[{"title":"On secure chain selection rules from physical resources in a permissionless setting","doi":"10.15479/AT-ISTA-21651","oa_version":"Published Version","corr_author":"1","status":"public","abstract":[{"lang":"eng","text":"Blockchains enable distributed consensus in permissionless settings, where participants\r\nare unknown, dynamically changing, and do not trust each other. While Bitcoin,\r\nbased on Proof-of-Work (PoW), was the first protocol in this model, significant\r\nresearch has focused on permissionless protocols using alternative physical resources,\r\nspecifically Proof-of-Space (PoSpace) and Verifiable Delay Functions (VDFs). This\r\nthesis investigates the theoretical limits and design space of longest-chain protocols in\r\nthe fully permissionless and dynamically available settings using these three resources.\r\nFirst, we address the feasibility of blockchains relying solely on storage as a resource.\r\nWe prove a fundamental impossibility result: there exists no secure longest-chain\r\nprotocol based exclusively on Proof-of-Space in the fully permissionless or dynamically\r\navailable settings. Further, we quantify the adversarial capabilities required to execute\r\na double-spend attack. Our result formally justifies the necessity of coupling PoSpace\r\nwith time-dependent primitives (such as VDFs) or to move to less permissive settings\r\n(quasi-permissionless or permissioned) to ensure security.\r\nSecond, we generalize Nakamoto-like heaviest chain consensus to protocols utilizing\r\ncombinations of multiple physical resources. We analyze chain selection rules governed\r\nby a weight function Γ(S, V,W), which assigns weight to blocks based on recorded\r\nSpace (S), VDF speed (V ), and Work (W). We provide a complete classification\r\nof secure weight functions, proving that a weight function is secure against private\r\ndouble-spend attacks if and only if it is homogeneous in the timed resources (V,W)\r\nand sub-homogeneous in S. This framework unifies existing protocols like Bitcoin and\r\nChia under a single theoretical model and provides a powerful tool for designing new\r\nlongest-chain blockchains from a mix of physical resources."}],"OA_place":"publisher","publication_status":"published","year":"2026","file":[{"file_name":"PhD-Thesis-Mirza-Ahad-Baig - Library Submission.zip","relation":"source_file","creator":"mbaig","checksum":"c3986dba90653dac97adba662ebff238","access_level":"closed","file_size":139353434,"file_id":"21655","date_created":"2026-04-03T17:28:48Z","content_type":"application/x-zip-compressed","date_updated":"2026-04-13T08:24:13Z"},{"file_name":"2026_Baig_Mirza_Ahad_Thesis.pdf","creator":"mbaig","relation":"main_file","file_id":"21656","file_size":1942037,"access_level":"open_access","checksum":"292a5989262521f7c145a109d1f348cb","content_type":"application/pdf","date_updated":"2026-04-15T07:37:25Z","date_created":"2026-04-03T17:29:30Z"}],"day":"04","article_processing_charge":"No","author":[{"id":"3EDE6DE4-AA5A-11E9-986D-341CE6697425","full_name":"Baig, Mirza Ahad","first_name":"Mirza Ahad","last_name":"Baig"}],"publisher":"Institute of Science and Technology Austria","date_published":"2026-03-04T00:00:00Z","degree_awarded":"PhD","publication_identifier":{"issn":["2663-337X"],"isbn":["978-3-99078-078-7"]},"_id":"21651","department":[{"_id":"GradSch"},{"_id":"KrPi"}],"has_accepted_license":"1","license":"https://creativecommons.org/licenses/by-nc-sa/4.0/","alternative_title":["ISTA Thesis"],"language":[{"iso":"eng"}],"tmp":{"short":"CC BY-NC-SA (4.0)","legal_code_url":"https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode","name":"Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)","image":"/images/cc_by_nc_sa.png"},"supervisor":[{"full_name":"Pietrzak, Krzysztof Z","first_name":"Krzysztof Z","id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87","orcid":"0000-0002-9139-1654","last_name":"Pietrzak"}],"ddc":["000"],"month":"03","type":"dissertation","citation":{"chicago":"Baig, Mirza Ahad. “On Secure Chain Selection Rules from Physical Resources in a Permissionless Setting.” Institute of Science and Technology Austria, 2026. <a href=\"https://doi.org/10.15479/AT-ISTA-21651\">https://doi.org/10.15479/AT-ISTA-21651</a>.","apa":"Baig, M. A. (2026). <i>On secure chain selection rules from physical resources in a permissionless setting</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/AT-ISTA-21651\">https://doi.org/10.15479/AT-ISTA-21651</a>","mla":"Baig, Mirza Ahad. <i>On Secure Chain Selection Rules from Physical Resources in a Permissionless Setting</i>. Institute of Science and Technology Austria, 2026, doi:<a href=\"https://doi.org/10.15479/AT-ISTA-21651\">10.15479/AT-ISTA-21651</a>.","ista":"Baig MA. 2026. On secure chain selection rules from physical resources in a permissionless setting. Institute of Science and Technology Austria.","short":"M.A. Baig, On Secure Chain Selection Rules from Physical Resources in a Permissionless Setting, Institute of Science and Technology Austria, 2026.","ama":"Baig MA. On secure chain selection rules from physical resources in a permissionless setting. 2026. doi:<a href=\"https://doi.org/10.15479/AT-ISTA-21651\">10.15479/AT-ISTA-21651</a>","ieee":"M. A. Baig, “On secure chain selection rules from physical resources in a permissionless setting,” Institute of Science and Technology Austria, 2026."},"date_created":"2026-04-02T09:31:34Z","file_date_updated":"2026-04-15T07:37:25Z","date_updated":"2026-04-15T08:45:19Z","oa":1,"related_material":{"record":[{"status":"public","id":"21134","relation":"part_of_dissertation"},{"status":"public","relation":"part_of_dissertation","id":"20587"}]},"user_id":"8b945eb4-e2f2-11eb-945a-df72226e66a9"},{"oa_version":"Published Version","doi":"10.15479/AT-ISTA-20920","title":"Theory and applications of verifiable delay functions","date_published":"2025-12-31T00:00:00Z","author":[{"last_name":"Hoffmann","orcid":"0000-0003-2027-5549","id":"0f78d746-dc7d-11ea-9b2f-83f92091afe7","first_name":"Charlotte","full_name":"Hoffmann, Charlotte"}],"publisher":"Institute of Science and Technology Austria","article_processing_charge":"No","day":"31","file":[{"file_name":"2025_Hoffmann_Charlotte_Source.zip","relation":"source_file","creator":"choffman","checksum":"8a099fbf54963bd0be38f7ce73658682","access_level":"closed","file_size":8355494,"file_id":"20921","date_created":"2026-01-02T10:39:16Z","date_updated":"2026-01-02T10:39:16Z","content_type":"application/x-zip-compressed"},{"file_id":"20922","file_size":2258804,"access_level":"open_access","checksum":"9521c07bfb2bb5b14a49c09fcfc96474","success":1,"content_type":"application/pdf","date_updated":"2026-01-02T10:39:26Z","date_created":"2026-01-02T10:39:26Z","file_name":"2025_Hoffmann_Charlotte_Thesis.pdf","creator":"choffman","relation":"main_file"}],"year":"2025","abstract":[{"lang":"eng","text":"Verifiable Delay Functions (VDFs) introduced by Boneh et al. (CRYPTO'18) are functions that require a prescribed number of sequential steps T to evaluate, yet their output can be verified in time much faster than T. Since their introduction, VDFs have gained a lot of attention due to their applications in blockchain protocols, randomness beacons, timestamping and deniability. This thesis explores the theory and applications of VDFs, focusing on enhancing their soundness, efficiency and practicality.\r\n\r\nThe only practical VDFs known to date are based on repeated squaring in hidden order groups. Consider the function VDF(x,T)=x^(2^T).\r\nThe iterated squaring assumption states that, for a random group element x, the result of VDF cannot be computed significantly faster than performing T sequential squarings if the group order is unknown. To make the result verifiable a prover can compute a proof of exponentiation (PoE) \\pi. Given \\pi, the output of VDF can be verified in time much less than T.\r\n\r\nWe first present new constructions of statistically sound proofs of exponentiation, which are an important building block in the construction of SNARKs (Succinct Non-Interactive Argument of Knowledge). Statistical soundness means that the proofs remain secure against computationally unbounded adversaries, in particular, it remains secure even when the group order is known. We thereby address limitations in previous PoE protocols which either required (non-standard) hardness assumptions or a lot of parallel repetitions. Our construction significantly reduces the proof size of statistically sound PoEs that allow for a structured exponent, which leads to better efficiency of SNARKs and other applications.\r\n\r\nSecondly, we introduce improved batching techniques for PoEs, which allow multiple proofs to be aggregated and verified with minimal overhead. These protocols optimize communication and computation complexity in large-scale blockchain environments and enable scalable remote benchmarking of parallel computation resources.\r\n\r\nWe then construct VDFs with enhanced properties such as zero-knowledge and watermarkability. It was shown by Arun, Bonneau and Clark (ASIACRYPT'22) that these features enable new cryptographic primitives called short-lived proofs and signatures. The validity of such proofs and signatures expires after a predefined amount of time T, i.e., they are deniable after time T. Our constructions improve upon the constructions by Arun, Bonneau and Clark in several dimensions (faster forging times, arguably weaker assumptions).\r\n\r\nFinally, we apply PoEs in the realm of primality testing, providing cryptographically sound proofs of non-primality for large Proth numbers. This work gives a surprising application of VDFs in the area of computational number theory.\r\n\r\nTogether, our contributions advance both the theoretical foundations and the real-world usability of VDFs in general and in particular of PoEs, making them more adaptable and secure for current and emerging cryptographic applications."}],"publication_status":"published","OA_place":"publisher","status":"public","corr_author":"1","month":"12","ddc":["004"],"supervisor":[{"orcid":"0000-0002-9139-1654","id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87","first_name":"Krzysztof Z","full_name":"Pietrzak, Krzysztof Z","last_name":"Pietrzak"}],"tmp":{"short":"CC BY-NC-SA (4.0)","legal_code_url":"https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode","name":"Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)","image":"/images/cc_by_nc_sa.png"},"language":[{"iso":"eng"}],"alternative_title":["ISTA Thesis"],"has_accepted_license":"1","page":"116","_id":"20920","department":[{"_id":"GradSch"},{"_id":"KrPi"}],"publication_identifier":{"issn":["2663-337X"]},"degree_awarded":"PhD","user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","related_material":{"record":[{"id":"13143","relation":"part_of_dissertation","status":"public"},{"status":"public","id":"20701","relation":"part_of_dissertation"},{"status":"public","relation":"part_of_dissertation","id":"12176"},{"id":"20556","relation":"earlier_version","status":"public"},{"id":"19778","relation":"part_of_dissertation","status":"public"}]},"oa":1,"date_updated":"2026-04-16T09:11:08Z","file_date_updated":"2026-01-02T10:39:26Z","date_created":"2026-01-02T10:46:47Z","type":"dissertation","citation":{"ieee":"C. Hoffmann, “Theory and applications of verifiable delay functions,” Institute of Science and Technology Austria, 2025.","ista":"Hoffmann C. 2025. Theory and applications of verifiable delay functions. Institute of Science and Technology Austria.","ama":"Hoffmann C. Theory and applications of verifiable delay functions. 2025. doi:<a href=\"https://doi.org/10.15479/AT-ISTA-20920\">10.15479/AT-ISTA-20920</a>","short":"C. Hoffmann, Theory and Applications of Verifiable Delay Functions, Institute of Science and Technology Austria, 2025.","mla":"Hoffmann, Charlotte. <i>Theory and Applications of Verifiable Delay Functions</i>. Institute of Science and Technology Austria, 2025, doi:<a href=\"https://doi.org/10.15479/AT-ISTA-20920\">10.15479/AT-ISTA-20920</a>.","chicago":"Hoffmann, Charlotte. “Theory and Applications of Verifiable Delay Functions.” Institute of Science and Technology Austria, 2025. <a href=\"https://doi.org/10.15479/AT-ISTA-20920\">https://doi.org/10.15479/AT-ISTA-20920</a>.","apa":"Hoffmann, C. (2025). <i>Theory and applications of verifiable delay functions</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/AT-ISTA-20920\">https://doi.org/10.15479/AT-ISTA-20920</a>"}},{"file":[{"relation":"main_file","creator":"choffman","file_name":"2025_Hoffmann_Charlotte_Thesis.pdf","date_created":"2025-10-28T14:33:03Z","date_updated":"2026-01-08T14:11:39Z","content_type":"application/pdf","access_level":"closed","checksum":"1fffa4e2c33dd0b9f883d615504a2858","file_id":"20573","file_size":2259304},{"checksum":"076ea98a1f0a86c3bbc990b6b9460dc2","access_level":"closed","file_size":9987633,"file_id":"20574","date_created":"2025-10-28T14:35:06Z","date_updated":"2025-11-11T09:34:54Z","content_type":"application/x-zip-compressed","file_name":"2025_Hoffmann_Charlotte_Source.zip","relation":"source_file","creator":"choffman"}],"article_processing_charge":"No","day":"31","author":[{"last_name":"Hoffmann","orcid":"0000-0003-2027-5549","id":"0f78d746-dc7d-11ea-9b2f-83f92091afe7","first_name":"Charlotte","full_name":"Hoffmann, Charlotte"}],"publisher":"Institute of Science and Technology Austria","date_published":"2025-10-31T00:00:00Z","status":"public","corr_author":"1","OA_place":"publisher","publication_status":"published","abstract":[{"text":"Verifiable Delay Functions (VDFs) introduced by Boneh et al. (CRYPTO'18) are functions that require a prescribed number of sequential steps T to evaluate, yet their output can be verified in time much faster than T. Since their introduction, VDFs have gained a lot of attention due to their applications in blockchain protocols, randomness beacons, timestamping and deniability. This thesis explores the theory and applications of VDFs, focusing on enhancing their soundness, efficiency and practicality.\r\n\r\nThe only practical VDFs known to date are based on repeated squaring in hidden order groups. Consider the function VDF(x,T)=x^(2^T).\r\nThe iterated squaring assumption states that, for a random group element x, the result of VDF cannot be computed significantly faster than performing T sequential squarings if the group order is unknown. To make the result verifiable a prover can compute a proof of exponentiation (PoE) \\pi. Given \\pi, the output of VDF can be verified in time much less than T.\r\n\r\nWe first present new constructions of statistically sound proofs of exponentiation, which are an important building block in the construction of SNARKs (Succinct Non-Interactive Argument of Knowledge). Statistical soundness means that the proofs remain secure against computationally unbounded adversaries, in particular, it remains secure even when the group order is known. We thereby address limitations in previous PoE protocols which either required (non-standard) hardness assumptions or a lot of parallel repetitions. Our construction significantly reduces the proof size of statistically sound PoEs that allow for a structured exponent, which leads to better efficiency of SNARKs and other applications.\r\n\r\nSecondly, we introduce improved batching techniques for PoEs, which allow multiple proofs to be aggregated and verified with minimal overhead. These protocols optimize communication and computation complexity in large-scale blockchain environments and enable scalable remote benchmarking of parallel computation resources.\r\n\r\nWe then construct VDFs with enhanced properties such as zero-knowledge and watermarkability. It was shown by Arun, Bonneau and Clark (ASIACRYPT'22) that these features enable new cryptographic primitives called short-lived proofs and signatures. The validity of such proofs and signatures expires after a predefined amount of time T, i.e., they are deniable after time T. Our constructions improve upon the constructions by Arun, Bonneau and Clark in several dimensions (faster forging times, arguably weaker assumptions).\r\n\r\nFinally, we apply PoEs in the realm of primality testing, providing cryptographically sound proofs of non-primality for large Proth numbers. This work gives a surprising application of VDFs in the area of computational number theory.\r\n\r\nTogether, our contributions advance both the theoretical foundations and the real-world usability of VDFs in general and in particular of PoEs, making them more adaptable and secure for current and emerging cryptographic applications.","lang":"eng"}],"year":"2025","doi":"10.15479/AT-ISTA-20556","title":"Theory and applications of verifiable delay functions","oa_version":"Published Version","related_material":{"record":[{"status":"public","relation":"part_of_dissertation","id":"13143"},{"status":"public","id":"12176","relation":"part_of_dissertation"},{"status":"public","id":"20701","relation":"part_of_dissertation"},{"status":"public","id":"20920","relation":"later_version"},{"status":"public","relation":"part_of_dissertation","id":"19778"}]},"user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","citation":{"apa":"Hoffmann, C. (2025). <i>Theory and applications of verifiable delay functions</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/AT-ISTA-20556\">https://doi.org/10.15479/AT-ISTA-20556</a>","chicago":"Hoffmann, Charlotte. “Theory and Applications of Verifiable Delay Functions.” Institute of Science and Technology Austria, 2025. <a href=\"https://doi.org/10.15479/AT-ISTA-20556\">https://doi.org/10.15479/AT-ISTA-20556</a>.","mla":"Hoffmann, Charlotte. <i>Theory and Applications of Verifiable Delay Functions</i>. Institute of Science and Technology Austria, 2025, doi:<a href=\"https://doi.org/10.15479/AT-ISTA-20556\">10.15479/AT-ISTA-20556</a>.","short":"C. Hoffmann, Theory and Applications of Verifiable Delay Functions, Institute of Science and Technology Austria, 2025.","ama":"Hoffmann C. Theory and applications of verifiable delay functions. 2025. doi:<a href=\"https://doi.org/10.15479/AT-ISTA-20556\">10.15479/AT-ISTA-20556</a>","ista":"Hoffmann C. 2025. Theory and applications of verifiable delay functions. Institute of Science and Technology Austria.","ieee":"C. Hoffmann, “Theory and applications of verifiable delay functions,” Institute of Science and Technology Austria, 2025."},"type":"dissertation","date_created":"2025-10-27T14:16:56Z","date_updated":"2026-04-16T09:11:09Z","file_date_updated":"2026-01-08T14:11:39Z","language":[{"iso":"eng"}],"supervisor":[{"last_name":"Pietrzak","first_name":"Krzysztof Z","full_name":"Pietrzak, Krzysztof Z","orcid":"0000-0002-9139-1654","id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87"}],"tmp":{"short":"CC BY-NC-SA (4.0)","legal_code_url":"https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode","name":"Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)","image":"/images/cc_by_nc_sa.png"},"ddc":["004"],"month":"10","degree_awarded":"PhD","publication_identifier":{"issn":["2663-337X"]},"_id":"20556","department":[{"_id":"GradSch"},{"_id":"KrPi"}],"alternative_title":["ISTA Thesis"],"page":"116","has_accepted_license":"1"},{"ddc":["000"],"month":"09","language":[{"iso":"eng"}],"supervisor":[{"orcid":"0000-0002-9139-1654","id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87","first_name":"Krzysztof Z","full_name":"Pietrzak, Krzysztof Z","last_name":"Pietrzak"}],"tmp":{"short":"CC BY-NC-SA (4.0)","legal_code_url":"https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode","name":"Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)","image":"/images/cc_by_nc_sa.png"},"department":[{"_id":"KrPi"},{"_id":"GradSch"}],"_id":"18088","alternative_title":["ISTA Thesis"],"page":"239","has_accepted_license":"1","degree_awarded":"PhD","publication_identifier":{"issn":["2663-337X"]},"related_material":{"record":[{"status":"public","id":"10408","relation":"part_of_dissertation"},{"status":"public","relation":"part_of_dissertation","id":"11476"},{"id":"18086","relation":"part_of_dissertation","status":"public"},{"relation":"part_of_dissertation","id":"10049","status":"public"}]},"user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","oa":1,"date_created":"2024-09-18T12:59:49Z","date_updated":"2026-04-07T13:01:26Z","file_date_updated":"2024-09-19T12:36:08Z","citation":{"mla":"Pascual Perez, Guillermo. <i>On the Efficiency and Security of Secure Group Messaging</i>. Institute of Science and Technology Austria, 2024, doi:<a href=\"https://doi.org/10.15479/at:ista:18088\">10.15479/at:ista:18088</a>.","apa":"Pascual Perez, G. (2024). <i>On the efficiency and security of secure group messaging</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/at:ista:18088\">https://doi.org/10.15479/at:ista:18088</a>","chicago":"Pascual Perez, Guillermo. “On the Efficiency and Security of Secure Group Messaging.” Institute of Science and Technology Austria, 2024. <a href=\"https://doi.org/10.15479/at:ista:18088\">https://doi.org/10.15479/at:ista:18088</a>.","ieee":"G. Pascual Perez, “On the efficiency and security of secure group messaging,” Institute of Science and Technology Austria, 2024.","ama":"Pascual Perez G. On the efficiency and security of secure group messaging. 2024. doi:<a href=\"https://doi.org/10.15479/at:ista:18088\">10.15479/at:ista:18088</a>","short":"G. Pascual Perez, On the Efficiency and Security of Secure Group Messaging, Institute of Science and Technology Austria, 2024.","ista":"Pascual Perez G. 2024. On the efficiency and security of secure group messaging. Institute of Science and Technology Austria."},"type":"dissertation","project":[{"_id":"2564DBCA-B435-11E9-9278-68D0E5697425","call_identifier":"H2020","name":"International IST Doctoral Program","grant_number":"665385"}],"ec_funded":1,"oa_version":"Published Version","doi":"10.15479/at:ista:18088","title":"On the efficiency and security of secure group messaging","author":[{"last_name":"Pascual Perez","first_name":"Guillermo","full_name":"Pascual Perez, Guillermo","orcid":"0000-0001-8630-415X","id":"2D7ABD02-F248-11E8-B48F-1D18A9856A87"}],"publisher":"Institute of Science and Technology Austria","date_published":"2024-09-18T00:00:00Z","file":[{"file_name":"thesis_bundle.zip","relation":"source_file","creator":"gpascual","access_level":"closed","checksum":"ce0dca715b3df48e52e2e891b6ac1bc5","file_id":"18099","file_size":11917734,"date_created":"2024-09-19T12:35:38Z","content_type":"application/x-zip-compressed","date_updated":"2024-09-19T12:35:38Z"},{"file_id":"18100","file_size":2729427,"access_level":"open_access","checksum":"4a2c72e90f1a0ef2a13cff800f8d1265","content_type":"application/pdf","date_updated":"2024-09-19T12:36:08Z","date_created":"2024-09-19T12:36:08Z","file_name":"thesis_gpasper.pdf","creator":"gpascual","relation":"main_file"}],"article_processing_charge":"No","day":"18","abstract":[{"lang":"eng","text":"Instant messaging applications like Whatsapp, Signal or Telegram have become ubiquitous in today's society.\r\nMany of them provide not only end-to-end encryption, but also security guarantees even when the key material gets compromised.\r\nThese are achieved through frequent key update performed by users.\r\nIn particular, the compromise of a group key should preserve confidentiality of previously exchanged messages (forward secrecy), and a subsequent key update will ensure security for future ones (post-compromise security).\r\nThough great protocols for one-on-one communication have been known for some time, the design of ones that scale efficiently for larger groups while achieving akin security guarantees is a hard problem.\r\nA great deal of research has been aimed at this topic, much of it under the umbrella of the Messaging Layer Security (MLS) working group at the IETF. \r\nStarted in 2018, this joint effort by academics and industry culminated in 2023 with the publication of the first standard for secure group messaging [IETF, RFC9420].\r\n\r\nAt the core of secure group messaging is a cryptographic primitive termed Continuous Group Key Agreement, or CGKA [Alwen et al. 2021], that essentially allows a changing group of users to agree on a common key with the added functionality security against compromises is achieved by users asynchronously issuing a key update. In this thesis we contribute to the understanding of CGKA across different angles.\r\nFirst, we present a new technique to effect dynamic operations in groups, i.e., add or remove members, that can be more efficient that the one employed by MLS in certain settings.\r\nConsidering the setting of users belonging to multiple overlapping groups, we then show lowerbounds on the communication cost of constructions that leverage said overlap, at the same time showing protocols that are asymptotically optimal and efficient for practical settings, respectively. Along the way, we show that the communication cost of key updates in MLS is average-cost optimal.\r\nAn important feature in CGKA protocols, particularly for big groups, is the possibility of executing several group operations concurrently. While later versions of MLS support this, they do at the cost of worsening the communication efficiency of future group operations.\r\nIn this thesis we introduce two new protocols that permit concurrency without any negative effect on efficiency. Our protocols circumvent previously existing lower bounds by satisfying a new notion of post-compromise security that only asks for security to be re-established after a certain number of key updates have taken place. While this can be slower than MLS in terms of rounds of communication, we show that it leads to more efficient overall communication. \r\nAdditionally, we introduce a new technique that allows group members to decrease the information they need to store and download, which makes one of our protocols enjoy much lower download cost than any other existing CGKA constructions. "}],"OA_place":"publisher","publication_status":"published","year":"2024","status":"public","corr_author":"1"},{"publication_status":"published","abstract":[{"text":"Payment channel networks are a promising approach to improve the scalability bottleneck\r\nof cryptocurrencies. Two design principles behind payment channel networks are\r\nefficiency and privacy. Payment channel networks improve efficiency by allowing users\r\nto transact in a peer-to-peer fashion along multi-hop routes in the network, avoiding\r\nthe lengthy process of consensus on the blockchain. Transacting over payment channel\r\nnetworks also improves privacy as these transactions are not broadcast to the blockchain.\r\nDespite the influx of recent protocols built on top of payment channel networks and\r\ntheir analysis, a common shortcoming of many of these protocols is that they typically\r\nfocus only on either improving efficiency or privacy, but not both. Another limitation\r\non the efficiency front is that the models used to model actions, costs and utilities of\r\nusers are limited or come with unrealistic assumptions.\r\nThis thesis aims to address some of the shortcomings of recent protocols and algorithms\r\non payment channel networks, particularly in their privacy and efficiency aspects. We\r\nfirst present a payment route discovery protocol based on hub labelling and private\r\ninformation retrieval that hides the route query and is also efficient. We then present\r\na rebalancing protocol that formulates the rebalancing problem as a linear program\r\nand solves the linear program using multiparty computation so as to hide the channel\r\nbalances. The rebalancing solution as output by our protocol is also globally optimal.\r\nWe go on to develop more realistic models of the action space, costs, and utilities of\r\nboth existing and new users that want to join the network. In each of these settings,\r\nwe also develop algorithms to optimise the utility of these users with good guarantees\r\non the approximation and competitive ratios.","lang":"eng"}],"OA_place":"publisher","year":"2023","status":"public","corr_author":"1","publisher":"Institute of Science and Technology Austria","author":[{"last_name":"Yeo","orcid":"0009-0001-3676-4809","id":"2D82B818-F248-11E8-B48F-1D18A9856A87","first_name":"Michelle X","full_name":"Yeo, Michelle X"}],"date_published":"2023-11-10T00:00:00Z","file":[{"creator":"cchlebak","relation":"source_file","file_name":"thesis_yeo.zip","date_updated":"2023-11-23T10:29:55Z","content_type":"application/x-zip-compressed","date_created":"2023-11-23T10:29:55Z","file_size":3037720,"file_id":"14598","checksum":"521c72818d720a52b377207b2ee87b6a","access_level":"closed"},{"file_size":2717256,"file_id":"14599","success":1,"checksum":"0ed5d16899687aecf13d843c9878c9f2","access_level":"open_access","content_type":"application/pdf","date_updated":"2023-11-23T10:30:08Z","date_created":"2023-11-23T10:30:08Z","file_name":"thesis_yeo.pdf","creator":"cchlebak","relation":"main_file"}],"article_processing_charge":"No","day":"10","oa_version":"Published Version","doi":"10.15479/14506","title":"Advances in efficiency and privacy in payment channel network analysis","project":[{"call_identifier":"H2020","name":"International IST Doctoral Program","_id":"2564DBCA-B435-11E9-9278-68D0E5697425","grant_number":"665385"}],"ec_funded":1,"date_created":"2023-11-10T08:10:43Z","date_updated":"2026-04-07T13:29:45Z","file_date_updated":"2023-11-23T10:30:08Z","citation":{"chicago":"Yeo, Michelle X. “Advances in Efficiency and Privacy in Payment Channel Network Analysis.” Institute of Science and Technology Austria, 2023. <a href=\"https://doi.org/10.15479/14506\">https://doi.org/10.15479/14506</a>.","apa":"Yeo, M. X. (2023). <i>Advances in efficiency and privacy in payment channel network analysis</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/14506\">https://doi.org/10.15479/14506</a>","mla":"Yeo, Michelle X. <i>Advances in Efficiency and Privacy in Payment Channel Network Analysis</i>. Institute of Science and Technology Austria, 2023, doi:<a href=\"https://doi.org/10.15479/14506\">10.15479/14506</a>.","ista":"Yeo MX. 2023. Advances in efficiency and privacy in payment channel network analysis. Institute of Science and Technology Austria.","ama":"Yeo MX. Advances in efficiency and privacy in payment channel network analysis. 2023. doi:<a href=\"https://doi.org/10.15479/14506\">10.15479/14506</a>","short":"M.X. Yeo, Advances in Efficiency and Privacy in Payment Channel Network Analysis, Institute of Science and Technology Austria, 2023.","ieee":"M. X. Yeo, “Advances in efficiency and privacy in payment channel network analysis,” Institute of Science and Technology Austria, 2023."},"type":"dissertation","related_material":{"record":[{"status":"deleted","id":"13238","relation":"part_of_dissertation"},{"id":"9969","relation":"part_of_dissertation","status":"public"},{"status":"public","id":"14490","relation":"part_of_dissertation"}]},"user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","oa":1,"department":[{"_id":"GradSch"},{"_id":"KrPi"}],"_id":"14506","alternative_title":["ISTA Thesis"],"has_accepted_license":"1","page":"162","degree_awarded":"PhD","publication_identifier":{"issn":["2663-337X"]},"ddc":["000"],"month":"11","language":[{"iso":"eng"}],"supervisor":[{"last_name":"Pietrzak","id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87","orcid":"0000-0002-9139-1654","full_name":"Pietrzak, Krzysztof Z","first_name":"Krzysztof Z"}]},{"date_published":"2021-09-23T00:00:00Z","publisher":"Institute of Science and Technology Austria","author":[{"last_name":"Klein","full_name":"Klein, Karen","first_name":"Karen","id":"3E83A2F8-F248-11E8-B48F-1D18A9856A87"}],"article_processing_charge":"No","day":"23","file":[{"creator":"cchlebak","relation":"main_file","file_name":"thesis_pdfa.pdf","content_type":"application/pdf","date_updated":"2021-10-04T12:22:33Z","date_created":"2021-10-04T12:22:33Z","file_id":"10082","file_size":2104726,"access_level":"open_access","success":1,"checksum":"73a44345c683e81f3e765efbf86fdcc5"},{"content_type":"application/x-zip-compressed","date_updated":"2022-03-10T12:15:18Z","date_created":"2021-10-05T07:04:37Z","file_size":9538359,"file_id":"10085","checksum":"7b80df30a0e686c3ef6a56d4e1c59e29","access_level":"closed","creator":"cchlebak","relation":"source_file","file_name":"thesis_final (1).zip"}],"year":"2021","abstract":[{"lang":"eng","text":"Many security definitions come in two flavors: a stronger “adaptive” flavor, where the adversary can arbitrarily make various choices during the course of the attack, and a weaker “selective” flavor where the adversary must commit to some or all of their choices a-priori. For example, in the context of identity-based encryption, selective security requires the adversary to decide on the identity of the attacked party at the very beginning of the game whereas adaptive security allows the attacker to first see the master public key and some secret keys before making this choice. Often, it appears to be much easier to achieve selective security than it is to achieve adaptive security. A series of several recent works shows how to cleverly achieve adaptive security in several such scenarios including generalized selective decryption [Pan07][FJP15], constrained PRFs [FKPR14], and Yao’s garbled circuits [JW16]. Although the above works expressed vague intuition that they share a common technique, the connection was never made precise. In this work we present a new framework (published at Crypto ’17 [JKK+17a]) that connects all of these works and allows us to present them in a unified and simplified fashion. Having the framework in place, we show how to achieve adaptive security for proxy re-encryption schemes (published at PKC ’19 [FKKP19]) and provide the first adaptive security proofs for continuous group key agreement protocols (published at S&P ’21 [KPW+21]). Questioning optimality of our framework, we then show that currently used proof techniques cannot lead to significantly better security guarantees for \"graph-building\" games (published at TCC ’21 [KKPW21a]). These games cover generalized selective decryption, as well as the security of prominent constructions for constrained PRFs, continuous group key agreement, and proxy re-encryption. Finally, we revisit the adaptive security of Yao’s garbled circuits and extend the analysis of Jafargholi and Wichs in two directions: While they prove adaptive security only for a modified construction with increased online complexity, we provide the first positive results for the original construction by Yao (published at TCC ’21 [KKP21a]). On the negative side, we prove that the results of Jafargholi and Wichs are essentially optimal by showing that no black-box reduction can provide a significantly better security bound (published at Crypto ’21 [KKPW21c])."}],"OA_place":"publisher","publication_status":"published","status":"public","corr_author":"1","project":[{"call_identifier":"H2020","name":"Teaching Old Crypto New Tricks","_id":"258AA5B2-B435-11E9-9278-68D0E5697425","grant_number":"682815"}],"ec_funded":1,"acknowledgement":"I want to acknowledge the funding by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (682815 - TOCNeT).\r\n","oa_version":"Published Version","doi":"10.15479/at:ista:10035","title":"On the adaptive security of graph-based games","user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","related_material":{"record":[{"relation":"part_of_dissertation","id":"10044","status":"public"},{"id":"10048","relation":"part_of_dissertation","status":"public"},{"status":"public","id":"10041","relation":"part_of_dissertation"},{"id":"10049","relation":"part_of_dissertation","status":"public"},{"id":"637","relation":"part_of_dissertation","status":"public"},{"id":"6430","relation":"part_of_dissertation","status":"public"}]},"oa":1,"date_updated":"2026-04-16T09:52:03Z","file_date_updated":"2022-03-10T12:15:18Z","date_created":"2021-09-23T07:31:44Z","citation":{"mla":"Klein, Karen. <i>On the Adaptive Security of Graph-Based Games</i>. Institute of Science and Technology Austria, 2021, doi:<a href=\"https://doi.org/10.15479/at:ista:10035\">10.15479/at:ista:10035</a>.","chicago":"Klein, Karen. “On the Adaptive Security of Graph-Based Games.” Institute of Science and Technology Austria, 2021. <a href=\"https://doi.org/10.15479/at:ista:10035\">https://doi.org/10.15479/at:ista:10035</a>.","apa":"Klein, K. (2021). <i>On the adaptive security of graph-based games</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/at:ista:10035\">https://doi.org/10.15479/at:ista:10035</a>","ieee":"K. Klein, “On the adaptive security of graph-based games,” Institute of Science and Technology Austria, 2021.","ista":"Klein K. 2021. On the adaptive security of graph-based games. Institute of Science and Technology Austria.","short":"K. Klein, On the Adaptive Security of Graph-Based Games, Institute of Science and Technology Austria, 2021.","ama":"Klein K. On the adaptive security of graph-based games. 2021. doi:<a href=\"https://doi.org/10.15479/at:ista:10035\">10.15479/at:ista:10035</a>"},"type":"dissertation","month":"09","ddc":["519"],"supervisor":[{"full_name":"Pietrzak, Krzysztof Z","first_name":"Krzysztof Z","id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87","orcid":"0000-0002-9139-1654","last_name":"Pietrzak"}],"tmp":{"image":"/images/cc_by.png","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","short":"CC BY (4.0)"},"language":[{"iso":"eng"}],"license":"https://creativecommons.org/licenses/by/4.0/","alternative_title":["ISTA Thesis"],"page":"276","has_accepted_license":"1","_id":"10035","department":[{"_id":"GradSch"},{"_id":"KrPi"}],"publication_identifier":{"issn":["2663-337X"]},"degree_awarded":"PhD"},{"status":"public","corr_author":"1","year":"2020","abstract":[{"lang":"eng","text":"A search problem lies in the complexity class FNP if a solution to the given instance of the problem can be verified efficiently. The complexity class TFNP consists of all search problems in FNP that are total in the sense that a solution is guaranteed to exist. TFNP contains a host of interesting problems from fields such as algorithmic game theory, computational topology, number theory and combinatorics. Since TFNP is a semantic class, it is unlikely to have a complete problem. Instead, one studies its syntactic subclasses which are defined based on the combinatorial principle used to argue totality. Of particular interest is the subclass PPAD, which contains important problems\r\nlike computing Nash equilibrium for bimatrix games and computational counterparts of several fixed-point theorems as complete. In the thesis, we undertake the study of averagecase hardness of TFNP, and in particular its subclass PPAD.\r\nAlmost nothing was known about average-case hardness of PPAD before a series of recent results showed how to achieve it using a cryptographic primitive called program obfuscation.\r\nHowever, it is currently not known how to construct program obfuscation from standard cryptographic assumptions. Therefore, it is desirable to relax the assumption under which average-case hardness of PPAD can be shown. In the thesis we take a step in this direction. First, we show that assuming the (average-case) hardness of a numbertheoretic\r\nproblem related to factoring of integers, which we call Iterated-Squaring, PPAD is hard-on-average in the random-oracle model. Then we strengthen this result to show that the average-case hardness of PPAD reduces to the (adaptive) soundness of the Fiat-Shamir Transform, a well-known technique used to compile a public-coin interactive protocol into a non-interactive one. As a corollary, we obtain average-case hardness for PPAD in the random-oracle model assuming the worst-case hardness of #SAT. Moreover, the above results can all be strengthened to obtain average-case hardness for the class CLS ⊆ PPAD.\r\nOur main technical contribution is constructing incrementally-verifiable procedures for computing Iterated-Squaring and #SAT. By incrementally-verifiable, we mean that every intermediate state of the computation includes a proof of its correctness, and the proof can be updated and verified in polynomial time. Previous constructions of such procedures relied on strong, non-standard assumptions. Instead, we introduce a technique called recursive proof-merging to obtain the same from weaker assumptions. "}],"OA_place":"publisher","publication_status":"published","article_processing_charge":"No","day":"25","file":[{"checksum":"b39e2e1c376f5819b823fb7077491c64","access_level":"open_access","file_size":1622742,"file_id":"7897","date_created":"2020-05-26T14:08:13Z","date_updated":"2020-07-14T12:48:04Z","content_type":"application/pdf","file_name":"2020_Thesis_Kamath.pdf","relation":"main_file","creator":"dernst"},{"date_updated":"2020-07-14T12:48:04Z","content_type":"application/x-zip-compressed","date_created":"2020-05-26T14:08:23Z","file_id":"7898","file_size":15301529,"access_level":"closed","checksum":"8b26ba729c1a85ac6bea775f5d73cdc7","creator":"dernst","relation":"source_file","file_name":"Thesis_Kamath.zip"}],"date_published":"2020-05-25T00:00:00Z","publisher":"Institute of Science and Technology Austria","author":[{"first_name":"Chethan","full_name":"Kamath Hosdurg, Chethan","orcid":"0009-0006-6812-7317","id":"4BD3F30E-F248-11E8-B48F-1D18A9856A87","last_name":"Kamath Hosdurg"}],"doi":"10.15479/AT:ISTA:7896","title":"On the average-case hardness of total search problems","oa_version":"Published Version","ec_funded":1,"project":[{"grant_number":"259668","_id":"258C570E-B435-11E9-9278-68D0E5697425","call_identifier":"FP7","name":"Provable Security for Physical Cryptography"},{"grant_number":"682815","call_identifier":"H2020","name":"Teaching Old Crypto New Tricks","_id":"258AA5B2-B435-11E9-9278-68D0E5697425"}],"citation":{"mla":"Kamath Hosdurg, Chethan. <i>On the Average-Case Hardness of Total Search Problems</i>. Institute of Science and Technology Austria, 2020, doi:<a href=\"https://doi.org/10.15479/AT:ISTA:7896\">10.15479/AT:ISTA:7896</a>.","apa":"Kamath Hosdurg, C. (2020). <i>On the average-case hardness of total search problems</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/AT:ISTA:7896\">https://doi.org/10.15479/AT:ISTA:7896</a>","chicago":"Kamath Hosdurg, Chethan. “On the Average-Case Hardness of Total Search Problems.” Institute of Science and Technology Austria, 2020. <a href=\"https://doi.org/10.15479/AT:ISTA:7896\">https://doi.org/10.15479/AT:ISTA:7896</a>.","ieee":"C. Kamath Hosdurg, “On the average-case hardness of total search problems,” Institute of Science and Technology Austria, 2020.","ama":"Kamath Hosdurg C. On the average-case hardness of total search problems. 2020. doi:<a href=\"https://doi.org/10.15479/AT:ISTA:7896\">10.15479/AT:ISTA:7896</a>","short":"C. Kamath Hosdurg, On the Average-Case Hardness of Total Search Problems, Institute of Science and Technology Austria, 2020.","ista":"Kamath Hosdurg C. 2020. On the average-case hardness of total search problems. Institute of Science and Technology Austria."},"type":"dissertation","date_updated":"2026-04-08T07:24:42Z","file_date_updated":"2020-07-14T12:48:04Z","date_created":"2020-05-26T14:08:55Z","oa":1,"user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","related_material":{"record":[{"status":"public","id":"6677","relation":"part_of_dissertation"}]},"publication_identifier":{"issn":["2663-337X"]},"degree_awarded":"PhD","alternative_title":["ISTA Thesis"],"has_accepted_license":"1","page":"126","_id":"7896","department":[{"_id":"KrPi"}],"tmp":{"image":"/images/cc_by.png","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","short":"CC BY (4.0)"},"supervisor":[{"last_name":"Pietrzak","orcid":"0000-0002-9139-1654","id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87","first_name":"Krzysztof Z","full_name":"Pietrzak, Krzysztof Z"}],"language":[{"iso":"eng"}],"month":"05","ddc":["000"]},{"article_processing_charge":"No","day":"05","file":[{"relation":"main_file","creator":"dernst","file_name":"2018_Thesis_Abusalah.pdf","date_created":"2019-04-09T06:43:41Z","content_type":"application/pdf","date_updated":"2020-07-14T12:48:11Z","access_level":"open_access","checksum":"c4b5f7d111755d1396787f41886fc674","file_id":"6245","file_size":876241},{"date_created":"2019-04-09T06:43:41Z","date_updated":"2020-07-14T12:48:11Z","content_type":"application/x-gzip","checksum":"0f382ac56b471c48fd907d63eb87dafe","access_level":"closed","file_size":2029190,"file_id":"6246","relation":"source_file","creator":"dernst","file_name":"2018_Thesis_Abusalah_source.tar.gz"}],"date_published":"2018-09-05T00:00:00Z","publisher":"Institute of Science and Technology Austria","author":[{"full_name":"Abusalah, Hamza M","first_name":"Hamza M","id":"40297222-F248-11E8-B48F-1D18A9856A87","last_name":"Abusalah"}],"pubrep_id":"1046","status":"public","corr_author":"1","year":"2018","abstract":[{"text":"A proof system is a protocol between a prover and a verifier over a common input in which an honest prover convinces the verifier of the validity of true statements. Motivated by the success of decentralized cryptocurrencies, exemplified by Bitcoin, the focus of this thesis will be on proof systems which found applications in some sustainable alternatives to Bitcoin, such as the Spacemint and Chia cryptocurrencies. In particular, we focus on proofs of space and proofs of sequential work.\r\nProofs of space (PoSpace) were suggested as more ecological, economical, and egalitarian alternative to the energy-wasteful proof-of-work mining of Bitcoin. However, the state-of-the-art constructions of PoSpace are based on sophisticated graph pebbling lower bounds, and are therefore complex. Moreover, when these PoSpace are used in cryptocurrencies like Spacemint, miners can only start mining after ensuring that a commitment to their space is already added in a special transaction to the blockchain. Proofs of sequential work (PoSW) are proof systems in which a prover, upon receiving a statement x and a time parameter T, computes a proof which convinces the verifier that T time units had passed since x was received. Whereas Spacemint assumes synchrony to retain some interesting Bitcoin dynamics, Chia requires PoSW with unique proofs, i.e., PoSW in which it is hard to come up with more than one accepting proof for any true statement. In this thesis we construct simple and practically-efficient PoSpace and PoSW. When using our PoSpace in cryptocurrencies, miners can start mining on the fly, like in Bitcoin, and unlike current constructions of PoSW, which either achieve efficient verification of sequential work, or faster-than-recomputing verification of correctness of proofs, but not both at the same time, ours achieve the best of these two worlds.","lang":"eng"}],"publication_status":"published","OA_place":"publisher","ec_funded":1,"project":[{"_id":"258C570E-B435-11E9-9278-68D0E5697425","name":"Provable Security for Physical Cryptography","call_identifier":"FP7","grant_number":"259668"},{"_id":"258AA5B2-B435-11E9-9278-68D0E5697425","name":"Teaching Old Crypto New Tricks","call_identifier":"H2020","grant_number":"682815"}],"title":"Proof systems for sustainable decentralized cryptocurrencies","doi":"10.15479/AT:ISTA:TH_1046","oa_version":"Published Version","publist_id":"7971","oa":1,"user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","related_material":{"record":[{"status":"public","relation":"part_of_dissertation","id":"559"},{"id":"1236","relation":"part_of_dissertation","status":"public"},{"status":"public","id":"1235","relation":"part_of_dissertation"},{"status":"public","id":"1229","relation":"part_of_dissertation"}]},"citation":{"mla":"Abusalah, Hamza M. <i>Proof Systems for Sustainable Decentralized Cryptocurrencies</i>. Institute of Science and Technology Austria, 2018, doi:<a href=\"https://doi.org/10.15479/AT:ISTA:TH_1046\">10.15479/AT:ISTA:TH_1046</a>.","apa":"Abusalah, H. M. (2018). <i>Proof systems for sustainable decentralized cryptocurrencies</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/AT:ISTA:TH_1046\">https://doi.org/10.15479/AT:ISTA:TH_1046</a>","chicago":"Abusalah, Hamza M. “Proof Systems for Sustainable Decentralized Cryptocurrencies.” Institute of Science and Technology Austria, 2018. <a href=\"https://doi.org/10.15479/AT:ISTA:TH_1046\">https://doi.org/10.15479/AT:ISTA:TH_1046</a>.","ieee":"H. M. Abusalah, “Proof systems for sustainable decentralized cryptocurrencies,” Institute of Science and Technology Austria, 2018.","short":"H.M. Abusalah, Proof Systems for Sustainable Decentralized Cryptocurrencies, Institute of Science and Technology Austria, 2018.","ama":"Abusalah HM. Proof systems for sustainable decentralized cryptocurrencies. 2018. doi:<a href=\"https://doi.org/10.15479/AT:ISTA:TH_1046\">10.15479/AT:ISTA:TH_1046</a>","ista":"Abusalah HM. 2018. Proof systems for sustainable decentralized cryptocurrencies. Institute of Science and Technology Austria."},"type":"dissertation","date_updated":"2026-04-08T14:10:22Z","file_date_updated":"2020-07-14T12:48:11Z","date_created":"2018-12-11T11:44:32Z","supervisor":[{"orcid":"0000-0002-9139-1654","id":"3E04A7AA-F248-11E8-B48F-1D18A9856A87","first_name":"Krzysztof Z","full_name":"Pietrzak, Krzysztof Z","last_name":"Pietrzak"}],"language":[{"iso":"eng"}],"month":"09","ddc":["004"],"publication_identifier":{"issn":["2663-337X"]},"degree_awarded":"PhD","alternative_title":["ISTA Thesis"],"page":"59","has_accepted_license":"1","_id":"83","department":[{"_id":"KrPi"}]}]