From: Daira Hopwood <daira@jacaranda.org>
Date: Mon, 24 Feb 2014 20:23:39 +0000 (+0000)
Subject: Use bigger random one-time keys in timing_safe_compare. fixes #2165
X-Git-Tag: allmydata-tahoe-1.10.1a1~200
X-Git-Url: https://git.rkrishnan.org/%5B/%5D%20/uri/%22doc.html/COPYING.GPL?a=commitdiff_plain;h=6ca5f5fc39650de55c9d93ceef5f275b80a100d1;p=tahoe-lafs%2Ftahoe-lafs.git

Use bigger random one-time keys in timing_safe_compare. fixes #2165

Follows this advice from Marsh Ray and Solar Designer: https://twitter.com/zooko/status/431105294777597952

Signed-off-by: Daira Hopwood <daira@jacaranda.org>
---

diff --git a/src/allmydata/util/hashutil.py b/src/allmydata/util/hashutil.py
index 546dc0b0..81522ad5 100644
--- a/src/allmydata/util/hashutil.py
+++ b/src/allmydata/util/hashutil.py
@@ -203,7 +203,7 @@ def ssk_storage_index_hash(readkey):
     return tagged_hash(MUTABLE_STORAGEINDEX_TAG, readkey, KEYLEN)
 
 def timing_safe_compare(a, b):
-    n = os.urandom(8)
+    n = os.urandom(32)
     return bool(tagged_hash(n, a) == tagged_hash(n, b))
 
 BACKUPDB_DIRHASH_TAG = "allmydata_backupdb_dirhash_v1"