Loading...

Improvement of a Lattice-based Functional Encryption Scheme

Kosari, Mohamad Hossein | 2024

0 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57384 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Eghlidos, Taraneh; Mohajeri, Javad
  7. Abstract:
  8. Functional Encryption (FE) is an advanced public key encryption primitive that allows fine-grained control over encrypted data. In many applications, we need to embed an access policy into the secret keys, and also during decryption, only the result of a linear function on the data is revealed, not the data itself. Although FE schemes for general functionalities are proposed, these schemes are either not efficient or their security relies on non-standard assumptions. So far, two attribute-based inner-product functional encryption (AB-IPFE) schemes for inner-product of short integer vectors with security upon LWE assumption has been proposed, which makes them post-quantum secure. These schemes can be a better solution to the above scenario, but they only provide selective security. In the security proof of these schemes, the challenger embeds the challenge attribute in the master public key in order to answer the adversary’s secret key queries without having a trapdoor. In this thesis, by existing ideas, we show how to do this embedding indirectly and delay the need to know the challenge attribute until generating the first secret key, thus improving the security to semi-adaptive security. With this security improvement, the size of the attribute encoding parts in the ciphertext doubles, but the sizes of the secret key and master public key remain almost unchanged. Also, the proposed scheme still inherits the properties of the underlying schemes: supports the access policies of class of general circuits (with polynomially unbounded size) with bounded depth, and the secret keys are short and their size depends only on the depth of the policy circuit rather than its size. Another problem in this thesis is key delegation in AB-IPFE that to the best of our knowledge has not been considered so far. This capability can be useful in situations where people use multiple devices or want to delegate the ability to decrypt and doing some duties to others. We formally define this capability in AB-IPFE systems and try to realize it by testing some lattice trapdoor delegation techniques. Since these techniques are not developed enough to consider both ABE and IPFE security simultaneously, this attempt is not successful
  9. Keywords:
  10. Lattice-Based Cryptography ; Attribute Based Encryption ; Key Delegation ; Inner-Product Functional Encryption ; Attribute-Based Inner-Product Functional Encryption ; Semi-Adaptive Security

 Digital Object List

 Bookmark

...see more