Symmetric encryption with a key size less than 128bit

Symmetric encryption with a key size less than 128bit

I'm implementing a cartographic solution for Wireless and sensor network
security. So in a one step of this implementation sensor nodes have a
certificate of a CA. Sensors are supposed to generate a symmetric key and
encrypt it with CA's public key and send it to the CA.
I use openssl for certificate and key generations. I though of using AES
with 128bit key for the symmetric key. The problem for the moment is that
I can't encrypt 128bit data as follows since it gives "Data is too large"
error.
openssl rsautl -encrypt -inkey id_rsa.pub.pem -pubin -in key1.bin -out
key1.bin.enc
So it loks like either I need to encrypt 128 bit key using another way or
I can use a smaller key which in sensor network environment will not be a
problem.
My question is "Is there any symmetric key encryption with smaller key or
do I have a way to encrypt 128bit key using the certificate directly"
Thank you