2 random character.

Dear Mr, Guru, Rabbi, teacher, of excel :

i have a cell say from a1 to a4.
ab
ac
ad
ae

id like to combine it to 2 random character so from b1 to b4 will be :
o-ab-g
a-ac-h
g-ad-j
e-ae-7

where the first and the last character will be randomize

Regards,
Hong