From: avital sela <avitalsela95@gmail.com>
Subject: question about fragmentation of large packets
Date: Tue, 8 Dec 2009 14:54:43 +0200
Message-ID: <311e0d1f0912080454q6099cc4cq5b23617364bf9633@mail.gmail.com>
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To: linux-crypto@vger.kernel.org, herbert@gondor.apana.org.au
Sender: linux-crypto-owner@vger.kernel.org

Hello,

I am testing a AES HW crypto driver I wrote. I test by setting up a
tunnel between the board and a Linux server and pinging packets from
the board to the server.
With my driver loaded everything works fine with small packets but
large packets (>1500) fail (100% packet loss).
I added some debug code to the standard crypto/cbc.c and noticed that
when I ping using -s1500 the encryption (aes-cbc) gets broken up to 3
chuncks
sized 1456 , 16, 64.  I also noticed that the iv for each of the
chunks is different.
Questions:
1. Why are there 3 chunks with these sizes? Is this related to the
crypto subsystem or the  ipsec one?
2. How is the iv computed between each subsequent chunk?
I think my driver is failing because although it also processes 3
identically sized chunks it does not change the iv between each one
(it only does so once at the end).

Thanks for your time,
Avital