Here I use a Threefish kernel module with CBC mode. But there is no hash function that can supply a IV with Threefish block size (1024-bits), so I use a 64-bit random IV inserted in the dm-crypt with cryptsetup --skip option.
I know that the ideal size for an IV in CBC encryption is the same size of the block, but, what would be the consequences of using an IV smaller that the block size in CBC encryption?
PS.: I keep my IV secret (it's used in a command line inside a shell script).