## Tokyo QKD Network for Long-Lived Systems

##### Masahide Sasaki

We present one possible solution for long-lived systems which can archive digital data with long-term confidentiality and integrity as well as high availability (such as data backup) and useful functionality (computation over encrypted data). Our solution is a distributed storage network system based on Shamirâ€™s (k, n)-threshold secret sharing scheme, in which the data are split into n pieces (shares) for storage and at least k pieces of them must be gathered for reconstruction. Storage servers are linked via private channels, which are realized by encryption with information theoretically secure keys supplied from quantum key distribution (QKD) network. The Shamirâ€™s threshold secret sharing scheme can ensure information theoretical security, provided that they could collect shares of less than the threshold k. It also allows addition and multiplication of the shares. Thus by using these elements, we can realize long-term confidentiality, availability, and computation over the shares.

To ensure long-term integrity, both computationally and information theoretically secure authentication schemes can be used. We propose an example for the latter case, which is based on a single-password authentication using randomization with keys from the QKD network.

In the presentation, we describe the basic layered structure of the Tokyo QKD Network, and how a long-lived system can be constructed with it. We also analyze the total performances of the long-lived system, such as allowed data size, in terms of the QKD key rate.