Abstract

A method of generating digital signatures for signing an infinitely expandable series of messages Mi. An infinitely expandable tree of signature nodes is used, where each node can be used to sign a message. Each node is also used to sign up to k subnodes, where k is an integer greater than one. Each signature used, both for signing messages and for signing subnodes, is a one time signature, which in the preferred embodiment is based on a one-way function F. The function F is made public. To sign a message Mi the signer selects a previously unused node (i.e., node i) from the signature tree. The message signing key at this node is then used to sign this message. The sequence of nodes from the root of the tree (i.e. node l) to node i is then used to verify that the message signature is correct and has not been tampered with. Furthermore, this process proves that the message has not been tampered with. Advantages of the invention include the infinite expandability of the signature tree, dependable verification of messages based on the use of secure one time signatures (e.g., which may be based on one way functions), the small amount of computation required to set up a signature tree, the small amount of storage required to maintain a tree, and the ability to implement the invention using high speed conventional encryption equipment and methods.

Other References

• Merkle, Secrecy, Authentication, and Public Key Systems; UMI Research Press, Ann Arbor, Chaps. 5-6 (1979)
• Diffie et al., "New Directions in Cryptography", "IEEE Trans. on Info. Theory", vol. IT-22, No. 6, pp. 644-654 (Nov. 1976