Papers by Zulfikar Ramzan
Lecture Notes in Computer Science, 2006
We provide algorithms to solve the free riders problem in broadcast encryption. In this problem, ... more We provide algorithms to solve the free riders problem in broadcast encryption. In this problem, the broadcast server is allowed to choose some small subset F of the revoked set R of users to allow to decrypt the broadcast, despite having been revoked. This may allow the server to significantly reduce network traffic while only allowing a small set of non-privileged users to decrypt the broadcast. Although there are worst-case instances of broadcast encryption schemes where the free riders problem is difficult to solve (or even approximate), we show that for many specific broadcast encryption schemes, there are efficient algorithms. In particular, for the complete subtree method and some other schemes in the subset-cover framework, we show how to find the optimal assignment of free riders in O(|R||F |) time, which is independent of the total number of users. We also define an approximate version of this problem, and study specific distributions of R for which this relaxation yields even faster algorithms. Along the way we develop the first approximation algorithms for the following problem: given two integer sequences a1 ≥ a2 ≥ • • • ≥ an and b1 ≥ b2 ≥ • • • ≥ bn, output for all i, an integer j for which a j + b i-j ≤ (1 + ) minj(aj + bi-j). We show that if the differences ai -ai+1, bi -bi+1 are bounded, then there is an O(n 4/3 / 2/3 )-time algorithm for this problem, improving upon the O(n 2 ) time of the naive algorithm.
Lecture Notes in Computer Science, 1998
In this paper we construct a practical group blind signature scheme. Our scheme combines the alre... more In this paper we construct a practical group blind signature scheme. Our scheme combines the already existing notions of blind signatures and group signatures. It is an extension of Camenisch and Stadler's Group Signature Scheme [5] that adds the blindness property. We show how to use our group blind signatures to construct an electronic cash system in which multiple banks can securely distribute anonymous and untraceable e-cash. Moreover, the identity of the e-cash issuing bank is concealed, which is conceptually novel. The space, time, and communication complexities of the relevant parameters and operations are independent of the group size.
Method and apparatus to secure user confidential data from untrusted browser extensions
Individualized Time-to-Live for Reputation Scores of Computer Files
Method and apparatus for retroactively detecting malicious or otherwise undesirable software
Predictive transmission of content for application streaming and network file systems
Systems and methods for authenticating requests from a client running trialware through a proof of work protocol
Application streaming and network file system optimization via integration with identity management solutions
Using Metadata In Security Tokens to Prevent Coordinated Gaming In A Reputation System
Using sequencing and timing information of behavior events in machine learning to detect malware
Method and Apparatus for Secure and Small Credits for Verifiable Service Provider Metering
Method and Apparatus for Communication Efficient Private Information Retrieval and Oblivious Transfer
Use of modular roots to perform authentication including, but not limited to, authentication of validity of digital certificates
Method and Apparatus for Efficient Certificate Revocation
Revocation of cryptographic digital certificates
Provably secure and efficient pseudorandom number generation
Lecture Notes in Computer Science, 1998
In this paper we construct a practical group blind signature scheme. Our scheme combines the alre... more In this paper we construct a practical group blind signature scheme. Our scheme combines the already existing notions of blind signatures and group signatures. It is an extension of Camenisch and Stadler's Group Signature Scheme [5] that adds the blindness property. We show how to use our group blind signatures to construct an electronic cash system in which multiple banks can securely distribute anonymous and untraceable e-cash. Moreover, the identity of the e-cash issuing bank is concealed, which is conceptually novel. The space, time, and communication complexities of the relevant parameters and operations are independent of the group size.
Lecture Notes in Computer Science, 2006
We provide algorithms to solve the free riders problem in broadcast encryption. In this problem, ... more We provide algorithms to solve the free riders problem in broadcast encryption. In this problem, the broadcast server is allowed to choose some small subset F of the revoked set R of users to allow to decrypt the broadcast, despite having been revoked. This may allow the server to significantly reduce network traffic while only allowing a small set of non-privileged users to decrypt the broadcast. Although there are worst-case instances of broadcast encryption schemes where the free riders problem is difficult to solve (or even approximate), we show that for many specific broadcast encryption schemes, there are efficient algorithms. In particular, for the complete subtree method and some other schemes in the subset-cover framework, we show how to find the optimal assignment of free riders in O(|R||F |) time, which is independent of the total number of users. We also define an approximate version of this problem, and study specific distributions of R for which this relaxation yields even faster algorithms. Along the way we develop the first approximation algorithms for the following problem: given two integer sequences a1 ≥ a2 ≥ • • • ≥ an and b1 ≥ b2 ≥ • • • ≥ bn, output for all i, an integer j for which a j + b i-j ≤ (1 + ) minj(aj + bi-j). We show that if the differences ai -ai+1, bi -bi+1 are bounded, then there is an O(n 4/3 / 2/3 )-time algorithm for this problem, improving upon the O(n 2 ) time of the naive algorithm.
Group blind signatures: A scalable solution to elec-tronic cash
Content protection in adaptive content delivery
Electronics and Communications in Japan (Part I: Communications), 2007
ABSTRACT This paper considers environment-adaptive content delivery in which an intermediary modi... more ABSTRACT This paper considers environment-adaptive content delivery in which an intermediary modifies the content between the content provider and the content user, and proposes a system in which the provider can securely control content modification by the intermediary in accordance with usage rules defined in the content. In order to have the intermediary follow the usage rules strictly, it is indispensable to provide a content protection technique in which tampering with content or usage rules by a third party is prevented while permitting content modification by intermediaries approved by the provider within the scope of the usage rules. The authors consider the hash-tree signature method in which data deletion by the intermediary is permitted, and propose a signature system with a place holder extension permitting data addition. A highly efficient realization of the proposed signature system based on the hash-sign-switch (HSS) method is presented. The effectiveness of the approach is shown by a quantitative evaluation using the implemented system. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 54–66, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20341
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Papers by Zulfikar Ramzan