Maryam Rajabzadeh Asaar - EE Department, Sharif University of Technology, Tehran, Iran
Mahmoud Salmasizadeh - Electronics Research Center, Sharif University of Technology, Tehran, Iran
Alireza Sharifi - EE Department, Sharif University of Technology, Tehran, Iran

Two of the most important security requirements of a blind proxy signature scheme are unlinkability which states that it should be impossible to establish a link between the identity of a proxy signer and his/her signature-message pair and unforgeability which states that it should be impossible to create a valid proxy signature instead of proxy signer. In this paper, we show that some blind proxy signature schemes that were proposed without the Trusted Third Party don't satisfy the unlinkabiliy or uforgeabililty property. In some of them, the original signer can track who receives proxy capability and in others, a dishonest original signer can forge the proxy key and generate a valid blind proxy signature using a forgery attack instead of the proxy signer.

proxy signature, blind proxy signature, security analysis, unforgeability, unlinkability