Short signatures in the random oracle model
Louis Granboulan
Short signatures in the random oracle model Louis Granboulan? Ecole Normale Superieure Abstract. We study how digital signature schemes can generate signa- tures as short as possible, in particular in the case where partial message recovery is allowed. We give a concrete proposition named OPSSR that achieves the lower bound for message expansion, and give an exact se- curity proof of the scheme in the ideal cipher model. We extend it to the multi-key setting. We also show that this padding can be used for an asymmetric encryption scheme with minimal message expansion. Keywords: digital signature, padding, random oracle and ideal cipher models, proven security. 1 Introduction 1.1 Overview of the results A digital signature scheme allows a signer to transform an arbitrary mes- sage into a signed message, such that anyone can check the validity of the signed message using the signer's public key, but only the signer is able to generate signed messages. A signed message contains the information about the message, plus some information to prove its validity. For exam- ple in the case of a scheme without message recovery, the signed message is the concatenation of the message and of a signature. The message expansion of a signature scheme is the difference between the length of the signed message and the original message. It is the length of the signature, if there is no message recovery.
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