Mount / decrypt aes overlay knoppix-data partition

I want to decrypt to raw or mount one aes encrypted overlay partition created with Knoppix 7.6.0. Password is known.
The partition has a broken file system (reiserfs), so normal boot halt with a fail message from UNIONFS.
I want to mount it after I start with noimage option or on another installation and try to fix it. The partition was damaged after copied a large file who exceeded capacity.

Any idea are welcome. Thank you.

Solved.
Overlay partition is plain.

su
cryptsetup plainOpen --cipher aes /dev/sdb2 enc
<enter your password>
mount /dev/mapper/enc /media/sdb2
<copy data>
umount /media/sdb2
cryptsetup close enc

Partition has been fixed by simple removing the large file. It was an image who was accidently saved into home.
However USB has been recreated ;-)