On the security of some proxy blind signature schemes

A proxy blind signature scheme is a digital signature scheme which combines the properties of proxy signature and blind signature schemes. Recently, Tan et al. proposed two proxy blind signature schemes based on DLP and ECDLP respectively. Later, compared with Tan et al.'s scheme, Lal and Awasthi further proposed a more efficient proxy blind signature scheme. In this paper, we show that both Tan et al.'s schemes do not satisfy the unforgeability and unlinkability properties. Moreover, we also point out that Lal and Awasthi's scheme does not possess the unlinkability property either. (C) 2004 Elsevier Inc. All rights reserved.