Actually, the NTP authentication key in the config is done with Cisco's level 7 password cipher, so it is crackable with the IOS password cracker. It is necessary that this key be kept in a reversable form as we will need it to generate a proper MD5 hash on the wire. On the wire, the key will be hashed using he MD5 one way hashing algorithm. While collisions has recently been found in this algorithm, it is not "crackable" per se. By definition, these hashes cannot be reversed.
