Patent ID: 8028163

Claim:
A method of providing a digital signature to a data entry for storing in a data repository, the data entry comprising a root and a tree of data elements at different levels from the root, the method comprising: identifying, by a processor, data elements of the data entry which are to be digitally signed; performing, by the processor, a function on those identified data elements in a level furthest from the root to obtain a first set of results relating to that level; performing, by the processor, the function on the first set of results to obtain a level function value derived from the identified data elements in the level; changing, by the processor, level to a new level one nearer to the root, and performing the function on a second set of results comprising those identified data elements in the new level as well as the level function value for the level one further from the root, thereby to obtain a level function value derived from the identified data elements in the new level, wherein the changing of level is repeated until the level is the first level after the root, and a single function value is obtained which combines function values for all of the identified data elements.