Time-Specific Encryption

This paper introduces and explores the new concept of Time-Specific Encryption (TSE). In (Plain) TSE, a Time Server broadcasts a key at the beginning of each time unit, a Time Instant Key (TIK). The sender of a message can specify any time interval during the encryption process; the receiver can decrypt to recover the message only if it has a TIK that corresponds to a time in that interval. We extend Plain TSE to the public-key and identity-based settings, where receivers are additionally equipped with private keys and either public keys or identities, and where decryption now requires the use of the private key as well as an appropriate TIK. We introduce security models for the plain, public-key and identity-based settings. We also provide constructions for schemes in the different settings, showing how to obtain Plain TSE using identity-based techniques, how to combine Plain TSE with public-key and identity-based encryption schemes, and how to build schemes that are chosen-ciphertext secure from schemes that are chosen-plaintext secure. Finally, we suggest applications for our new primitive, and discuss its relationships with existing primitives, such as Timed Release Encryption and Broadcast Encryption

Time-Specific Encryption with Constant-Size Secret-Keys Secure under Standard Assumption

In Time-Specific Encryption (TSE) [Paterson and Quaglia, SCN\u2710] system, each secret-key (resp. ciphertext) is associated with a time period t s.t. 0<=t<=T-1 (resp. a time interval [L,R] s.t. 0<=L<=R<=T-1. A ciphertext under [L,R] is correctly decrypted by any secret-key for any time t included in the interval, i.e., L<=t<=R. TSE\u27s generic construction from identity-based encryption (IBE) (resp. hierarchical IBE (HIBE)) from which we obtain a concrete TSE scheme with secret-keys of O(log T)|g| (resp. O(log^2 T)|g|) and ciphertexts of size O(log T)|g| (resp. O(1)|g|) has been proposed in [Paterson and Quaglia, SCN\u2710] (resp. [Kasamatsu et al., SCN\u2712]), where |g| denotes bit length of an element in a bilinear group G. In this paper, we propose another TSE\u27s generic construction from wildcarded identity-based encryption (WIBE). Differently from the original WIBE ([Abdalla et al., ICALP\u2706]), we consider WIBE w/o (hierarchical) key-delegatability. By instantiating the TSE\u27s generic construction, we obtain the first concrete scheme with constant-size secret-keys secure under a standard (static) assumption. Specifically, it has secret-keys of size O(1)|g| and ciphertexts of size O(log^2 T)|g|, and achieves security under the decisional bilinear Diffie-Hellman (DBDH) assumption

A Survey: Attribute Based Encryption for Secure Cloud

Cloud computing is an enormous area which shares huge amount of data over cloud services and it has been increasing with its on-demand technology. Since, with these versatile cloud services, when the delicate data stored within the cloud storage servers, there are some difficulties which has to be managed like its Security Issues, Data Privacy, Data Confidentiality, Data Sharing and its integrity over the cloud servers dynamically. Also, the authenticity and data access control should be maintained in this wide environment. Thus, Attribute based Encryption (ABE) is a significant version of cryptographic technique in the cloud computing environment. Public Key Encryption acts as the basic technique for ABE where it provides one to many encryptions, here, the private key of users &amp; the cipher-text both rely on attributes such that, when the set of the attributes of users key matches set of attributes of cipher-text with its corresponding access policy, only then decryption is possible. Thus, an opponent could grant access to the sensitive information that holds multiple keys, if it has at least one individual key for accession. The techniques based on ABE consist of two types: KP-ABE (Key- Policy ABE) where the user’s private key is linked to an access structure (or access policy) over attributes and cipher-text is connected to the set of attributes, and CP-ABE (cipher-text policy ABE) is vice versa. Hence, in this, Review we discuss about the various security techniques and relations based on Attributes Based Encryption, especially, the type KP-ABE over data attributes which explains secured methods &amp; its schemes related to time specifications.&nbsp

On the Use of Key Assignment Schemes in Authentication Protocols

Key Assignment Schemes (KASs) have been extensively studied in the context of cryptographically-enforced access control, where derived keys are used to decrypt protected resources. In this paper, we explore the use of KASs in entity authentication protocols, where we use derived keys to encrypt challenges. This novel use of KASs permits the efficient authentication of an entity in accordance with an authentication policy by associating entities with security labels representing specific services. Cryptographic keys are associated with each security label and demonstrating knowledge of an appropriate key is used as the basis for authentication. Thus, by controlling the distribution of such keys, restrictions may be efficiently placed upon the circumstances under which an entity may be authenticated and the services to which they may gain access. In this work, we explore how both standardized protocols and novel constructions may be developed to authenticate entities as members of a group associated to a particular security label, whilst protecting the long-term secrets in the system. We also see that such constructions may allow for authentication whilst preserving anonymity, and that by including a trusted third party we can achieve the authentication of individual identities and authentication based on timestamps without the need for synchronized clocks

A Novel Technique for Cloud Computing Data Security and Public Auditing

In prior years, the fast improvement of cloud storage services makes it simpler than at any other time for cloud clients to disseminate information (data) with everyone. To ensure client's trust in the dependability of their public information on the cloud, various strategies have been proposed for information trustworthiness assessing with spotlights on different viable components, secure data destructing, public integrity auditing and so forth.. Since it is not achievable to execute full lifecycle protection security, access control turns into a testing assignment, particularly when we share delicate information on cloud servers. To handle this issue, proposed framework presents a key strategy trait based encryption with time-determined properties (KP-TSABE), another safe information self-destructing framework in distributed computing. Moreover open respectability inspecting frameworks presented for cloud information sharing administrations that check the uprightness of client's delicate information being put away in the cloud. In the KP-TABE plan, each figure content is marked with a period interim while the private key is connected with a period moment. The figure message just is unscrambled if both the time instant is in the permitted time interim and traits which are connected with the figure content guarantee the key's entrance structure. Also, Third Party Auditing (TPA) is acquainted with help clients to assess the danger of their subscribed cloud data administrations. The review result from TPA would likewise be useful for the cloud administration suppliers to upgrade cloud-based administration stage

Timed-Release Encryption With Master Time Bound Key (Full Version)

Timed-release encryption allows senders to send a message to a receiver which cannot decrypt until a server releases a time bound key at the release time. The release time usually supposed to be known to the receiver, the ciphertext therefore cannot be decrypted if the release time is lost. We solve this problem in this paper by having a master time bound key which can replace the time bound key of any release time. We first present security models of the timed-release encryption with master time bound key. We present a provably secure construction based on the Weil pairing