Multicloud Storage

Another alternative to secure private keys against loss or theft would be to rely on multicloud storage systems. Multicloud storage systems typically rely on a number of commodity cloud providers (e.g., Amazon, Google) with the goal of distributing trust across different administrative domains. This model is receiving increasing attention nowadays with leading cloud storage providers such as EMC, IBM, and Microsoft, offering products for multicloud systems [26].

Here, the private keys could be secret-shared and each share can be stored across multiple clouds. Recall that secret-sharing schemes allows a user to distribute a secret among a number of entities, such that only authorized subsets of shareholders can reconstruct the secret. In threshold secret-sharing schemes, the user can define a threshold t such that any t out of n shares can reconstruct the secret. Secret-sharing guarantees security against a nonauthorized subset of shareholders; the combination of any 0 < m < t shares does not leak any meaningful information about the secret [27-29].

By secret-sharing the private keys in a multicloud storage system, the security of the private keys is ensured unless t or more cloud operators collude. Moreover, such a solution resists against the failure of up to (n - t) clouds. Note that applications for multicloud storage systems can be made available on all devices of the users, thereby allowing users to seamlessly synchronize their keys across

Table 7.1

Provisions of Alternatives to Secure Bitcoin Wallets

their devices. Table 7.1 summarizes the provisions of the investigated alternatives to secure Bitcoin wallets.