Each octet in this object contains
a group number, corresponding to a Diffie-Hellman
group identifier, in order of preference.
Currently there are 5 groups supported,
from value 0 through 4.
Each number corresponds to the Diffie-Hellman group
as follows -
0 - DH_NULL
1 - DH_1024
2 - DH_1280
3 - DH_1536
4 - DH_2048