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Adaptive homophonic coding techniques for enhanced e-commerce security
Dissertation (MEng (Data Security))--University of Pretoria, 2002.
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| Format: | Thesis |
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University of Pretoria
2013
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| _version_ | 1867613669138890752 |
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| access_status_str | Open Access |
| author2 | Penzhorn, W.T. |
| author_browse | Penzhorn, W.T. |
| author_facet | Penzhorn, W.T. |
| collection | Thesis |
| dc_rights_str_mv | © 2002, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Dissertation (MEng (Data Security))--University of Pretoria, 2002. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/27663 |
| institution | University of Pretoria (South Africa) |
| last_indexed | 2026-06-10T12:39:48.717Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2013 |
| publishDateRange | 2013 |
| publishDateSort | 2013 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/27663 Adaptive homophonic coding techniques for enhanced e-commerce security Penzhorn, W.T. upetd@up.ac.za Kruger, David Computer security Electronic commerce UCTD Dissertation (MEng (Data Security))--University of Pretoria, 2002. This dissertation considers a method to convert an ordinary cipher system, as used to secure e-commerce transactions, into an unconditionally secure cipher system, i.e. one that generates ciphertext that does not contain enough statistical information to break the cipher, irrespective of how much ciphertext is available. Shannon showed that this can be achieved by maximizing the entropy of the message sequence to be encrypted. This, in turn, achieved by means of homophonic coding. Homophonic coding substitutes characters in the message source with randomly chosen codewords. It offers the advantage that it enables protection against known- and chosen plaintext attacks on cipher algorithms since source statistics are randomly changed before encryption. The disadvantage of homophonic substitution is that it will in general increase the length of the message sequence. To compensate for this, homophonic coding is combined with the data compression algorithm known as arithmetic coding. It is shown that the arithmetic coding algorithm can be adapted to perform homophonic coding by dyadically decomposing the character probabilities in its probability estimation phase. By doing this, a faster version of arithmetic coding, known as shift-and-add arithmetic coding can be implemented. A new method of statistical modelling, based on an Infinite Impulse Response filtering method is presented. A method to adapt the well-known Lempel-Ziv- Welch compression algorithm to perform homophonic coding is also presented. The procedure involves a bit-wise exclusive-or randomization operation during encoding. The results show that the adapted algorithms do indeed increase the entropy of the source sequences by no more than 2 bits/symbol, and even offers compression in some cases. Electrical, Electronic and Computer Engineering unrestricted 2013-09-07T11:57:37Z 2005-09-05 2013-09-07T11:57:37Z 2002-10-09 2002 2005-09-01 Dissertation Kruger, D 2002, Adaptive homophonic coding techniques for enhanced e-commerce security, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://hdl.handle.net/2263/27663 > H621/ag http://hdl.handle.net/2263/27663 http://upetd.up.ac.za/thesis/available/etd-09012005-115040/ © 2002, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | Computer security Electronic commerce UCTD Adaptive homophonic coding techniques for enhanced e-commerce security |
| title | Adaptive homophonic coding techniques for enhanced e-commerce security |
| title_full | Adaptive homophonic coding techniques for enhanced e-commerce security |
| title_fullStr | Adaptive homophonic coding techniques for enhanced e-commerce security |
| title_full_unstemmed | Adaptive homophonic coding techniques for enhanced e-commerce security |
| title_short | Adaptive homophonic coding techniques for enhanced e-commerce security |
| title_sort | adaptive homophonic coding techniques for enhanced e commerce security |
| topic | Computer security Electronic commerce UCTD |
| url | http://hdl.handle.net/2263/27663 http://upetd.up.ac.za/thesis/available/etd-09012005-115040/ |