Blind group/ring signatures are useful for applications such as e-cash and e-voting systems. In this paper, we show that the blindness of some existing blind group/ring signature schemes is easy to break by a malicious anonymous signer of dynamic groups. However, this risk has not been pointed out in these proposals, which may cause misuse of the schemes. Fortunately, for static groups, it is possible to integrate the blindness of message into group/ring signatures. An efficient static blind ring signature is proposed with its security provable under the extended ROS assumptions in the random oracle model plus the generic group model. After the group public key is generated, the space, time, and communication complexities of the relevant parameters and operations are constant. © Springer-Verlag Berlin Heidelberg 2006.