The Collaborative International Dictionary of English v.0.48:

Cryptographic \Cryp`to*graph"ic\ (kr?p`t?-gr?f"?k),
Cryptographical \Cryp`to*graph"ic*al\ (kr?p`t?-gr?f"?-kal), a.
   Relating to cryptography; written in secret characters or in
   cipher, or with sympathetic ink.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cryptographical
    adj 1: of or relating to cryptanalysis [syn: cryptanalytic,
           cryptographic, cryptographical, cryptologic,
           cryptological]