International Association
for Cryptologic Research

The Open Smart Grid Protocol (OSGP) is a widely used industry standard for exchanging sensitive data between devices inside of smart grids. For message confidentiality, OSGP implements a customised form of the RC4 stream cipher. In this work, we show how already known weaknesses of RC4 can be exploited to successfully attack the OSGP implementation as well. The attack modification is able to effectively derive the secret OSGP encryption and decryption key, given that an attacker can accumulate the cipher streams of approximately 90,000 messages. The possession of this key allows the attacker to decrypt all data intercepted on the OSGP smart grid and thereby obtain privacy critical information of its participants.