The Collaborative International Dictionary of English v.0.48:

Decipherer \De*ci"pher*er\, n.
   One who deciphers.
   [1913 Webster]

WordNet (r) 3.0 (2006):

decipherer
    n 1: the kind of intellectual who converts messages from a code
         to plain text [syn: decoder, decipherer]
    2: a reader capable of reading and interpreting illegible or
       obscure text