title: Compression and cryptology

authors: Irvine, Sean A.

abstract: Currently data compression and encryption are carried out as two separate activities. A simpler communication system would result if these two activities could be combined. The security properties of lossless data compression techniques are investigated. It is argued that compression is necessary for security but demonstrated that current compression techniques are not sufficient. Both coding techniques (arithmetic coding and Huffman coding) and modelling techniques (splaying, Ziv-Lempel, and prediction by partial matching—PPM) are examined. It is shown that all these systems have significant security flaws. Explicit attacks are given and descriptions of algorithms to automate the attacks are provided. Chosen plaintext attacks are given for Huffman coding, PPM, and splaying. Known plaintext attacks are given for arithmetic coding, splaying and Ziv-Lempel compressors. A ciphertext only attack is given for the Ziv-Lempel compressors. These results are used to highlight why better models of natural languages have important applications in cryptology. In particular, it is explained how a better model of a source leads naturally to increased resistance from dictionary and ciphertext only attacks. 

Some of the attacks presented involve novel methods not previously reported in the literature. In particular, it is shown how a backtracking search can be used for known and chosen plaintext attacks against fixed to variable length binary encoders (Huffman coding and splaying). It is shown how a good model of the source (a PPM model) can be used in an automatic ciphertext only attack against simple substitution ciphers and Ziv-Lempel compressors. The attack against simple substitution ciphers is at least comparable to previously published automated approaches. In some cases analytical or asymptotic results concerning the complexity of the attacks are given. It appears that compression leads naturally to increased ciphertext only resistance, but current compressors contain no operations likely to thwart known or chosen plaintext attacks.

text: Compression and cryptology Currently data compression and encryption are carried out as two separate activities. A simpler communication system would result if these two activities could be combined. The security properties of lossless data compression techniques are investigated. It is argued that compression is necessary for security but demonstrated that current compression techniques are not sufficient. Both coding techniques (arithmetic coding and Huffman coding) and modelling techniques (splaying, Ziv-Lempel, and prediction by partial matching—PPM) are examined. It is shown that all these systems have significant security flaws. Explicit attacks are given and descriptions of algorithms to automate the attacks are provided. Chosen plaintext attacks are given for Huffman coding, PPM, and splaying. Known plaintext attacks are given for arithmetic coding, splaying and Ziv-Lempel compressors. A ciphertext only attack is given for the Ziv-Lempel compressors. These results are used to highlight why better models of natural languages have important applications in cryptology. In particular, it is explained how a better model of a source leads naturally to increased resistance from dictionary and ciphertext only attacks. 

Some of the attacks presented involve novel methods not previously reported in the literature. In particular, it is shown how a backtracking search can be used for known and chosen plaintext attacks against fixed to variable length binary encoders (Huffman coding and splaying). It is shown how a good model of the source (a PPM model) can be used in an automatic ciphertext only attack against simple substitution ciphers and Ziv-Lempel compressors. The attack against simple substitution ciphers is at least comparable to previously published automated approaches. In some cases analytical or asymptotic results concerning the complexity of the attacks are given. It appears that compression leads naturally to increased ciphertext only resistance, but current compressors contain no operations likely to thwart known or chosen plaintext attacks.

year: 1997

title: Some structural and photochemical studies in triterpenoids

authors: Zhu, Julie Hehui

abstract: This thesis describes the photochemical behaviour of 22-hydroxyhopan-7-one, hop-22(29)-en-7-one, 22-hydroxyhopan-15-one, hop-21-en-15-one, hop-22(29)-en-15-one, hopan-15-one and 21α-H-hopan-15-one in different solvents, and the isolation and structural elucidation of a new stictane and a new flavicane triterpene from the New Zealand lichen Pseudocyphellaria colensoi.

Photolysis of 22-hydroxyhopan-7-one in benzene-methanol was reinvestigated and confirmed to afford methyl 22-hydroxy-7,8-secohopan-7-oate. The photochemical behaviour of 22-hydroxyhopan-7-one and hop-22(29)-en-7-one in the presence of benzene alone, and in benzene-isopropanol, were also investigated.

Photolysis of hop-22(29)-en-7-one in benzene-methanol afforded methyl 7,8-secohop-22(29)en-7-oate while photolysis of 22-hydroxyhopan-7-one in methanol-isopropanol afforded isopropyl 22-hydroxy-7,8-secohopan-7-oate. Photolysis of 22-hydroxy-hopan-7-one in benzene alone afforded mainly unreacted starting material and some minor products, one of which was believed to be 22-hydroxy-7,8-secohop-8(26)-en-7-al.

The stereochemistry at C-8 for these compounds was determined by analyses of ROESY or NOESY NMR spectral data which showed the C-8 methyl group to be β-oriented, and indicated that photochemical rearrangement reactions proceeded with retention of configuration at C-8. Modelling analyses indicated the 8β-methyl secoesters to have lower energy than the corresponding 8α-methyl isomers.

Complete assignments of the ¹H and ¹³C NMR signals of methyl 22-hydroxy-7,8-secohopan-7-oate, isopropyl 22-hydroxy-7,8-secohopan-7-oate and methyl 7,8-secohop-22(29)-en-7-oate, were achieved using a combination of one- and two-dimensional NMR techniques.

The three products obtained on photolysis of 22-hydroxyhopan-15-one, in benzene-methanol, benzene-isopropanol, or benzene alone, were identified as 14,15-seco-15,22-O-abeohop-14(27)-en-15α-ol, 14,15-seco-15,22-O-abeohop-14(27)-en-15-one, and 14,15-seco-15,22-O-abeohopa-14(27), 15-diene, respectively. These products can be envisaged as arising from participation of the 22-hydroxyl group in the photoreaction pathway, after the initial formation of a 14,15-secoaldehyde.

Photolysis of hop-21-en-15-one in benzene-methanol afforded 14,15-secohopa-14(27),21-dien-15-al as the major product, while photolysis of hop-22(29)-en-15-one gave a complex mixture of products which was not further investigated. Photolysis of hopan-15-one yielded two products which were identified as the isomeric alcohols, 14,15-seco-15,22-abeohop-14(27)-en-15α-ol and 14,15-seco-15,22-abeohop-14(27)-en-15β-ol. Photolysis of 21α-H-hopan-15-one afforded two products, which were identified as methyl 14α,21α-H-14,15-secohopan-15-oate and methyl 21α-H-14,15-secohopan-15-oate.

Complete assignments of the ¹H and ¹³C NMR signals of the foregoing series of 15-oxohopanoid photoreaction products, and where appropriate the stereochemistry at C-14 and/or C-15, were achieved using a combination of one- and two-dimensional ROESY, NOESY, COSY, HMBC, and HSQC NMR spectral data, and molecular modelling results.

The results of the series of 15-oxohopanoid photoreactions can be interpreted indicating that in the presence of an α-oriented side chain (ie 22-hydroxyisopropyl group or isopropyl group) at C-21, the photoreaction proceeds with hydrogen transfer via an eight-membered transition state to afford a secoaldehyde or 14,15-secohop-4(27)-en-15-al which then affords 14,15-seco-15,22-O-abeohop-14(27)-en-15α-ol via participation of the 22-hydroxyl group and related analogues. Similarly the isomeric alcohols, 14,15-seco-15,22-abeohop-14(27)-en-15α-ol and 14,15-seco-15,22-abeohop-14(27)-en-15β-ol, obtained on photolysis of hopan-15-one can be viewed as 22-H participation products. On the other hand photolysis of a 15-oxohopanoid possessing a β-oriented side chain at C-21 was found to proceed with hydrogen transfer via a six-membered transition state to afford a pair of epimeric 14,15-secoesters.

A new stictane triterpene, and a new flavicane triterpene were isolated from extracts of the New Zealand lichen Pseudocyphellaria colensoi, and identified by analyses of mass spectral and one- and two-dimensional NMR spectral data to be 3α,6β,22α-triacetoxystictane and 22-hydroxyflavicano-25,3β-lactone, respectively. Complete assignments of the ¹H ¹³C NMR signals of the new triterpenes, and revisions to previously reported ¹³C NMR signal assignments for 22α-hydroxystictano-25,3β-lactone are reported.

text: Some structural and photochemical studies in triterpenoids This thesis describes the photochemical behaviour of 22-hydroxyhopan-7-one, hop-22(29)-en-7-one, 22-hydroxyhopan-15-one, hop-21-en-15-one, hop-22(29)-en-15-one, hopan-15-one and 21α-H-hopan-15-one in different solvents, and the isolation and structural elucidation of a new stictane and a new flavicane triterpene from the New Zealand lichen Pseudocyphellaria colensoi.

Photolysis of 22-hydroxyhopan-7-one in benzene-methanol was reinvestigated and confirmed to afford methyl 22-hydroxy-7,8-secohopan-7-oate. The photochemical behaviour of 22-hydroxyhopan-7-one and hop-22(29)-en-7-one in the presence of benzene alone, and in benzene-isopropanol, were also investigated.

Photolysis of hop-22(29)-en-7-one in benzene-methanol afforded methyl 7,8-secohop-22(29)en-7-oate while photolysis of 22-hydroxyhopan-7-one in methanol-isopropanol afforded isopropyl 22-hydroxy-7,8-secohopan-7-oate. Photolysis of 22-hydroxy-hopan-7-one in benzene alone afforded mainly unreacted starting material and some minor products, one of which was believed to be 22-hydroxy-7,8-secohop-8(26)-en-7-al.

The stereochemistry at C-8 for these compounds was determined by analyses of ROESY or NOESY NMR spectral data which showed the C-8 methyl group to be β-oriented, and indicated that photochemical rearrangement reactions proceeded with retention of configuration at C-8. Modelling analyses indicated the 8β-methyl secoesters to have lower energy than the corresponding 8α-methyl isomers.

Complete assignments of the ¹H and ¹³C NMR signals of methyl 22-hydroxy-7,8-secohopan-7-oate, isopropyl 22-hydroxy-7,8-secohopan-7-oate and methyl 7,8-secohop-22(29)-en-7-oate, were achieved using a combination of one- and two-dimensional NMR techniques.

The three products obtained on photolysis of 22-hydroxyhopan-15-one, in benzene-methanol, benzene-isopropanol, or benzene alone, were identified as 14,15-seco-15,22-O-abeohop-14(27)-en-15α-ol, 14,15-seco-15,22-O-abeohop-14(27)-en-15-one, and 14,15-seco-15,22-O-abeohopa-14(27), 15-diene, respectively. These products can be envisaged as arising from participation of the 22-hydroxyl group in the photoreaction pathway, after the initial formation of a 14,15-secoaldehyde.

Photolysis of hop-21-en-15-one in benzene-methanol afforded 14,15-secohopa-14(27),21-dien-15-al as the major product, while photolysis of hop-22(29)-en-15-one gave a complex mixture of products which was not further investigated. Photolysis of hopan-15-one yielded two products which were identified as the isomeric alcohols, 14,15-seco-15,22-abeohop-14(27)-en-15α-ol and 14,15-seco-15,22-abeohop-14(27)-en-15β-ol. Photolysis of 21α-H-hopan-15-one afforded two products, which were identified as methyl 14α,21α-H-14,15-secohopan-15-oate and methyl 21α-H-14,15-secohopan-15-oate.

Complete assignments of the ¹H and ¹³C NMR signals of the foregoing series of 15-oxohopanoid photoreaction products, and where appropriate the stereochemistry at C-14 and/or C-15, were achieved using a combination of one- and two-dimensional ROESY, NOESY, COSY, HMBC, and HSQC NMR spectral data, and molecular modelling results.

The results of the series of 15-oxohopanoid photoreactions can be interpreted indicating that in the presence of an α-oriented side chain (ie 22-hydroxyisopropyl group or isopropyl group) at C-21, the photoreaction proceeds with hydrogen transfer via an eight-membered transition state to afford a secoaldehyde or 14,15-secohop-4(27)-en-15-al which then affords 14,15-seco-15,22-O-abeohop-14(27)-en-15α-ol via participation of the 22-hydroxyl group and related analogues. Similarly the isomeric alcohols, 14,15-seco-15,22-abeohop-14(27)-en-15α-ol and 14,15-seco-15,22-abeohop-14(27)-en-15β-ol, obtained on photolysis of hopan-15-one can be viewed as 22-H participation products. On the other hand photolysis of a 15-oxohopanoid possessing a β-oriented side chain at C-21 was found to proceed with hydrogen transfer via a six-membered transition state to afford a pair of epimeric 14,15-secoesters.

A new stictane triterpene, and a new flavicane triterpene were isolated from extracts of the New Zealand lichen Pseudocyphellaria colensoi, and identified by analyses of mass spectral and one- and two-dimensional NMR spectral data to be 3α,6β,22α-triacetoxystictane and 22-hydroxyflavicano-25,3β-lactone, respectively. Complete assignments of the ¹H ¹³C NMR signals of the new triterpenes, and revisions to previously reported ¹³C NMR signal assignments for 22α-hydroxystictano-25,3β-lactone are reported.

year: 2000

title: Toi tu te whenua, toi tu te tangata: A holistic Māori approach to flood management in Pawarenga

authors: Proctor, Elizabeth-Mary

subjects: flood management

abstract: This thesis is a study of how tikanga Māori principles could be used in practice in the management of natural hazards and in particular flooding in a rural area, Pawarenga. The aim was to investigate and document Te Uri O Tai Hapū preferred strategies for reducing flood risk in Pawarenga and to consider opportunities to use tikanga Māori principles and values in emergency response. The identification of key concepts and principles of tikanga Māori customs and their connections to whānau and hapū of Te Uri O Tai is key to this study. I used kaupapa Māori research methodologies as a guiding framework since researching in my own community required me to manage accountability both to its members and to the university. In particular it was important to obtain permission from the community before beginning, to ensure my research processes were acceptable, and to return my findings to the community. Qualitative data was gathered from a series of hui and interviews with local community members. Data was analysed inductively and organised into thematic networks. Two major organising themes were identified: resilience and vulnerability. Participants described a broad range of strengths inherent in the community that enabled them to respond to crises such as flood events. A number of cultural, social, physical, economic and political vulnerabilities were also identified; most of these were fundamental aspects of people‘s daily lives and did not prevent them from responding positively when floods occurred, but may have limited the scope of their responses. Tikanga was not a subject that participants felt comfortable talking about, but from the descriptions of how people actually responded during floods I was able to see examples of how tikanga was used. The resilience of the Pawarenga community is taken for granted by residents. When disasters such as floods occur, their resiliencies and strengths are brought into play to ensure the safety of all in the community. Tikanga Māori is an inherent part of this resiliency, and marae structures and protocols already in place provide a vital framework for flood response. I conclude that tikanga already has enormous value in flood response, and for Māori communities is an obvious choice as a foundation for a flood emergency management strategy. Furthermore, the value of tikanga as a flood emergency management strategy should be more explicitly recognised and supported by all authorities involved in disaster response and management. It was also clear that multiple dimensions of vulnerability (physical, cultural, social, economic and political) affect the Pawarenga community, and to some extent limit their capacity to respond. In particular political processes that exclude them from participating in decision-making and planning around environmental management generally have left people feeling marginalised, since they are unable to fulfil their kaitiaki role. With civil defence emergency management policies explicitly focused around resilience, participation of Te Uri O Tai Hapū in planning for emergency management should allow for their existing resilience, which stems from the upholding of tikanga, to be recognised and strengthened. However, this will only happen if relationships with the various authorities involved in emergency and natural hazard response are fostered, full participation in decision-making and in responding to natural hazard events is facilitated, and resources are available to support the community with their endeavours.

text: Toi tu te whenua, toi tu te tangata: A holistic Māori approach to flood management in Pawarenga This thesis is a study of how tikanga Māori principles could be used in practice in the management of natural hazards and in particular flooding in a rural area, Pawarenga. The aim was to investigate and document Te Uri O Tai Hapū preferred strategies for reducing flood risk in Pawarenga and to consider opportunities to use tikanga Māori principles and values in emergency response. The identification of key concepts and principles of tikanga Māori customs and their connections to whānau and hapū of Te Uri O Tai is key to this study. I used kaupapa Māori research methodologies as a guiding framework since researching in my own community required me to manage accountability both to its members and to the university. In particular it was important to obtain permission from the community before beginning, to ensure my research processes were acceptable, and to return my findings to the community. Qualitative data was gathered from a series of hui and interviews with local community members. Data was analysed inductively and organised into thematic networks. Two major organising themes were identified: resilience and vulnerability. Participants described a broad range of strengths inherent in the community that enabled them to respond to crises such as flood events. A number of cultural, social, physical, economic and political vulnerabilities were also identified; most of these were fundamental aspects of people‘s daily lives and did not prevent them from responding positively when floods occurred, but may have limited the scope of their responses. Tikanga was not a subject that participants felt comfortable talking about, but from the descriptions of how people actually responded during floods I was able to see examples of how tikanga was used. The resilience of the Pawarenga community is taken for granted by residents. When disasters such as floods occur, their resiliencies and strengths are brought into play to ensure the safety of all in the community. Tikanga Māori is an inherent part of this resiliency, and marae structures and protocols already in place provide a vital framework for flood response. I conclude that tikanga already has enormous value in flood response, and for Māori communities is an obvious choice as a foundation for a flood emergency management strategy. Furthermore, the value of tikanga as a flood emergency management strategy should be more explicitly recognised and supported by all authorities involved in disaster response and management. It was also clear that multiple dimensions of vulnerability (physical, cultural, social, economic and political) affect the Pawarenga community, and to some extent limit their capacity to respond. In particular political processes that exclude them from participating in decision-making and planning around environmental management generally have left people feeling marginalised, since they are unable to fulfil their kaitiaki role. With civil defence emergency management policies explicitly focused around resilience, participation of Te Uri O Tai Hapū in planning for emergency management should allow for their existing resilience, which stems from the upholding of tikanga, to be recognised and strengthened. However, this will only happen if relationships with the various authorities involved in emergency and natural hazard response are fostered, full participation in decision-making and in responding to natural hazard events is facilitated, and resources are available to support the community with their endeavours.

year: 2010