Compute the Authenticator length
Authenticator : 0x62 L1 Authenticator [APPLICATION 2] | +--> 0x30 L2 Authenticator SEQUENCE | +--> 0xA0 03 authenticator-vno tag | | | +--> 0x02 0x01 0x05 authenticator-vno (int, 5) | +--> 0xA1 L3 crealm tag | | | +--> 0x1B L3-1 crealm (KerberosString) | +--> 0xA2 L4 cname (PrincipalName) | +--> 0xA3 L5 cksum (CheckSum) | +--> 0xA4 L6 cusec tag | | | +--> 0x02 L6-1 nnn cusec value (Integer) | +--> 0xA5 0x11 ctime tag | | | +--> 0x18 0x0F ttt ctime (KerberosTime) | +--> 0xA6 L7 subkey (EncryptionKey) | +--> 0xA7 L8 seq-number tag | | | +--> 0x02 L8-1 nnn seq-number (Integer) | +--> 0xA8 L9 authorization-data (AuthorizationData)