- This paper proposes a Hash Chain algorithm to create a key safer than the existing encryption method, and suggests an encryption method of higher security than the existing system by using the encryption method which applies each key created through the Hash Chain algorithm to each block. Also, after users are authenticated through on/off line key authentication, keys fragmented by using a key fragmentation method are encoded and each fragment is sent to a client. Thus, when this proposed method is used, even when keys are let out, it will be difficult to get the complete set of keys. After the proposed system is designed and realized, an experiment was carried out by using digital contents files of a variety of size for the performance evaluation and it was found that the proposed system was about to do a safer key transmission than the existing system. Here the whole data was encrypted in a way not to be decoded even when key fragments are stolen. Also, in the client system, it was...