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Secure, Policy-Based, Multi-Recipient Data Sharing

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Doctoral thesis

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In distributed systems users often need to share sensitive data with other users based on the latter s ability to satisfy various policies. In many cases the data owner may not even know the identities of the data recipients, but deems it crucial that they are legitimate i.e., satisfy the policy. Enabling such data sharing over the Internet faces the challenge of 1 securely associating access policies with data and enforcing them, and 2 protecting data as it traverses untrusted proxies and intermediate repositories. Furthermore, it is desirable to achieve properties such as 1 flexibility of access policies 2 privacy of sensitive access policies 3 minimal reliance on trusted third parties and 4 efficiency of access policy enforcement. Often schemes enabling controlled data sharing need to trade one property for another. In this dissertation, we propose two complimentary policy-based data sharing schemes that achieve different subsets of the above desired properties. In the first part of this dissertation, we focus on CiphertextPolicy Attribute-Based Encryption CP-ABE schemes that specify and enforce access policies cryptographically and eliminate trusted mediators. We motivate the need for flexible attribute organization within user keys for efficient support of many practical applications. We then propose Ciphertext-Policy Attribute-Set Based Encryption CP-ASBE which is the first CP-ABE scheme to 1 efficiently support naturally occurring compound attributes, 2 support multiple numerical assignments for a given attribute in a single key and 3 provide efficient key management. While the CP-ASBE scheme minimizes reliance on trusted mediators, it can support neither context-based policies nor policy privacy.

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  • Information Science

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