash(MUTABLE_WRITEKEY_TAG, privkey, KEYLEN)