Lenstra proposed a method by which information can be efficiently in a public key N in RSA encryption. Since then, many methods such as the additional key escrow function and a visible public key have been proposed. Lenstra made an assertion that the size of embeddable information is up to half the length of a public key, but he did not mention the strict upper bound of the size. In this paper, we analytially examine the Lenstra algorithm both in theory and implementation, and calcuate the upper bound of the size of information that can be efficiently embedded in an RSA public key.
['Motoki Kitahara', 'Takanori Yasuda', 'Takashi Nishide', 'Kouichi Sakurai']
Upper bound of the length of information embedd in RSA public key efficiently