From 7e77801aa4996f6afdd70d190932a9ae9c5ec82a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philipp=20H=C3=B6rist?= <philipp@hoerist.com>
Date: Fri, 17 Jan 2020 22:40:45 +0100
Subject: [PATCH] [omemo] Add back 12 byte IV read support for aesgcm links
---
omemo/file_crypto.py | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/omemo/file_crypto.py b/omemo/file_crypto.py
index 8419155c..37d40a26 100644
--- a/omemo/file_crypto.py
+++ b/omemo/file_crypto.py
@@ -169,10 +169,19 @@ class FileDecryption:
raise ValueError('Invalid fragment')
fragment = binascii.unhexlify(fragment)
- key = fragment[16:]
- iv = fragment[:16]
- if len(key) != 32 or len(iv) != 16:
- raise ValueError('Invalid fragment')
+ size = len(fragment)
+ # Clients started out with using a 16 byte IV but long term
+ # want to swtich to the more performant 12 byte IV
+ # We have to support both
+ if size == 48:
+ key = fragment[16:]
+ iv = fragment[:16]
+ elif size == 44:
+ key = fragment[12:]
+ iv = fragment[:12]
+ else:
+ raise ValueError('Invalid fragment size: %s' % size)
+
return key, iv
@staticmethod
--
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