This occurs when a bank changes its current codes. In the middle of efficiency period of a group of codes the next group starts. Therefor, at all times two groups of suitable codes exist. The first is getting old and the second is new. Therefore, the client has enough time to spend the digital money on a paybook or change to more current codes.
Data transferred by the web is encoded by common cryptofraphy methods.
Public keys of 1024 bits and symmetric keys of 160 bits are used. This ensures that the decoding of encoded messages is impossible in the foreseeable future. All system participants have good probative evidence - the digital signatures of all financial transaction participants. RSA algorithms are used. Stability of connection.