[guardian-dev] SQLCipher adopted by WeChat and their 300M users

[Nathan of Guardian]

Through some of our own recent sluething, Citizen Lab's research into
"Asia Chats" security, and now via this third-party post, it has been
recently discovered that WeChat for Android uses SQLCipher for local
data encryption in its app.

http://blog.emaze.net/2013/09/a-look-at-wechat-security.html

Now, as with most things WeChat, the actually implementation is not that
ideal, utilizing a short key, generated in part from the device's ID,
and some sort of server provided token. Still, at least they tried, and
SQLCipher is considered stable enough to run on 300 million devices
around the world.

Who knows, maybe the devs are on this list or the SQLCipher list, and we
can help them improve there implementation using CacheWord!

More from the emaze post below...
*****

WeChat locally stores application data in an encrypted SQLite database
named "EnMicroMsg.db". This database is located in the "MicroMsg"
subfolder inside the application's data directory (typically something
like "/data/data/com.tencent.mm").

The database is encrypted using SQLCipher, an open source extension for
SQLite that provides full database encryption. The encryption password
is derived from the "uin" parameter (see previous sections) combined
with the device identifier through a custom function. More precisely,
the key generation function leverages the mangle() function shown in the
previous Python snippet. The actual database encryption key can be
generated through the following pseudo-code:

password = mangle(deviceid + uin)[:7]

Here deviceid is the value returned by the Android API function
TelephonyManager.getDeviceId(). Follows a sample SQLCipher console
session that demonstrate how the EnMicroMsg.db database can be decrypted.

$ sqlcipher EnMicroMsg.db
sqlite> PRAGMA key = 'b60c8e4';
sqlite> PRAGMA cipher_use_hmac = OFF;
sqlite> .schema
CREATE TABLE conversation (unReadCount INTEGER, status INT, ...
CREATE TABLE bottleconversation (unReadCount INTEGER, status INT, ...
CREATE TABLE tcontact (username text PRIMARY KEY, extupdateseq long, ...
...

It is also worth pointing out that, as the key generation algorithm
truncates the password to 7 hex characters, it would be not so difficult
for motivated attackers who are able to get the encrypted database to
brute force the key, even without knowing the uin or the device identifier.