Patent ID: 7590854

Claim:
A computer-implemented method of generating a digital signature on a message M for a signer E t which is an entity t levels below an entity E 0 in a hierarchical system including at least the entities E 0 , E 1 , . . . , E t , t≧2, wherein each entity E i (i=1, . . . ,t) is a child of entity E i−1 in the hierarchical system, the method comprising: (1) obtaining the signer's secret key S t which is a member of a group G 1 ; (2) obtaining the signer's integer secret s t ; (3) generating a signature component Sig on the message M as a value Sig=S t +s t P M wherein: “+” is a group operation in the group G 1 ; and P M is a value depending on the message M and is a member of the group G 1 .