Crypto Algorithm Question - Passphrase hash length shorter than cipher key

Hi,

I'm looking to use dm-crypt / cryptsetup (not LUKS) on Linux to encrypt a filesystem on a small loopback file.
The version of cryptsetup I'm using is 1.3.1 which defaults to:

Hash: ripemd160
Cipher: aes-cbc-essiv:sha256, 256 bit key

The question I have is, if the output of the hash is 160 bits and the cipher takes 256, then to make the key, 96 bits must be padded in a (presumably) determinable manner. Does this not weaken the cipher? I know the result is probably still mega secure but why compromise?

Thanks

There doesn't need to be any padding. For example, the PBKDF2 algorithm from PKCS#5 hashes the pass phrase plus a counter multiple times to produce an arbitrarily long output.

Hi,
Can't you use SHA256 instead of RIPEMD160 ?