Biblio

Most common user authentication methods use some form of password or a combination of passwords. However, encryption schemes are generally not directly compatible with user passwords and thus, Password-Based Key Derivation Functions (PBKDFs) are used to convert user passwords into cryptographic keys. In this paper, we analyze the theoretical security of PBKDF2 and present two vulnerabilities, γ-collision and δ-collision. Using AES-128 as our exemplar, we show that due to γ-collision, text encrypted with one user password can be decrypted with γ 1 different passwords. We also provide a proof that finding− a collision in the derived key for AES-128 requires δ lesser calls to PBKDF2 than the known Birthday attack. Due to this, it is possible to break password-based AES-128 in O(264) calls, which is equivalent to brute-forcing DES.

The usage of cloud for data storage has become ubiquitous. To prevent data leakage and hacks, it is common to encrypt the data (e.g. PDF files) before sending it to a cloud. However, this limits the search for specific files containing certain keywords over an encrypted cloud data. The traditional method is to take down all files from a cloud, store them locally, decrypt and then search over them, defeating the purpose of using a cloud. In this paper, we propose a method, called SecureCSearch, to perform keyword search operations on the encrypted PDF files over cloud in an efficient manner. The proposed method makes use of Shamir's Secret Sharing scheme in a novel way to create encrypted shares of the PDF file and the keyword to search. We show that the proposed method maintains the security of the data and incurs minimal computation cost.