From The Collaborative International Dictionary of English v.0.48 [gcide]:
Decipherable \De*ci"pher*a*ble\, a.
Capable of being deciphered; as, old writings not
decipherable.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
decipherable
adj 1: easily deciphered [syn: clear, decipherable,
readable]