| 1. |
- Anderson, Kristin, 1977-, et al.
(author)
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Broadcast Encryption and Group Codes
- 2004
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Reports (other academic/artistic)abstract
- We consider the subset difference scheme for broadcast encryption and count the number of required transmissions when using this scheme. The subset scheme organizes receivers in a tree structure and we note that isomorphic trees yield the same number of required transmissions. We then study the group properties of isomorphism classes of trees. Finally we formulate some research questions for further study of the performance of the subset difference scheme.
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| 2. |
- Anderson, Kristin, 1977-
(author)
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Cost-Distortion Measures for Broadcast Encryption
- 2005
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In: NordSec 2005. Student session,2005.
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Conference paper (other academic/artistic)abstract
- In a typical broadcast encryption scenario, a sender wishes to securely transmit messages to a subset of receivers, the intended set, using a broadcast channel. Several schemes for broadcast encryption exist and they allow the sender to reach a privileged set of receivers and by the use of encryption block all others from receiving the message. Most of the existing broadcast encryption literature assumes that the intended set and the privileged set are equal but this is not always necessary. In some applications a slight difference between the intended and the privileged set may be tolerated if the cost of transmitting the message decreases sufficiently. It has been suggested that a few free-riders, users not in the intended set but in the privileged set, may be allowed in some scenarios. In rare cases the opposite could also be possible, that is some users are in the intended set but not in the privileged set. Our approach is to use the information theoretic concept of distortion to measure the discrepancy between the intended and the privileged sets. As a cost measure we use the average number of transmissions required to send one message. As an example of the use for these measures we have developed three simple algorithms that aim to lower the cost by adding some distortion; one greedy algorithm and two versions of an algorithm based on randomness. By simulations we have compared them using our cost and distortion measures. The subset difference (SD) scheme has been used as the underlying broadcast encryption scheme. The greedy algorithm is not tightly bound to the SD scheme while the two randomness-based algorithms take some use of the properties of the SD scheme.
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| 3. |
- Anderson, Kristin, 1977-, et al.
(author)
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Effects of User Adjacency in the Subset Difference Scheme for Broadcast Encryption
- 2005
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In: Radiovetenskap och Kommunikation, RVK05,2005.
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Conference paper (peer-reviewed)abstract
- We consider the broadcast encryption problem where one sender wishes to transmit messages securely to a selected set of receivers using a broadcast channel, as is the case in digital television for example. Specifically, we study the subset difference scheme for broadcast encryption and the number of broadcast transmissions required when using this scheme. The effects of adjacency in the user set are considered and we introduce the notion of transitions in the user set as a means to quantify the adjacency. We present upper and lower bounds for the number of transmissions based on the number of transitions between privileged and nonprivileged users in the user set. For cases where the privileged users are gathered in a few groups we derive the maximum number of transmissions.
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| 4. |
- Anderson, Kristin, 1977-
(author)
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Performance of the Subset Difference Scheme for Broadcast Encryption
- 2004
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Reports (other academic/artistic)abstract
- This report considers the subset difference scheme for broadcast encryption and the number of broadcast transmissions required when using this scheme. For cases where the privileged users are gathered in a few groups we derive the worst case number of transmissions. We also present an upper bound for the number of transmissions based on the number of transitions between privileged and nonprivileged users in the user set.
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| 5. |
- Anderson, Kristin, 1977-, et al.
(author)
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The Algebraic Structure of a Broadcast Encryption Scheme
- 2005
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In: Radiovetenskap och Kommunikation, RVK05,2005.
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Conference paper (peer-reviewed)abstract
- In this paper we consider the subset difference scheme for broadcast encryption and count the number of required broadcast transmissions when using this scheme. The subset difference scheme organizes receivers in a tree structure and we note that isomorphic trees yield the same number of required broadcast transmissions. Based on the isomorphism the trees can be partitioned into classes. We suggest to use the vast amount of tools available from the theory of groups to analyze the subset difference scheme and therefore we formulate the mappings between isomorphic trees using concepts from group theory. Finally we identify some research issues for further study of the performance of the subset difference scheme using group theory.
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| 6. |
- Anderson, Kristin, 1977-
(author)
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Tree Structures in Broadcast Encryption
- 2005
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Licentiate thesis (other academic/artistic)abstract
- The need for broadcast encryption arises when a sender wishes to securely distribute messages to varying subsets of receivers, using a broadcast channel, for instance in a pay-TV scenario. This is done by selecting subsets of users and giving all users in the same subset a common decryption key. The subsets will in general be overlapping so that each user belongs to many subsets and has several different decryption keys. When the sender wants to send a message to some users, the message is encrypted using keys that those users have. In this thesis we describe some broadcast encryption schemes that have been proposed in the literature. We focus on stateless schemes which do not require receivers to update their decryption keys after the initial keys have been received; particularly we concentrate on the Subset Difference (SD) scheme.We consider the effects that the logical placement of the receivers in the tree structure used by the SD scheme has on the number of required transmissions for each message. Bounds for the number of required transmissions are derived based on the adjacency of receivers in the tree structure. The tree structure itself is also studied, also resulting in bounds on the number of required transmissions based on the placement of the users in the tree structure.By allowing a slight discrepancy between the set of receivers that the sender intends to send to and the set of receivers that actually can decrypt the message, we can reduce the cost in number of transmissions per message. We use the concept of distortion to quantify the discrepancy and develop three simple algorithms to illustrate how the cost and distortion are related.
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