Personal information, especially certified personal information, can be very valuable to its subject, but it can also be abused by other parties for identify theft, blackmail, fraud, and more. One partial solution to the problem is credentials, whereby personal information is tied to identity, for example by a photo or signature on a physical credential. We present an efficient scheme for large, redactable, digital credentials that allow certified personal attributes to safely be used to provide identification. A novel method is provided for combining credentials, even when they were originally issued by different authorities. Compared to other redactable digital credential schemes, the proposed scheme is approximately two orders of magnitude faster, due to aiming for auditability over anonymity. In order to expand this scheme to hold other records, medical records for example, we present a method for efficient signatures on redactable data where there are dependencies between different pieces of data. Positive results are shown using both artificial datasets and a dataset derived from a Linux package manager. Electronic credentials must of course be held in a physical device with electronic memory. To hedge against the loss or compromise of the physical device holding a user's credentials, the credentials may be split up. An architecture is developed and prototyped for using split-up credentials, with part of the credentials held by a network attached agent. This architecture is generalized into a framework for running identity agents with various capabilities. Finally, a system for securely sharing medical records is built upon the generalized agent framework. The medical records are optionally stored using the redactable digital credentials, for source verifiability.

The objective of the proposed research is to answer the question of how to provide verification and redactability to medical documents at a manageable computation cost to all parties involved. The approach for this solution examines the use of Merkle Hash Trees to provide the redaction and verification characteristics required. Using the Merkle Hash Tree, various Continuity of Care Documents will have their various elements extracted for storage in the signature scheme. An analysis of the approach and the various characteristics that made this approach a likely candidate for success are provided within. A description of a framework implementation and a sample application are provided to demonstrate potential uses of the system. Finally, results seen from various experiments with the framework are included to provide concrete evidence of a solution to the question which was the focus of this research.

For this work, two algorithms have been developed to improve the performance of the inconsistency detection by using Merkle trees. The first builds a hash tree from a database schema version, and the second compares two hash trees to find where changes have occurred. The results of performance testing done on the hash tree approach compared to the current approach used by Cisco where all data in the schema is traversed, shows that the hash tree algorithm for inconsistency detection performs significantly better than the complete traversal algorithm in all cases tested, with the exception of when all nodes have changed in the tree. The factor of improvement is directly related to the number of nodes that have to be traversed for the hash tree, which in turn depends on the number of changes done between versions and the positioning in the schema of the nodes that have changed. The real-life example scenarios used for performance testing show that on average, the hash tree algorithm only needs to traverse 1,5% of the number of nodes that the complete traversal algorithm used by Cisco does, and on average gives a 200 times improvement in performance. Even in the worst real-life case used for testing, the hash tree algorithm performed five times better than the complete traversal algorithm. / I detta arbete har två algoritmer utvecklats for att förbättra prestandan på processen att hitta skillnader mellan schemana genom att använda Merkle träd. Den första bygger ett hashträd från schemaversionen, och den andra jämför två hashträd för att hitta var förändringar har skett. Resultaten från prestandautvärderingen som gjorts på hashträdalgoritmen jämfört med nuvarande algoritm som används på Cisco där all data i schemat traverseras, visar att hashträdalgoritmen presterar signifikant bättre än algoritmen som traverserar all data i alla fall som testats, förutom då alla noder har ändrats i trädet. Förbättringsfaktorn är direkt kopplad till antalet noder som behöver traverseras för hashträdalgoritmen, vilket i sin tur beror på antalet förändringar som skett mellan versionerna och positioneringen i schemat av de noder som har förändrats. De exempelscenarior som har tagits från riktiga uppdateringar som har skett för existerande scheman visar att i genomsnitt behöver hashträdalgoritmen bara traversera 1,5% av noderna som den nuvarande algoritmen som används av Cisco måste traversera, och hashträdalgoritmen ger i genomsnitt en 200 gånger prestandaförbättring. Även i det värsta fallet för dessa uppdateringar tagna från verkliga scenarier presterade hashträdalgoritmen fem gånger bättre än algoritmen som traverserar all data i schemat.

This master's thesis explains basics of the longest prefix match (LPM) problem. It analyzes and describes chosen LPM algorithms considering their speed, memory requirements and an ability to implement them in hardware. On the basis of former findings it proposes a new algorithm Generic Hash Tree Bitmap. It is much faster than many other approaches, while its memory requirements are even lower. An implementation of the proposed algorithm has become a part of the Netbench library.