Abstract: In the standard model an UCMA security IBS scheme was proposed by Peterson and Schuldt, which was based on computational Diffie-Hellman problem in bilinear pairing group. Two independent Waters' identity hash functions were directly employed to treat the user's identity and the signature message, respectively, so PS's IBS scheme had a great number of public keys. An improved parameters selecting method was proposed in the new scheme, which only needs a small number of public keys,and the new scheme can be proved security in the standard model.

Key words: Identity-based signature, Standard model, Short public key